How to control weeds around fruit trees

and mowers and string trimmers can damage the trunk.

Fruit trees thrive along the Wasatch Front and in many other locations in Utah. Backyard fruit trees are very common in Utah, and producers quickly become attuned to insect and disease pests that can swiftly spoil substantial amounts of fruit. They are typically less aware of the detrimental effect of competing vegetation around fruit trees. This fact sheet describes the nature of vegetation competition and proposes management strategies to reduce or eliminate competition.

Weeds or grass growing immediately around tree trunks will compete with fruit trees for water, nutrients, and sometimes for sunlight (Figure 1). One experiment demonstrated that grass growing near apple tree trunks delayed the onset of fruiting and reduced vegetative growth compared to trees surrounded by an area that had been kept vegetation-free with mulch, cultivation, or herbicides. Also, grasses were more competitive than broadleaf weeds. In another experiment, adding more nitrogen did not overcome the competition imposed by grass.

Grass growing immediately adjacent to fruit tree trunks poses several disadvantages. Grasses are highly competitive and will deprive fruit trees of the water and nutrients they need to thrive. Grass root systems are finely divided and are very efficient at removing water and nutrients from soils. Leaving grasses un-mowed around trees creates rodent habitat. In the winter, if populations are high and other food sources are scarce, rodents will eat the bark from fruit trees, which will girdle and kill the trees. When using mowers and string trimmers on grass immediately adjacent to fruit tree trunks, the bark may be damaged. The risk of damage declines but is not eliminated as trees age and the bark becomes corky. Thus, we clearly see that grass and other vegetation growing around fruit tree trunks is not beneficial. The next logical questions are how to make the area around fruit trees vegetation-free and how to keep that area vegetation-free. A related question is how large a vegetation-free area should be.

Research done for both apples and tart cherries shows that a vegetation-free area of between 2 to 3 feet in radius is required to eliminate the competitive effects of grass. No additional benefits were derived from increasing the vegetation-free zone beyond a 2-to 3-foot radius.

In a backyard setting, vegetation can be removed or killed. To remove grass and other vegetation, carefully and shallowly dig it out with a shovel. This is a lot of work. Take care not to damage tree roots in the process. Alternatively, the area around the trunk of the tree can be treated with non-residual herbicides containing glyphosate (Roundup®). Protect the trunk with plastic kitchen wrap or aluminum foil before treatment. Once the spray has dried, remove the wrap. Treated vegetation will turn yellow and die within two weeks (Figure 2).

Once competing vegetation has been controlled, discourage the growth of new vegetation by applying a layer of organic mulch such as wood chips or shredded bark in donut fashion around the base of the tree (Figure 3). Don’t pile mulch up around the tree trunk. If mulch is piled around the trunks of fruit trees, particularly apples on dwarfing rootstocks, the scion portion of the tree above the rootstock may send out roots into the mulch and the dwarfing influence of the rootstock is lost. Mulch has the added benefit of retaining soil moisture. Refresh mulch every few years for the life of the tree.

Keeping vegetation away from tree trunks is not just for aesthetics. Relieving competition for water and nutrients from fruit trees allows them to be more productive. This is good horticulture.

Related USU Extension Publications

Photo Credit

All images were provided by Teryl R. Roper.

Literature Referenced

• Al-Hinai, Y. K., & Roper, T. R. (2001). Temporal effects of weed control on tart cherry tree growth, yield and leaf nitrogen concentration. HortScience 36, 80–82.
• Merwin, I. A., & Ray, J. A. (1997). Spatial and temporal factors in weed interference with newly planted apple trees. HortScience, 32, 633–637.
• Shribbs, J. M., & Skroch, W. A. (1986). Influence of 12 ground cover systems on young ‘Smoothee Golden Delicious’ apple trees: I. growth. Journal of American Society for Horticultural Science, 111, 525–528.

Published November 2021Utah State University ExtensionPeer-reviewed fact sheet

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Authors

Teryl R. Roper, Utah State University Extension Pomologist, Department of Plants, Soils, and Climate

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"Weeds are the bane of my life" - There are not many gardeners who have not expressed this thought at some time or other.

The typical disaster area is the garden that is continually producing nettles, docks, ground elder, creeping buttercup, bindweed and all their associates. As k for advise and we are usually advised that we should have dealt with the problem before we planted. Quite correct but that's not much help now, is it?! How do we correct it now?

There are of course various chemical weed killers that can be used as spot treatment on larger individual weeds and clumps. If you prefer to use one of these then give your particular problem weeds to your chemical supplier and they will advise on the best choice.

If you prefer not to use chemicals then the first temptation will be to reach for the garden fork to dig the roots of these obnoxious weeds out once and for all. Hard work but effective. The problem here is that it may well ruin numbers of your fruit plants as well, particularly smaller/shallow rooted subjects such as Raspberries and Strawberries. Many of our fruiting plants produce good fibrous roots close to the surface. Not only does this digging let in drought, it ruins the root system and makes the plants struggle for survival.

The easy way is to cover almost the entire area with black polythene of a reasonable gauge [thickness]. First chop down any taller weeds to make a good level surface. Lay the black polythene out to within 2" of the base of your fruit plants and bushes. You must allow this small area to enable precious moisture to reach the roots. Cover all of the remaining area without leaving any gaps. The weeds will not grow through the polythene and will eventually die. To make an attractive finish to the area cover the polythene with ornamental bark chippings - and your problems are over.

The only other precaution is that if puddles persist then you will need to spike that area with a garden fork to allow water to drain away.

Annual weeds are an ever present problem but if we tackle them promptly they do not take hold in the same way as perennial ones do and they do not take long to control. The sec ret here is to catch them before they seed, especially those with a fast lifecycle like bittercress and groundsel. Once you see an annual weed it is time it was removed. A few minutes now can save you hours of back ache next month and remember, even small weeds are consuming valuable food and water that your plants need. Hand weeding is always best with smaller/annual weeds, especially when you are working amongst strawberries or raspberries. In-between the rows a good sharp hoe is essential. Always try to hoe lightly and before the weeds are very large. It is always better done when conditions are largely dry. If you hoe before or after rain they may simply re-root into the soil, unless you remove them at the time. When the soil is on the dry side simply moving the soil kills the weeds you have hoed and unseen seedling weeds as well; make sure they are largely left on the surface and not buried with soil again. A good sunny early morning is always the best time.

With larger areas a light hand rotovator is a real boon and can be used to make light work of the problem. Make sure you do not get too close to your plants and not more than 2" deep. The root area of the plant often spreads the same width as the head of the plant.

Grass can also be sued to good effect in larger areas and can make an effective backdrop and pathway but should not be allowed to grow too close to the trees or bushes. Always leave an area of 3' al around the plant or tree.

The ingenuity of the gardener when controlling weeds is sometimes quite remarkable. I will always remember seeing rows of fruit trees with old kitchen carpet laid out inbetween. Not very attractive but very effective - and soft to the foot too, as long as you can stand the colour scheme!