TO GRASS OR NOT TO GRASS

To grass or not to grass.This is the question that often faces the Johnny Appleseeds among us. Do we want to leave the orchard floor as cultivated black soil or cover it with a blanket of sod or some type of ground cover? The answer to this question can be of significant importance to the growers of prairie orchards. It is a difficult question to answer as we are faced with many variables that will affect the success of the method you choose.

Let us look at the alternatives. Keeping the area black has some advantages. It allows good moisture penetration and aeration of the soil. There is no competition for nutrients by other plant material. An area free of plant material doesn’t provide a home for mice and protects trees from rodent damage.

All of the above could be considered to be advantageous. There are some definite disadvantages to this system of management, however. Weed control becomes a big issue and must be accomplished by either tillage or chemical means. There is a tendency to till too deeply and damage the feeder roots, thus setting tree growth back. Root damage can cause the development of adventitious buds that develop into suckers off the roots. Weed growth directly under the tree cannot be reached with large equipment and must be removed by hand or trimmed back with a line trimmer. I do not recommend the use of line trimmers around the trunks of your trees unless you are extremely careful. One slip can cause the bark to be damaged and complete girdling often occurs. This is damage to the cambium layer, preventing the transport of water and nutrients in the trunk. Damage of this type will eventually cause the death of the tree. The alternative to tillage is to use chemical weed control. If this is your choice, be very selective about the chemicals you choose and apply them only as directed.

Tillage also destroys the organic matter in the soil, and unless it is replaced by mulching or some other means the soil quality will gradually diminish, reducing the water holding capacity and interfering with the uptake of nutrients by the tree. The fact that tilled soils offer no competition for nutrients and moisture is good in that it allows the trees to grow vigorously throughout the growing season. Problems can arise, however, in the late summer and fall as trees may remain in a period of vigorous growth too long. They do not harden off in sufficient time to prepare for winter. Soft, fresh growth is very tender and is easily damaged by the first heavy frosts of fall. Vigorous growth late in the season is a common reason for winter kill in trees.

Sod and other forms of ground cover also have their pros and cons. The plant material competes with the trees for nutrients and moisture. To compensate for the moisture lost to the grass it may be necessary to supply supplementary irrigation. If sufficient water can be supplied, grass will slow the drying of soil in hot windy summer days. Supplementary fertilizer becomes more important as the nutrients are depleted by the ground cover. Trees grown in an area with some form of ground cover tend to lose vigor earlier in the fall and generally go into winter in a more mature stage of growth. This is very evident when we compare our field trees to our orchard trees. The trees in the grassed orchard are completely bare a good month before the field trees show any significant leaf drop.

To maintain grass it will be necessary to do some mowing. The type of ground cover you choose can reduce the amount of mowing. In our orchard we are using a grass called Sheep’s Fescue and find that mowing is only required three times during the growing season. Sheep’s Fescue is a low growing bunch grass and does not form a solid mat of sod. Though it does reduce soil aeration and moisture penetration it does not restrict it as much as regular sod. Irrigation is still required to compensate for moisture lost to the grass.

Grass provides a winter home for mice and other rodents so it is wise to provide guards around the base of the trunk and be very conscientious about keeping the grass around the trunk short. Again, be careful if using trimmers. Grass will choke out many of the weeds that would be found in a tilled soil, reducing the amount of time spent on weed control. Weeds that need to be controlled can be removed manually or by chemical control.

The system that works the best for you will be dependent on a number of factors. What type of soil are you dealing with? Are you able to provide irrigation or are you totally dependent on natural rainfall? How much time do you have for maintenance? There is also the visual aspect - do you like the look of tilled soil of do you prefer the look of grass?

There is no one right answer to this question of whether or not to grass your orchard. Perhaps the answer lies in using a combination of both methods: leaving the area at the base of the tree black but grassing the rest of the orchard, for example. There are many possibilities and you may have to experiment a little to find the solution that works for you.

Amanda Chedzoy

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