How much water can a tree absorb

How do trees use water?

Got Nature? Blog

Posted on September 2nd, 2021 in Forestry, Plants, Uncategorized, Wildlife, Woodlands | No Comments »

Purdue Landscape Report: Water covers approximately 71% of Earth’s surface, yet only 3% of the 326 million cubic miles of water on the planet is suitable for growing crops, such as trees. It can be said that water is the single most limiting ecological factor in tree growth and survival. It is a vital “nutrient” that must be available in adequate supply or plants decline and eventually die.

How trees use water is essential to determine water needs.

Trees use or lose water by two separate processes. First, water is taken up by tree roots from the soil and evaporated through the pores or stomata on the surface of leaves. Transpiration is a physiological process responding to soil and atmospheric factors. It is a passive movement of water through the tree system which allows columns of water to move great heights. Water movement through a tree is controlled by the tug-of-war between water availability and water movement in soil versus water loss from leaves. For example, water movement in a ring porous tree like a red oak is 92 ft/hr, in a diffuse porous tree like a basswood is 11 ft/hr, and for a pine tree is 6 ft/hr. Trees can absorb between 10 and 150 gallons of water daily, yet of all the water absorbed by plants, less than 5% remains in the plant for growth. They rely on available water in the soil to “rehydrate” during the nighttime hours, replacing the water loss during the daytime hours.

The second process is the interception of water by the surfaces of leaves, branches and trunks during rainfall, and its following evaporation. Together, these two processes are often referred to as evapotranspiration. Both transpiration and evaporation are strongly affected by the amount of sunlight, the temperature and humidity of the air, as well as wind speed as trees turn water into mist when it releases nearly 95% of the water it absorbs.

Leaves intercept water to help with stormwater management and cooling.

Just why does a tree need water? Well, nearly every plant process such as photosynthesis, respiration and transpiration rely on water to function properly. Water is an essential element as important if not more than other nutrients because it is required to put all our other elements into a form usable by the plant. Almost all essential elements are ionic forms dissolved in water, giving them the ability to move to stems, branches, and leaves for energy.

The goal of proper tree management is to prevent or reduce the impacts of water loss. If adequate soil moisture is available, water loss will go unnoticed as it is replaced naturally. Typically, we experience prolonged dry periods without rain, resulting in drought. Drought conditions are the result of long periods of time without natural rainfall. During dry conditions, soil moisture content is reduced to the point where tree roots can no longer pull the water molecules from the soil. This results in responses from the plant such as wilting, early fall color, scorching and other symptoms. Anytime there is a week without significant rainfall of at least one inch, most likely trees will need some assistance from us to supply the much-needed water for a healthy tree.

Water Your Trees, Purdue Extension-Forestry and Natural Resources (FNR) Got Nature? blog
Summer Tree Care, Purdue Landscape Report
Drought? Don’t Forget the Trees!, The Education Store, Purdue Extension resource center
Extreme Heat, Purdue Extension – IN-PREPared
Drought Information​, Indiana Department of Natural Resources
Planting Your Tree Part 1: Choosing Your Tree, Purdue Extension-FNR YouTube Channel
Tree Selection for the “Un-natural” Environment, The Education Store
Tree Pruning Essentials Video, Purdue Extension YouTube Channel
Tree Defect Identification, The Education Store
Surface Root Syndrome, The Education Store

Lindsey Purcell, Urban Forestry Specialist
Purdue Extension- Forestry and Natural Resources

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How Much Should You Water Your Tree?

Written by L. Peter MacDonagh | Posted in Design, Stormwater Management, Urban Trees

Healthy trees can grow anywhere, including cities, provided they receive enough water, soil, and sunlight. Research shows that vigorous urban trees keep people healthier, cool cities in summer, warm homes in winter, help kids learn better, decrease car accident rates, raise real estate values, and decrease crime dramatically. Even with these myriad benefits, recent heat and droughts in many parts of North America (and elsewhere) raise an uncomfortable but necessary question: how do you maintain a healthy tree when there is a shortage of water?

San Antonio, TX is an interesting place to look for an answer to this question, because the San Antonio Water System (SAWS) has higher current water needs than what’s available in its system. As a result, they have had to start purchasing water outside of their regional watershed, well-shed, and river-shed – and this has driven then to develop an efficient watering system that enables them to give trees what they need while minimizing the economic and environmental burden of purchasing water.

Mark Peterson, formerly of the Texas Forest Service and now with the San Antonio Water Department, was tasked with creating watering guidelines that would provide enough water for young trees to survive and grow, but not use any more water than absolutely necessary. Mark’s approach is what I’ll be sharing here.

Simple, But Not Easy

No matter how drought tolerant, native, or local a tree species is, almost all young to trees (typically 1 to 3 years old, or up to 5 years in Type I, Type II and especially arid regions) in man-made landscapes must be watered by people during the summer to survive and become established.  The complete extent of young tree roots in the first few years after planting is limited to the soil volume that the tree was last grown in (for example, a pot or container). Mature, established trees generally require less consistent care, but during droughts every tree must be monitored and watered adjusted accordingly.

If you are caring for young, recently planted trees, here are some good rules of thumb to follow (your mileage may vary depending on climate and tree species). Here is Mark’s watering regimen for newly planted trees.

Watering as a Science

Year Amount Frequency
First month of planting Trunks smaller than 2” (5 cm):  1 gallon per inch of trunk diameter.

Trunks larger than 2” (5cm): 2 gallons per inch of trunk diameter.

Water three (3) times a week over the root ball.


Second month of planting Trunks smaller than 2” (5 cm):  1 gallon per inch of trunk diameter.

Trunks larger than 2” (5cm): 2 gallons per inch of trunk diameter.

Water two (2) times a week over the root ball.
Third month of planting Trunks smaller than 2” (5 cm):  1 gallon per inch of trunk diameter.

Trunks larger than 2” (5cm): 2 gallons per inch of trunk diameter.

Water once (1) per week over the root ball.


Fourth to ninth month of planting Trunks smaller than 2” (5 cm):  1 gallon per inch of trunk diameter.

Trunks larger than 2” (5cm): 2 gallons per inch of trunk diameter.

Water twice per month over the root ball.


Hottest months Trunks smaller than 2” (5 cm):  1 gallon per inch of trunk diameter.

Trunks larger than 2” (5cm): 2 gallons per inch of trunk diameter.

Water twice per month over the root ball only. During a drought, water once weekly.
Cooler months Monitor and respond
Hottest months Trunks smaller than 2” (5 cm):  1 gallon per inch of trunk diameter.

Trunks larger than 2” (5cm): 2 gallons per inch of trunk diameter.

Water twice per month, twice the width of the root ball. During a drought, water once weekly.
Cooler months Monitor and respond
Hottest months Trunks smaller than 2” (5 cm):  1 gallon per inch of trunk diameter.

Trunks larger than 2” (5cm): 2 gallons per inch of trunk diameter.

Water twice per month, twice the width of the root ball. During a drought, water once weekly.
Cooler months Monitor and respond
Hottest months Trunks smaller than 2” (5 cm):  1 gallon per inch of trunk diameter.

Trunks larger than 2” (5cm): 2 gallons per inch of trunk diameter.

Water twice per month, twice the width of the root ball. During a drought, water once weekly.
Cooler months Monitor and respond


For young trees, water the roots around the trunk (not the trunk itself, and not the area outside the root ball). I also recommend creating and maintaining a 3-foot wide, 1” to 3” (2.5 cm to 7.5 cm) deep organic (wood chip) mulch ring around the trunk for its entire life, to help maintain soil moisture.

For mature trees (>25 years), or those with a trunk more than 12″ (30 cm) in diameter, water deep and occasionally. About 10 gallons per 1 inch (2.5 cm) of trunk diameter per week (ex., a tree with 12″ DBH would receive 120 gallons) during drought. If there is unlimited water, there are records of trees absorbing 150 gallons of water in a single day.

Watering as an Art

In addition to the (human-driven) watering recommendations described above, there are environmental and design decisions that can set trees in the built environment on a more secure course for getting their irrigation needs met.

Select tree species that, over the long term in typical summer weather (not droughts), won’t require supplemental watering.

The urban landscape is full of small humps, bumps, and pimples that don’t serve to gather and contain water runoff. By thoughtfully altering these forms via slopes, pipes, and berms, we can turn the entire pervious landscape into a tool for draining water to tree planting areas.  This would be a paradigm change for watering trees and managing stormwater worth billions of dollars, and billions of gallons of water, nationwide.

All trees need water during droughts. DeepRoot published some thoughts about this last summer that are worth re-reading. Trees that have access to larger volumes of loamy soil will be able to withstand dry periods better because of the water reserves the soil can contain (remember that sandy soils will drain quickly and require more frequent irrigation).  Evergreens need heavy watering going into the winter, and need watering during winter droughts.

Sometimes annuals or bulbs can look nice planted under a tree. But the tree is paying a price in root damage (caused by planting and removing flowers) and water competition for that temporary beauty. After tree establishment, I do not plant anything under trees within 10 feet of the trunk.

Watering Tools

There are a great number of available tools for watering trees depending on your needs, budget, and other site considerations.

  • Slow release watering bags (e.g. Gator Bags).
  • Rain leaders, or scuppers, can be directed towards tree trunks or below ground into the tree soil mass.
  • Flexible downspout extender can be directed towards tree trunks.
  • Clean 5 gallon bucket. Fill with hose and time speed of fill – this will tell you how many gallons per minute are being applied. A typical municipal fill = 5 gallons un 2-5 minutes
  • Rain barrels with flexible hoses attached.

  • Automatic irrigation can be great for watering hard-to-get-to trees and can be set to run occasionally for long periods of time using drip, bubbler or soaker hose.
  • Harvest cisterns – sump pump.

It’s important, particularly with mature, established trees, to water the entirety of the soil volume, even the part under paving. If there is no automatic tree watering system (bubblers, drip), I suggest using a soil watering needle with a watering hose connected.


Effective tree watering always takes place relatively slowly. (For this reason, pop-up rotary sprinkler head systems for lawns, that only turn on for a few minutes a few to several  times a week, are not the best type of watering for trees). If you use automatic irrigation to water your trees, set them to run for much longer periods of time using drip, bubbler, or soaker hose.

Still not sure?

The above are just guidelines; you should use your own experience, common sense, and (if appropriate) input from a professional when applying these to your site. Some simple questions can help you assess how much and how frequently to water your trees. Think about the following as a place to get started:

  • Are the trees young and newly planted, or mature and established?
  • How much precipitation does the area receive? How intense and frequent are the storms?
  • How warm is the average daily|high temperature in the hot season?
  • How much soil are the trees planted in?
  • What type of soil are the trees planted in?
  • Are the trees growing in a street, median, parking lot, lawn?
  • What moisture conditions does the tree prefer?
  • How does water get into the tree opening?

If you’re wondering what trees do with all that water, on hot or windy days in the summer, a whopping 95 percent of the water that the tree consumes, when available, is turned into mist by the leaves (a process called evapotranspiration). The remaining 5 percent is used to photosynthesize to manufacture sugars for food.


Thanks to Mark Peterson at San Antonio Water System, Dr.  Edward (Ed) Gilman at the University of Florida, Dr. Gary Watson with the Morton Arboretum, Jim Urban with Urban Trees + Soils, and Colorado State University Extension.

L. Peter MacDonagh is the director of science + design at the Kestrel Design Group.

Henk Sijgers / CC BY-NC 2.0

How much water a tree consumes per day. Transpiration of plants and trees.: uvova — LiveJournal

How much water a tree consumes per day. Transpiration of plants and trees.: uvova — LiveJournal ?
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year and during which there were human casualties, the automobile infrastructure was partially destroyed, and on TV they showed terrible pictures of houses floating down the river, I thought about the real reasons for such a serious increase in the water level.

Official versions of such large-scale floods: snowmelt, heavy rains and large-scale logging of the taiga to sell timber to China:

"Russian President Vladimir Putin agreed with the opinion of one of the residents of the Irkutsk region, who said that the flood would not be so large-scale, if not for massive illegal logging."

El-Murid soon wrote about the real cause of the flood in Tulun:

"The catastrophe with the rise of water by 14 meters is not explained by some kind of rain or snowmelt, as the official version says. The explanation is more prosaic: Irkutsk HPP released water, raising the water level in the Bratsk reservoir from the normative 392 meters to 402 meters - the maximum mark possible.The task was to generate additional electricity for BrAZ, which is part of Rusal.The result was the impossibility of discharging water after not very heavy rains - downstream from Bratskoye reservoir Ust-Ilimsk with 80 thousand inhabitants and dozens of other villages. Therefore, at this stage, Tulun was sacrificed, in which there are half as many people."

The answer to the question was found, but another one arose: how much can deforestation affect the increase (release) of water? After all, trees consume a considerable amount of moisture, pumping out up to 200 liters daily (especially in spring). In addition:

"The shrinking area of ​​forests is not able to carry out snow retention on the same scale, as a result of which snowmelt occurs over a vast area with much greater dynamics, this leads to more dynamic and sharp rises in rivers, which the existing irrigation facilities cannot cope with , calculated for a different flood regime. Endless cuttings contribute to the drainage of swamps - the basis of the taiga, which leads to the appearance of dry wood massifs, which burn on an unprecedented scale."

It can be added that in the forest lowlands, when trees disappear, moss dies, a square meter of which can hold up to 4 liters of water on average.

For example, in our Brotherville, too, every year the number of trees slowly but surely decreases, and the water level in the lake rises, gradually flooding the edge of the forest. But our situation is the opposite - because. the reason for this was the beavers, who made a real mess: heaped trees and built dams, blocking their paths to the ditches for the outflow of excess water.

But my site itself is also in a lowland, and with the onset of serious heavy rains or during the spring melting of snow, the ground on it turns into a sponge and puddles appear in some places. But I noticed that the lowest part of the site, where spruces and willows grow, is much drier than the upper one - where there are no trees at all. And this is even despite the presence of drainage, through which a significant part of the water goes into the forest. This begs the question: how much moisture can trees absorb? And can they drain the area? I went online to find out.

For some reason, there was very little information, but we managed to find something. For example, I discovered such a thing as transpiration. I don’t remember, we studied this phenomenon in childhood at biology lessons, because of the prescription of years and due to progressive senile insanity, I managed to forget a lot. and the water slowly leaves:

Spruce is the most suitable tree for draining the soil, because. its root system is located literally under the grass roots, i.e. quite shallow. Therefore, it is easy to transplant. In addition, practice shows that spruces have a high survival rate and endurance during floods / droughts. But shallow roots are also its minus - they most often fall during hurricanes. The second minus is the only tree that the bark beetle eats.

Oak is also not bad, but after many years, when it grows up, your grandchildren will curse you for it! )

Therefore, I tell you, the best option for our latitudes near Moscow is birch or pine:

- due to the lack of accurate data and difficulties in the calculation..

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#trees, #flood

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  • All about wood moisture - article BELMASH

    In the process of growth, the tree is filled with water from the ground through the roots. So it absorbs nutrients that promote development. Then, when the trunk is cut into blanks, some of the moisture remains with it. The moisture content of wood should not exceed 22%. Below 15%, it will not be possible to dry it in a natural way, since the external environment also nourishes the material with liquid. The indicator of the amount of moisture affects the properties of wood, how it will behave during processing. Too much water leads to mold and rot.

    Natural Moisture

    The indicator is used to determine the amount of water inside the trunk immediately after cutting or during growth. It determines the quality of drying wood materials. The natural moisture content of wood is considered the initial value, on the basis of which they begin to conduct calculations for the drying of the material. If the indicator is determined incorrectly, there is a risk of under-drying or over-drying of the lumber.

    What percentage of water is contained in the trunk is determined by the following factors:

    • structure of wood;
    • porosity;
    • environment.

    The natural moisture content of wood ranges from 30 to 80% and varies depending on the type of material. They are repelled before determining the optimal drying mode to achieve the desired quality of the dry workpiece.

    Breed Humidity, %
    Cores Sapwood Medium
    Birch - 70-90 78
    Oak 50-80 70-80 70
    Spruce 30-40 100-120 91
    Larch 30-40 100-120 82
    Aspen - 80-100 90
    Pine 30-40 100-120 88
    Ash 35-40 35-40 38
    Fir - - 101
    Cedar - - 92

    Hardwoods have a lower natural moisture content than softwoods. It has to do with the structure of the wood. Spruce contains up to 90% moisture, fir within 92%. For comparison, ash wood has only 36%. In addition, the percentage of water in the material is affected by the state of the environment. In winter, plants go into “sleep mode” and practically do not consume nutrients from the ground. Therefore, the humidity in summer is much higher than in winter. Also, in freshly cut wood, the percentage of moisture is much higher than in old blanks.

    The task of those involved in the processing of lumber is to reduce humidity to the lowest possible percentage. This is done to ensure that the workpieces have acquired the necessary hardness and strength. The wear of products whose material has successfully passed the drying process is significantly lower.

    Humidity also affects the size of the blanks. The more the material dries out, the smaller it becomes. Proper drying should be organized in such a way that moisture evaporates evenly. Then the weight and size of the workpiece will be standard, and the material itself will acquire the necessary properties. The latest methods of drying wood reduce the percentage of moisture to 6. This indicator also depends on the species, structure of the tree, season.

    Hardly dried wood is not used for construction as it may crack. The amount of water in the material for these purposes is reduced in the following ways:

    • Self-drying. A ready-made cut of natural moisture is purchased, and stacked on the site. Between the rows of boards, gaps are made with the help of bars so that air circulates freely. The support must be placed at least 1.5 meters apart, and the material will not bend. To prevent rain or other precipitation from spoiling the wood, the structure is covered with a film or roofing material from above. Natural drying is best done in the warm season. Materials are placed in the shade, under a canopy. Thin boards will dry faster than thick boards. The design is installed on gaskets made of coniferous branches or protective material.
    • Purchase of finished material. In this case, the seller has already prepared the boards and dried them naturally on his own.
    • If it is required to reduce the amount of moisture to 15% or less, then chamber drying is used in a closed room. Such materials will cost more, as processing will require a large expenditure of resources. And for construction, it is better not to use such wood, it can crack.

    The ideal use of dry wood is furniture and home decoration.

    Equilibrium moisture content

    In order for lumber to be stored for a long time and not rot, it must be properly dried. To carry out the procedure, you will need an indicator of the equilibrium moisture content of wood. It is achieved by a long stay of lumber in a certain external environment. When external conditions change, the equilibrium humidity also changes.

    Equilibrium moisture content of wood under different temperature and humidity regimes of winter houses
    Month Outdoor In winter houses
    Air temperature, С Air humidity, % Equilibrium moisture content of wood, % Air temperature, С Air humidity, % Equilibrium moisture content of wood, %
    April 8. 8 59 11.4 5.9 79 15.7
    May 17.0 49 9.3 8.3 86 16.7
    June 20.6 53 10.0 10.5 92 21.0
    July 18.0 54 10.3 12.4 90 20.9
    August 16.4 69 13.1 11.6 87 19.5
    September 14.3 72 13.0 11.8 84 16.1
    October 6.3 63 9.0 5.9 68 11.6
    November -4.1 85 17.4 -4.1 65 10.6

    Excess moisture in the rock negatively affects the condition of the finished product and spoils the blanks. Lumber under the influence of water becomes moldy, a fungus starts in it. The wood structure is porous and absorbs moisture easily. It is also easy to get rid of it, decreasing or increasing in size. As a result, with incorrect calculations of the indicator, some sections of the wooden structure may begin to bulge or settle over time. And then, under the influence of the external environment, they will again smooth out.

    Coniferous and hardwood species differ in moisture content. For a clear sorting of lumber, it is divided into 3 degrees according to the percentage of water in the composition:

    • Raw wood. Contains more than 35% moisture.
    • Semi-dry. In the range from 25 to 35%.
    • Dry. Less than 25%.

    Below is a table of equilibrium wood moisture content depending on temperature and relative air humidity:

    t, C Relative air humidity, %
    35 40 45 50 55 60 65 70 75 80 85 90 95 98
    0 to 5 7. 1 7.9 8.7 9.5


    11.3 12.4 13.5 14.9 16.5 18.5 21.0 24.3 26.9
    10 7.1


    8.7 9.5 10.3 11.2 12.3 13.4 14.8 16.4 18.4 20.9 24.2 26.8
    15 7.0 7.8 8.6 9.4 10.2 11.1 12.1 13.3 14.6 16.2 18.2 20.7 24.1 26.8
    20 6.9 7.7 8.5 9.2 10.1 11.0 12.0 13.1 14.4 16 17.9 20.5 23. 9 26
    25 6.8 7.6 8.3 9.1 9.9 10.8 11.7 12.9 14.2 15.7 17.7 20.2 23.6 26.3
    32 6.7 7.4 8.1 8.9 9.7 10.5 11.5 12.6 13.6 15.1 17.0 19.5 22.9 25.6
    40 6.5 7.2 7.9 8.7 9.5 10.3 11.2 12.3 13.6 15.1 17.0 19.5 22.9 25.6
    45 6.3 7.0 7.7 8.4 9.2 10.0 11.0 12 13.2 14.7 16.6 19. 1 22.4 24.7
    50 6.1 6.8 7.5 8.2 8.9 9.7 10.6 11.7 12.9 14.4 16.2 18.6 22.0 24.7
    55 5.9 6.6 7.2 7.9 8.7 9.4 10.3 11.3 12.5 14.0 15.8 18.2 21.5 24.2
    60 5.7 6.3 7.0 7.7 8.4 9.1 10.0 11.0 12.1 13.6 15.3 17.7 21.0 23.7

    With natural drying, the figure is reduced to 30%. In this case, the dimensions and mass of the material change. To speed up the process, technologies are used that make it possible to reduce it to 7-18% in a short period.

    Free and bound moisture

    When a tree is felled and stored in a warehouse, moisture is evenly distributed along the trunk. Before this happens, a sufficiently long period of time must pass. Immediately after the saw cut, the humidity is increased, reaching an average of 60%. Moisture inside the trunk is divided into:

    • hygroscopic (free), which is retained in the fibers;
    • capillary (bound), contained in plant cells.

    During the drying process, only free moisture comes out of the trunk. The capillary remains. It is only about 23% in wood. If the lumber was cut recently, then the moisture will be distributed unevenly along the length of the trunk. The highest percentage is observed in the butt, the closer to the top, the lower the percentage becomes. There is also a dependence of the amount of moisture in wood in some species on proximity to the core. In some, it increases when approaching the core, in others, on the contrary, it decreases.

    Table of lumber moisture values:

    Wood type Moisture index, % Comment
    Wet Over 100 Purchased if the material has been in water for a long time.
    Fresh cut 50-100 Tree felled recently
    Air dry 15-20 Typical for material that has been exposed to air for a long time.
    Chamber dryer 8-12 Lumber has been in a heated room for a long time
    Absolutely dry 0 Wood dried in a special machine

    When water is distributed evenly throughout the wood structure and does not exceed 15%, this is called standard moisture. In this state, the workpiece can be used for processing and preparation for work (finishing, construction). The material is well stored, but susceptible to weather conditions, during precipitation it can get wet and the moisture indicator will change.

    For the production of quality wood, both concepts (standard and equilibrium moisture) must be used. It must be understood that when the finished product is used outdoors, under the influence of different temperature conditions, its properties may change. Therefore, the product must be protected by impregnation.

    Saturation point of wood fibers

    This is an indicator of equilibrium moisture at which free moisture from the wood has already evaporated, but capillary moisture remains. The percentage of moisture at the saturation point ranges from 23 to 30. It depends on the type of wood, external conditions. If the indicator of moisture is lowered below this point, then the drying process will slow down, the material will begin to dry out, shift, and settle. During the natural drying process, the upper layers of the material quickly release free moisture and begin to release bound moisture. As a result, the properties of the workpiece change. This process introduces difficulties in the drying process.

    Breed Coefficient of shrinkage (Ku) and swelling (Kp) in directions
    Volumetric Radial Tangential
    Ku Cr Ku Cr Ku Cr
    Larch 0.52 0.61 0.19 0.20 0.35 0.39
    Pine 0.44 0.51 0.17 0.18 0.28 0.31
    Cedar 0.37 0.42 0.12 0.12 0.26 0.28
    Birch 0.54 0.64 0.26 0.28 0.31 0.34
    Beech 0.47 0.55 0.17 0.18 0.32 0. 35
    Ash 0.45 0.52 0.18 0.19 0.28 0.35
    Oak 0.43 0.50 0.18 0.19 0.27 0.29
    Aspen 0.41 0.47 0.14 0.15 0.28 0.30

    After reaching the saturation point of the fibers, further wetting and drying of the workpiece is no longer as important as before.

    Absolute moisture content of wood

    Physical value that represents the amount of moisture in the workpiece in relation to the amount of moisture in a completely dry material. The indicator of the absolute moisture content of wood in the calculations is denoted by the sign - W. The moisture content of completely dry wood is considered to be 0%. This value is calculated to calculate the parameters of building materials. During the drying process, the weight of lumber is constantly reduced. If the humidity in the atmosphere has increased, the indicator will begin to rise. This process is inhibited when the saturation point of the fibers is reached. At this time, the weight of the workpiece will stop falling. This state is called absolutely dry, its indicator is considered ideal and is taken as the basis for other calculations.

    Absolute moisture formula:

    W = (mc-mo)/mo× 100

    where mc and mo are the wet weight of freshly cut (mc) and the dry weight of (mo) .

    According to GOST, this concept is interpreted as simply humidity. Sometimes, in the calculations, errors occur, since the absolutely dry mass of wood, incomplete weight, is taken into account.

    Wood species Density kg/m3 Coefficient of shrinkage (numerator) and swelling (denominator), %
    at 12% humidity completely dry conditional volumetric radial tangential
    birch 630 600 500 0. 54/0.56 0.26/0.28 0.31/0.34
    beech 670 640 530 0.47/0.55 0.17/0.18 0.32/0.35
    oak 690 650 550 0.43/0.50 0.18/0.19 0.27/0.29
    spruce 445 420 360 0.43/0.50 0.16/0.17 0.28/0.31
    linden 495 470 400 0.49/0.58 0.22/0.23 0.30/0.33
    larch 660 630 520 0.52/0.61 0.19/0.20 0.35/0.39
    alder 520 490 420 0.43/0.49 0.16/0.17 0.28/0.30
    aspen 495 470 400 0. 41/0.47 0.14/0.15 0.28/0.30
    Karkas fir 435 410 350 0.46/0.54 0.17/0.18 0.31/0.34
    Siberian fir 375 350 300 0.39/0.44


    cedar pine 435 410 350 0.37/0.42 0.12/0.12 0.26/0.28
    Scotch pine 500 470 400 0.44/0.51 0.17/0.18 0.28/0.31

    The indicator is expressed as a percentage and can be calculated in the following ways:

    • based on the wet and dry mass of the workpiece;
    • using data on the amount of moisture in grams and the weight of the workpiece.

    For the calculation to be correct, practical manipulations are required.

    1. A lumber sample is cut from the workpiece.

      Moisture content of wood species

      The reaction of lumber to atmospheric phenomena, the ability to absorb moisture and evaporate it depends on the type of wood. Some trees are more resistant to moisture, others absolutely do not tolerate a humid climate and treatment with water, others quickly fill up and dry easily.

      Wood species Specific gravity (wood density in t/m3)
      Humidity Fresh 70% 25% 15% 10%
      Pine 0.82 0.72 0.54 0.51 0.47
      Spruce 0.76 0.64 0.47 0.45 0.42
      Birch 0.87 0.89 0.67 0.64 0.60
      Aspen 0. 76 0.71 0.53 0.50 0.47
      Alder 0.81 0.75 0.55 0.53 0.49
      Oak 0.99 0.99 0.74 0.72 0.67
      Larch 0.94 0.93 0.70 0.67 0.63
      Maple 1.05 0.99 0.74 0.70 0.68
      Linden 0.75 0.71 0.54 0.50 0.49
      Siberian fir 0.68 0.54 0.40 0.38 0.35
      Caucasian fir 0.72 0.62 0.46 0.44 0.41
      Cedar 0.76 0.62 0.46 0.44 0.41
      Beech 0. 92 0.89 0.71 0.68 0.64
      Elm 0.94 0.88 0.69 0.66 0.61
      Ash 0.96 0.93 0.73 0.69 0.64
      Hornbeam 1.06 1.13 0.84 0.81 0.67

      Oak and merbau are the least susceptible to changes in a humid climate. Beech and pear absorb water actively and also dry easily. Kempas has the same properties.

      Those trees that are loose in structure, which dry easily, can quickly dry out and then cracks and chips will appear on them. Dense rocks, less exposed to moisture, do not change their properties under the influence of water. In coniferous species, initially the wood is more moist than in hardwood. Moreover, the indicator grows closer to the central part of the trunk, while deciduous trees have the same percentages throughout the trunk.

      Some carpentry uses water to shape the material. This is called carpentry moisture, and its rate ranges from 6-8%. Under such conditions, the material is easier to sharpen, cut, grind, etc. Dry wood sticks together more easily, does not rot, and slightly warps.

      If the material is initially wet or freshly cut with a high percentage of moisture, it must be dried slightly before transport, otherwise it may simply not reach its destination. The transport humidity of lumber is 18-20%. Before loading such lumber and sending it by transport, it is aged on the street for about 2.5 months. To speed up the process, special drying chambers were invented, and drying was reduced to 5 days. After reaching the required indicators, the wood becomes resistant to atmospheric manifestations and retains its dimensions until it arrives for further processing.

      Methods for determining the degree of moisture

      The methods by which wood moisture can be measured depend on the type of material and the atmospheric environment. Each breed has its own measurement standards.

      The main methods for determining the degree are weight and electronic. Between themselves, the indicators may differ slightly, but the difference is not significant.

      Method 1. Weight

      To measure the amount of moisture in the sample, you will need a saw, board, ruler and accurate scales.


      1. A sample of wood is taken from the middle of the board. To do this, with the help of a saw, a piece of a small size 1-2 cm wide is cut off. Important: the sample is taken from the middle part of the board, in the center the moisture concentration is optimal. At the edges, the lumber is usually drier, since moisture evaporates from there at the very beginning of drying.
      2. The sample is cleaned of bark or other excess elements and measured on a balance. The result is recorded. For example, the value of M0 will indicate the initial mass of the sample.
      3. The sample is sent to a special drying apparatus under the influence of heating up to 100 degrees Celsius. There, the bar is dried to a completely dry state.
      4. The next checkweighing is carried out after 5 hours. The value of the mass of the sample is written as M1. Subsequent weight readings are taken with a break of two hours.
      5. It is necessary to dry the sample until the number on the balance starts to show the same value. This means that the result has been achieved and the sample has become completely dry. The last indicator is designated as MS.
      6. Using the formula:
      7. W = (M0 - MS): (MS × 100%)

        where W is the desired humidity, M0 is the first weight, MC is the last weight.

        To obtain a reliable result, it is recommended to carry out the procedure with several samples.

      Method 2: Electric

      The first method will require a considerable amount of time, since drying takes several hours, and it will need to be done many times. The electronic method is simpler, faster and requires less effort. The result will be much more accurate than in the previous method.

      In order to find out the percentage of natural wood moisture, an electrical device is used - a moisture meter. His work is based on the testimony of the resistance of lumber to electrical impulses. The presence of water molecules in the wood changes the value of the current signal and determines the percentage.

      For measurement, the needle-electrodes of the moisture meter are inserted into the workpiece opposite each other. A weak discharge is carried out through them, and the device determines the percentage of moisture present in a particular segment. For more accurate data, it is recommended to check the values ​​on several sections of the workpiece.

      The methods described above are carried out using technical devices. But mankind has been engaged in woodworking for millions of years, and earlier it was possible to determine the moisture content of wood without moisture meters.

      I had to manage on my own. Simple methods for determining the natural moisture content of wood:

      1. Bend the chips in your fingers after sawing. If it springs back and straightens up, then the tree was damp. If it turns into crumbs - dry.
      2. Hit the trunk with a heavy wooden stick. Damp wood will respond with a dull sound. Dry has a thin and sonorous “voice”.
      3. You will need a simple pencil. At the end where the tree has just been cut down, draw a line with a pencil. Material with high humidity will cause the line to turn blue after a while, dry material will leave it as it was.
      4. Dry lumber ends are cracked. Wet does not allow this.
      5. If you run a sharp metal object over a log, it will leave a scratch. With dry material, it will remain dry.
      6. When working with a hand saw, a dry log begins to crumble, and a wet one lets water into the cut. Both options are not suitable for cutting.

      Determining the moisture content of wood at home is quite simple, but it is almost impossible to achieve an accurate indicator without a moisture meter.

      Traditional methods for determining the moisture content of wood include the following:

      • By the color of the wood. A dark shade and boiled resin at the site of a fresh cut indicates that the tree is dry. Light shade and - high humidity.
      • Feel. The surface is hard, splintery, the weight of the board is light - it means dry.
      • With a drill. Drill a hole 3-4 cm deep in the sample and hold the drill in it for a few seconds. If it smokes - the material is dry, nothing happened - the average humidity. And if chips appear from the hole - wet.

      State-of-the-art wood moisture meters provide accurate and fast results. They are divided into needle and non-contact. They are configured to work with different types of wood (multimer), they are small in size and can easily fit in a pocket. Some are able to measure the moisture content of bulk material (chips, sawdust). With the help of instruments, measurements are taken by large woodworking companies that need to control the process at all stages.

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