Are All Transplant Containers Created Equal?

Transplant containers serve to hold the soil and roots of the transplant in a nice, tidy package, but they fail to allow for the production of the kind of roots that help transplants recover quickly from the shock suffered when you remove them from the containers to plant them out. To the original designers of planting containers, roots were roots. Surprisingly little has been done to improve containers since those first designs. Yet the container makes or breaks the transplant.

The success of transplanting depends heavily on causing little or no damage to the root system. However, a second key point overlooked by early container designers is that root balls need to have many, healthy feeder roots on their surface. These feeder roots, essentially smaller roots with fine hairs, are extremely important to producing the best-ever transplants. You see, feeder roots are the part of the root system through which the plant takes up water and nutrients.


Plant scientists call such roots root hairs. You can find these small root hairs near the tips of actively growing roots. To the eye, root hairs give the root tip a fuzzy, white appearance. If a transplant has an extensive, fuzzy covering of feeder roots on the root ball, all the better. Feeder roots, being tiny and delicate, are good indicators to use in assessing root ball damage. If root hairs are present on the root ball when you remove it from the container, you know you have an undamaged root ball that will recover quickly after transplanting. Also, the feeder roots respond rapidly to water and nutrients in the starter solution, so the plant is off and running quickly. The fuzzier the root ball looks, the better the roots soak up water and nutrients from the soil.

The location of the feeder roots is also critical. If the feeder roots are not on the surface of the root ball, but mostly concentrated inside the root ball, the response of the transplant to planting will not be as good. The reason the transplant does not take as well as one having surface feeder roots may not be obvious but should become clear after our explanation.

If you've grown your own transplants in the past, you know that the soil in your garden differs from the material in which you grow your transplants. Mixtures for growing transplants are put together for one main purpose, that is, to produce better transplants than would soil. Therefore, these transplanting materials drain well, have excellent aeration, and are often rich in organic material. They look, feel, and weigh differently from the soil in your garden. Doesn't it follow, then, that when you put the transplant root ball into the garden, you join together two materials with different textures - soil and transplant growing mixture? Because of this texture difference, these two materials don't mesh together as soil to soil would. It's essentially like trying to mesh together two zipper tracks with different teeth spacing; they just don't go together. Scientists call the place where the two textures meet an interface.

Now let's add another element to the picture. Moving water seeks out the easiest path. Anyone who has a leaky basement will agree with this observation. The easiest path through the soil and the transplant root ball is at the interface. Many spaces and gaps in this area speed the water right on by; therefore, water and nutrients tend to flow over the root ball and spread out under it; less water actually enters the root ball. If the feeder roots are at the junction of the two soils, that is, the root ball's surface, they are in the water pathway. Their location, then, is ideal for gathering water and nutrients in the few critical days after the transplanting operation. Such surface-rooted balls give you a transplant that shows little or no wilting and rapid development in the garden.

Surface feeder roots promote not only initial growth but also later growth. Transplants lacking surface feeder roots, when dug up at the end of the season, tend to show poor root balls. Roots are small and show very little outward spread from the original root ball. On the other hand, our transplants with lots of external feeder roots exhibit much larger root balls and greater spread. Better leaf and stem growth and higher yields go hand in hand with the bigger root ball. Such results are sure to bring smiles to gardeners' faces.

A similar, confirming situation is familiar to those of us who have planted container-grown shrubs and trees. To encourage root development outward, the gardener quarter-scores the root ball. Failure to do so usually results in a poorly developed shrub or tree that never reaches its potential, or even worse, dies. Upon digging up the shrub, the gardener would find limited development of the root system.

How does a gardener encourage feeder roots to form at the root ball surface? The answer is localized aeration, which translated means, give them air! Roots require oxygen to survive and to grow. Without oxygen, such as in over-watered soil, roots rot and die. They literally suffocate. Plants specifically need oxygen for a process called respiration, which is essentially the breakdown of food to supply energy for plant development. Roots tend to grow through the pore spaces in soil; the feeder roots form at the growing tips of roots where oxygen, water, and nutrients are present. In conventional containers, air enters through the surface of the growing mixture and spreads through the mixture. The roots in the center get first crack at using the air while they grow. By the time the air reaches the edges, little is left for the surface feeder roots.