This year I had the opportunity to see how the root depth provided by a pot affects plant size. There is a huge difference in the size of the squash plant I removed from its shallow planting and placed in a TubTrug with 4 to 5 inches deeper soil.
The squash plant in the foreground was not given more room for its roots until just before I took the picture. Look at how much smaller it is.
Gradually increasing pot size
Many nurseries advise planting in relatively small pots, then increasing pot size every year or so. For me, hampered by having to use a walker, it’s hard to repot a large plant. So, I called a horticulturist to ask what the thinking was.
Initially the horticulturist told me that the plants like it better that way. But, I said, surely they can’t tell what size pot they are in. The horiticulturist agreed. She said the underlying reason was that a small plant that likes to dry out between waterings could more easily get root rot in a large container.
That made sense. I had recently repotted one of my kumquats, and found that the soil was a lot wetter deeper in the pot than I had imagined. So, although the top of the soil looked relatively dry, a little deeper in the soil was saturated, which is not ideal for kumquats or citrus in general, not to mention avocados which abhor wet “feet”.
Deep vs Shallow roots
I would like to grow a mango. I get so hungry for fresh fruit, especially during the winter. (I’m housebound.) But mangos have both a tap root, which goes deep, and shallow feeding roots.
The largest TubTrug I plant in has nearly a 24″ top, but is about half the height of a Fiskars 24″ pot. The Fiskars pots are easy to roll around on trolleys, until I want to get them over the threshold if the night temperature threatens to drop.
Worse, however, from a visual point of view, is that they take up so much space on my deck and block a view of other plants.