Plants purchased in containers at a garden center may look fine in the store, but there are usually some that have become root-bound—with dense roots that are tightly packed into the container. You might think that a plant with lots of dense roots is a better choice than a plant with sparse roots, but this is actually not the case. If the problem is not corrected before planting in the garden, a root-bound plant often just keeps developing its roots in a tight circular fashion and never sends those roots out into the surrounding soil. This can hinder good growth habit and even cause the plant to eventually choke itself. A much better choice is a plant with a loose root ball, with plenty of loose, bare soil around the roots.
Identifying a Root-Bound Plant
Before you buy a plant, turn the plant over and examine the bottom of the container. If you see roots poking through the drainage holes, chances are good that the specimen is root-bound (the condition is sometimes known as being pot-bound). Severely root-bound plants may even be hard to remove from the pot since the roots can be firmly entwined through the drainage holes.
It is also perfectly fine to inspect the root ball by sliding the entire plant out of its container. Knowledgeable gardeners do this all the time when shopping for plants, both with potted herbaceous plants and even small shrubs and trees. Garden center personnel have no problem with this, provided you don't damage the plant while you inspect it. Simply grab the plant by its main stem between your thumb and forefinger and lift it up while tugging downward on the pot. You only need to extract a few inches of the root ball to know whether the plant is root-bound. If you see a dense mass of white encircling roots around the edge of the soil, this is not a plant you want to buy. This kind of root ball may easily slide out of the container in a mass of white roots formed into a hard ball. A plant becomes root-bound for a number of reasons, none of them good ones. The specimen may have been neglected—the extreme development of roots may be a response to not getting enough nutrients or water as the plant was growing.
The ideal specimen will reveal a few white roots exposed around the perimeter of the root ball, with plenty of dark soil also visible. The root ball may begin to crumble slightly as you extract the root ball from the container. This is an ideal specimen to buy.
How to Fix a Root-Bound Plant
Ideally, there are enough choices of a given type of plant for you to inspect several specimens until you find one with the ideal root structure. If your choice is limited to the one root-bound plant available, there are ways to improve the chances of success in the garden.
Untangle the Roots Before Planting
You can start to help the plant recover by untangling the roots with your fingers before planting. If you can tease the root-ball into a loose bundle of hair-like roots bristling out from the plant, these roots will more easily find their way into surrounding soil once you plant the specimen in your garden.
Cut Slits in the Root Ball, If Needed
If the roots resist untangling by hand, you can even cut slits into the root ball with a knife or sharp garden trowel. Most plants are quite tough, and by severing the roots you make it easier for the plant to send new roots out into the surrounding garden soil. Some gardeners slice the root balls as a matter of course whenever planting a specimen, no matter if it is a mature shrub in a gallon container or tiny seedlings in a bedding plant six-pack. Make a series of vertical slits along the sides, then slice a deep X in the bottom surface of the root ball before planting. With small six-pack plants, it's usually enough just to slightly tear at the root ball with your fingers before you plant each one.
Shrubs and trees are particularly vulnerable to becoming root-bound since they are often grown in pots for several years until they are mature enough to be placed for sale. These larger plants are often expensive and represent an investment for the homeowner. If you plan to do your own landscaping with these larger plants, follow planting instructions and make sure the roots are divided well and spread out in the planting hole. A little extra effort starting out can save time and another trip to the nursery for a replacement.