Summary: Many believe the absence of sunlight is the only problem of shade. Of equal or even greater importance is the lack of moisture and plant nutrients resulting in part, at least, from unfavorable soil conditions.
Question: The grass does not grow in the shade under our trees. What part does soil play in the grass growing – or is it all from a lack of the grass getting enough light.
I need your help to make our lawn look better – none or thin grass in the shade is the next landscaping problem we are trying to solve. Stacy, Conway, Arkansas
Answer: Let’s look at the issue of soil conditions and growing grass in the shade.
The enormous water requirements of trees is one reason for the lack of a sufficient moisture supply for the grass. Another reason, strangely enough, is the direct result of an excess of moisture during certain seasons of the year.
In late winter and early spring practically all lawns receive and hold too much water unless they are well drained.
If this saturated condition lasts very long it does considerable damage to grass, directly.
By keeping much needed air from the grass roots, and, indirectly by causing a “puddled” soil. The unfavorable effects of keeping oxygen from grass roots is apparent but the puddling damage requires some explanation.
Texture and Structure
All soils are composed of particles of varying sizes. In one gram of very fine sand there will be approximately two million particles while in the same amount of clay there would be about forty-five million particles – more than twenty times as many.
The size of particles in a soil determines what is called its texture.
These particles have a certain arrangement.
In some soils, each particle acts as a separate unit whereas in other cases various minute particles become grouped together so that groups act as single units. The arrangement of soil particles is called its “structure.”
These mechanical characteristics are of great importance in determining the moisture movement in soils. The best turf soils are those having a “crumb” structure.
Where many small particles are grouped together to act as a single large unit such a crumb structure permits easy and rapid movement of air and water, at the same time presents a condition where the optimum moisture supply is retained.
Soil “puddling” occurs in the heavier soil when small soil particles are forced or floated in between larger particles.
Thus the soil becomes more compact and at the same time plastic. The potter works clay to break down the crumb structure to make it plastic so they can mold it into any desired shape.
Heavy soils become compact and tight because of excessive moisture or of having been worked when wet. In the case of soils under trees, these remain wet until late spring because evaporation is slow.
This means that the soil gradually becomes more and more compact until in late spring there is a heavy, gummy mess.
Sooner of later, this soil under trees will dry out. It will dry very fast with the advent of warm weather coupled with the scant rainfall that reaches such soils in summer.
As the soil loses so much water its volume shrinks greatly, making large cracks in the lawn.
These in turn cause a great loss of moisture from the subsoil by evaporation.
So the condition is continually aggravated until by midsummer both tree and grass are suffering acutely from moisture shortage, unless drastic measures are taken to prevent this situation.
Mere artificial irrigation during dry weather will not provide much of a remedy.
Temporary improvement may follow the use of enormous quantities of water but in the end it will only aggravate the unfavorable soil condition.
It is not possible to describe in this article all of the steps necessary to overcome a puddled or unfavorable soil.
One of the principal factors involved in improvement of compact soils is provision for adequate surface and underground drainage.
The former can be taken care of by surface grading while the installation of drainage pipe is about the only means of improving underground drainage.
Friable Soil Needed
At the same time a friable, loamy top soil should be installed, if possible. Extremely sandy or clay soils will never support good turf.
Heavy soils should be broken up with coarse sand and a liberal supply of organic matter. This furnishes a home for the needed friendly bacteria, and retains moisture and plant food.
A sandy soil may be made more compact by adding soil of heavier texture and also incorporating enormous quantities of organic materials.
Given a fairly suitable soil, the moisture problem of tree-shaded lawns can be solved. Water should be applied infrequently during drought in the form of a medium fine but long continued spray.
The soil should be thoroughly soaked to a depth of five or six inches. No definite period of watering can be prescribed because of the many variable factors.
However, a lawn cannot be considered as having been properly irrigated unless an actual examination shows the water to have penetrated six or more inches into the ground.
It does not take any more water to give a lawn a good soaking once a week than to give it daily light sprinklings.
Summary: Growing grass in shade, is a challenging condition to grow a lawn. Now we’ll look at several conditions which can prevent grass from growing well in shade.
Question: Nothing we do seems to help grass grow in the shade under our trees.
We have tried watering more, putting in special grass “designed for shade” and put more fertilizer down, but nothing seems to help. What else can we try, as we are just about to give up on the shaded grass project! Dale, Johnson City, TN
Answer: Dale, failure of grass to thrive directly adjacent to tree trunks may be the result of the heavy wash of water down tree trunks during rains.
This is particularly noticeable in winter. The excess water collects in pools at the base of the trunk and may smother the grass, at the same time puddling the soil.
Such a condition may be overcome by mounding a shallow layer of soil at the tree base to provide immediate carry-off of the excess water. This soil mound should not be deep enough to smother the tree roots.
Another solution is to have a cultivated area at the base of the tree, extending out four or five inches.
This should be of fairly light soil which will permit ready absorption of water. This treatment is suitable only for use around medium sized trees.
Rainfall adds still another difficulty in that water collects on tree limbs and falls to the ground in large drops. These tend to wash away the soil and expose the grass roots.
This is particularly bad in winter when such exposed roots will be subject to severe heaving. Nothing can be done to prevent falling of these large drops.
However, if a lawn under trees is built and maintained properly the turf developed should be sufficiently thick and solid so that the large drops will not wash the soil.
Soil Often Toxic or Acid
There are still other unfavorable soil conditions that may interfere with growth of grass under trees.
For example, the soil may be extremely acid or may contain toxic substances which have been exuded from tree leaves and washed into the soil. Extremely acid soils are improved by liberal applications of garden lime.
However, a soil test should be done before lime is added. Lime is not advisable to use unless it is actually needed.
An ordinary surface application of lime does little good as the lime is washed off before any benefit results. The lime must be incorporated into the soil.
Many folks think an early spring “whitewash” of their lawns is necessary. Actually it may do more harm than good because too much lime encourages certain types of weeds.
Certain Bacteria Essential
Enormous quantities of certain types of bacteria must be present in soils if they are to support a good growth of grass.
These bacteria break down soil organic matter into humus, at the same time liberating certain chemical food elements to grass roots.
So often soils in shaded areas are very unfavorable to the development of soil bacteria.
They may be water-logged during winter and early spring, and excessively dry in summer. Or, the soil may be extremely acid. An unfavorable bacterial environment is another cause of lawn failures in shady places.
Remove Leaves When They Fall
After good turf is established in shade, care must be exercised to prevent losing it when leaves are falling. They should be removed promptly else the grass may be smothered.
It is a mistake to place leaves or other materials over grass as a winter covering. They do more harm than good. To keep them from harming grass, leaves should be removed at least once weekly.
Certain kinds of oaks and other trees hold part of their leaves all through the winter. This means that some of them are falling during winter months, particularly during heavy rains.
If these are not removed frequently they will become packed down against the ground, sometimes even becoming frozen, and thus smother grass in spots. By spring the lawn may present a sorry sight.
As with other phases of the shade problem, a sturdier stand of turf will be better able to withstand smothering. The turf will hold up the leaves and prevent their packing against the ground.
Problems Of Shaded Lawns – Hot Weather
Summary: Hot weather can cause lawn problems for grass growing the in sun, but it can also cause issues for grass growing in the shade.
Question: Last summer the hot weather hit our grass really hard even the grass growing under the trees in the shade. What steps can we take for our lawn this summer if we face high temperatures again? Keith, Huntsville, Alabama
Answer: Keith, summer heat can really push a lawn and the grass that makes up a yard to its limits. This is not limited to grass but high temperatures also affect plants in the landscape.
The hot temperatures and weather conditions of summer can bring other lawn problems front and center. Those who have shaded lawns to battle generally think theirs is the worst burden.
True enough, the growing of grass in shaded conditions is quite a problem, but there are certain compensations. For one thing, very few weeds will grow in the shade; crabgrass not at all, and dandelions to only a limited extent.
Then, too, shaded lawns are favored by being protected from the ravages of the burning sun that destroyed so much turf in open places during the past summer.
In contrast to the usual conditions shaded lawns came through the summer in much better condition than ordinary lawns.
Flagstone Terrace Option
One reader brought us an interesting problem regarding treatment of a lawn area around a tree.
As this particular place in his yard received a lot of wear he was considering putting down a flagstone terrace on the area with grass between the stones and wondered if this would be injurious to the tree.
We immediately took up this problem with a tree professional who replied as follows:
I see no objection to the method of treatment of the shaded place brought up by your reader. This would certainly be preferable to an all concrete covering over the surface of the soil occupying the tree roots.
The crevices between the stones should be fairly effective in allowing for entrance of air and water to the tree roots and would also permit of the application of fertilizers to the tree roots by some modification of the perforation system which we recommend.
From the standpoint of the tree, it would probably not be any more harmful than a heavy covering of grass.
Some other interesting emails we’ve received on growing grass in shade articles.
Growing With Light Sandy Soil
There are some who think it is easy to grow grass in the shade if they have a light sandy soil with which to work. This is in line with the importance of the lawn soil condition.
It is better to have a soil that will not puddle. Clay soils will, but sandy soils will not.
Growing a lawn in the shade, here’s my opinion.
From my many years of experience I would think it is fairly easy to raise a lawn in the shade in sandy soil, but very hard in soil which is mostly heavy or even clay.
The use of shady grass seed only will not make a permanent lawn. Where there is shade and sandy soil the top soil should be well fertilized every spring and fall, plenty of perennial grass seed put in with a heavy mixture of Fescue.
It is very important, that not much watering and especially not to cut the grass too closely during the summer months. Where there is heavy soil and lots of trees, etc., the best way is to put a heavy layer of sand or gravel under the surface.
There surely will be good results if the surface consists of only two or three inches of good well fertilized light top soil; and, remember, not much watering during the summer, possibly once a week will be plenty.
I’m not so sure three inches of topsoil over a layer of sand or gravel would be sufficient.
It seems to us that a minimum of six inches should be provided. Otherwise there would hardly be enough of a moisture and food retaining layer.