Can I plant a tree or shrub where a pine tree was just removed or will the soil be too acid? This is a question I seem to be receiving more often. Maybe because so many Scotch pine trees are dying from pine wilt and people are planning to replant the bare area.
Whatever the reason for the increase, the idea that pine needles will make a soil too acid is a myth. While pine needles themselves are acidic, plants do not have the ability to change the pH of the soil they are growing in. Sure would be nice if they could.
Soils in our area tend naturally to be alkaline. This is due mainly to the limestone parent material from which Great Plains soils were formed. The removal of topsoil during construction and replacement with subsoil, use of alkaline building materials and high pH irrigation water also contribute to alkaline soils.
It seems to make sense that if pine needles are acidic, then over time they would lower soil pH or make it more acid. However, research conducted on surface mulch has shown that it has little effect on soil pH.
If mulch, like pine needles or sphagnum moss, were incorporated into the soil, over time they may result in a slight lowering of pH. However, in most cases, the use of high pH irrigation water is likely to counter such effects.
Go ahead and plant where a pine tree once grew without worrying about the soil being too acid. Since most plants prefer a slightly acid soil, with a little luck, the pH might be a little lower in that area.
Another question related to planting new trees where another tree had been planted is how close to the old stump can the new tree be planted? There seems to be a myth that new trees cannot be planted too close to where another tree had been planted.
If the old stump has not been ground out and the plan is to let the stump decompose naturally, the new tree can be planted as close to the old stump as it is feasible to dig a wide (six to 12 inches wider than the new trees root ball), but not too deep of a planting hole.
It may be easier to dig the new planting hole four or five feet away from the old tree stump. Old, large tree roots can make digging more difficult. If it is preferred to plant the new tree as close to the old stump as possible, an axe may be needed to remove old roots to be able to dig a wide enough planting hole.
Ideally, the old stump would be ground out and the soil allowed to settle before planting the new tree. Waiting for the soil to settle helps prevent the new tree from settling too much after planting and end up being planted too deep.
Be sure to keep the wood chips from the ground out stump and use these as mulch around the new trees. Just be sure the mulch layer is only about four inches deep and not piled against the trunk.
Kelly Feehan is a UNL extension educator-horticulture. Reach her at (402) 563-4901 or by email at firstname.lastname@example.org.