Planting woody plants in compacted soils

Many homeowners today are discouraged when it comes to their landscapes because many of the trees and shrubs they plant fail to thrive. If poor watering is not to blame, the issue may be compacted soil.

Compacted soil

Today more than ever, construction practices lead to severely compacted soils around new homesites. The use of heavy equipment is the main culprit. Machinery traffic over soil reduces its porosity, or open pore space between soil particles. This open space is important to plant health because water and air enter and move through the soil through pores. When these pores collapse due to compaction, the soil becomes poorly drained and air can no longer circulate though the soil. Imagine if you were a plant root in such an environment. There would be little water to satisfy your thirst and no air to breathe. Yes, plant roots need air, especially oxygen, to carry out the basic biochemical processes of life.

What can be done about compacted soils? One recommendation is called double digging or extra digging. If you are planting into compacted soils, it is a good idea to work the soil around the hole, not just dig a hole and insert the tree. How big an area needs to be worked? That depends on the size of the tree and degree of soil compaction. A minimum effort would be to dig a hole at least twice the diameter of the treeís root system and then work an additional area of soil that extends several feet around the hole. The hole should be dug deep enough to insert the plants root system without twisting or breaking roots. Remember that the plant should be growing at approximately the same depth after planting as it was when growing in the nursery or container. This can be determined from a change in coloration on the trunk. The area around the hole should be worked to a depth of 8 to 12 inches using a shovel or tined instrument such as a pitchfork. This will reduce compaction and promote healthy root growth by opening up the soil to allow water and air movement.

Compacted soil
It is usually unnecessary to amend the soil with material such as peat moss or pine bark. Rather, use the same soil that was removed from the hole to back fill when planting the tree or shrub.
Compacted soil Earthfill
Molded soil

Finally, donít forget to keep the newly planted tree or shrub well watered for the next few years, and add two to three inches of mulch to the surface of the planting hole to reduce water loss and control weeds.

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