Getting to the Root of the Problem

If you have a plant that isn't growing, the problem may be under the surface. (malshkoff/Shutterstock)

Q: I plant my annuals and perennials the same way, and some plants flourish while some just sit there. What am I doing wrong, and can the problem be fixed after the plant is in the ground? For instance, I planted six tomato plants at the end of May, and though their color is fine, two of them haven’t grown an inch. They get plenty of light and water, but something is wrong.

A: This is a fairly common problem. It can have several causes. The most common is that the roots are having problems. It is easy to look at the top of the plant to see if there are insect or disease problems. You can also tell if the plant is planted in the proper setting for light, heat, and drainage. The problems that we can’t see are underground.

Plants maintain a balance between their top and bottom. The plant can’t have more leaves than the roots can supply water to, and it can’t have more roots than the leaves can supply food to. Many plant problems start with the roots.

Check the roots before planting and discard or return plants with any disease, insect, or nematode problems. If there are few roots in the pot to begin with, the plant will grow slowly for a while. It will need to establish a root system in the new soil before it can begin to grow a larger top.

If there are any bad soil conditions, the roots cannot become established, and the plant will not grow. Soil in a potting mix is designed to have very good drainage and often includes specific amounts of nutrients. The new soil may be different enough physically and chemically that the roots will take a while to get out of the hole and begin growing. Once they start growing, the plant’s top will begin growing. It is best to mix the potting soil from the pot with the backfill soil so that there is a blending of the two soils. Don’t just set the root ball into the hole.

If the surrounding soil is not covered in mulch, it may dry out and the roots will have a hard time growing out into the new soil. Even good soil may not be hospitable if it is too dry or warm for the roots to grow into it.

What did you do with the leftover soil? When you have flat ground and you plant an entire pot’s worth of soil and roots, you should have a pot’s worth of soil from the hole left over. If you pile it around the top of the root system, you will be in effect burying the plant deeper into the soil. You should have leftover soil from the hole when you plant new plants. It can be used in other places or spread out over the entire bed, but do not leave it piled up on the plant roots or trunk.

Plants should be set in the hole so that the top of the soil in the pot or root ball is the same as the top of the level of the new soil it is going into. Plants that sink into too deep of a hole will not do well. The roots will not get enough air and they will die or at best slowly grow to the proper level in poorly drained soil.

If you can’t diagnose the problem visually, you may need to dig up a plant to see if you can figure out the root problem.

Dear Readers: We would love to hear from you. What topics would you like to read about? Please send your feedback and tips to [email protected].