Improving Garden Soils

The most-asked gardening question I get is, “How come my plants won’t grow?”  My first response is asking whether the clay soil has been amended, and secondly if the soil has been tested.  Everything the plant needs in order to grow and reach maturity begins below the ground in that red sticky clay soil that most of us endure.

The top foot of soil is crucial to the plants as this is where most of the roots perform their best, absorbing moisture and nutrients and look for air pockets.  Plant roots need air, which is found in porous soil.  However, in our clay soil, most often there are no pores and the soils are quite compacted.  The best soil amendment to use to improve plant growth, boost plant health and performance, and improve the soil profile, is pure compost.  It is easy to dump loads of compost into a future garden space and work the soil with a tiller than it is to amend individual holes.  By amending 12” of soil with good compost, the soils will become porous and eliminate compaction as well as breaking up the clay particles. 

potting soil

By definition, compost is a make-up of dead organic material. When it’s broken down, unrecognizable as to the original ingredients, and has that dark, black color, it is compost.  A compost pile is easy to begin at home.  An ideal compost pile is made up of vegetable and fruit scraps, spent blooms, plants that have been cut back at the end of the season, grass clippings and leaves. Try to avoid composting plants that are heavily infested with bugs or diseases.

Many of us assume that leaves should be bagged or raked to the curb for the city to pick up. But guess what they do with them? That’s right – turn them into compost, and sell them back to us!

As your pile heats up, it’ll give off heat and kill lingering weed seeds.  Turning the pile with a garden fork every few weeks will help the process of decomposition go faster by increasing the temperatures in the mound as well.  Air also needs to reach what may lie at the bottom of the pile.  By bringing the bottom to the top, it works the process evenly.

The best time to amend a garden site is in spring when the temperatures begin to warm.  Warmer temperatures allow the compost to improve the soils.  If you are making your own compost pile, begin throwing your “green” waste in fall and allow the compost to breakdown at least 6 months prior to use.

If a planted bed exists and preparing individual holes is the only the task at hand, amending can still be achieved.  Dig holes twice the size of the pot the plants come in.  When digging, remove half of the clay soil and discard while breaking up the remaining portion and blending that with some compost.  Also, score the bottom and sides of the planting hole to improve drainage.  Backfill slightly with the clay/compost mix, place your loosened root ball in the hole in the center and surround the roots with more of the clay/compost mix.  When leaving clay in the mix, never keep more than 50%.  This is ideal as clay does have some benefits – such as holding water and nutrients longer during drier spells.  Also, native plants love non-compacted, enhanced native soil. 

Occasionally the question of improving soil drainage comes up.  I highly recommend applying PermaTill® to your soil mix.  PermaTill® is a baked slate rock aggregate that allows moisture to drain, adds porosity to the soils and allows root penetration.  Because the material is baked, it’ll last forever and never needs to be replenished.  An ideal mix to improve drainage would be 25% PermaTill®, 25% compost and your existing soil as the remainder portion.  Another bonus is that PermaTill® prevents critters such as voles from eating your plant roots.  PermaTill® is available locally in bulk or in 40lb bags.  For more information regarding this product, visit  Lastly, soil testing is essential, as the results can give you clues about what plants to grow, where to grow and how to improve plant growth.  One of the most important things a soil test can determine is the pH.  A pH scale goes from 1, very acidic, to 14, very alkaline. Most garden plants perform well in a slightly acidic to neutral pH of 6.2 to 6.5.  Soil test results are also important in letting you know if necessary nutrients such as nitrogen or calcium are abundant or lacking.  A North Carolina Department of Agriculture soil test can give you a full account of what is in your soil, with recommendations of how to improve it.  Every county in North Carolina has a Cooperative Extension Center that offers FREE soil tests from April 1 –November 25. A $4 fee applies the rest of the year. You can get more information regarding soil testing through the North Carolina Cooperative Extension or the NC Department of Agriculture website.  Go to

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