Musing on the under-pot zone

Have you noticed how potted plants try hard to get their roots out of the container? Potted pelargoniums, marguerite daisies and cordylines dawdle along until they get their roots into the soil underneath the pot and then they put on a spectacular flourish.

What causes this? It can't simply be that their blueprints tell them to grow their roots to a certain defined extent, because roots try to escape from very large pots as well as small ones. They must be looking for greener pastures. Perhaps the soil under the pot is cooler and moister than that inside the pot, or perhaps there are better combinations of water and air in the under-pot zone.

I am thinking about this in designing the strawberry towers mentioned in an earlier post. I would like the plants to be as happy as possible in their hanging containers while at the same time I would like them to be low maintenance and only require watering and turning every two or three days.

So I am thinking about ways to simulate the under-pot conditions that plants seem to like and ways to create these conditions in the hanging containers. My earlier designs for the hanging containers included a water reservoir (like the pop bottle planters or a self-watering pot) but now I am inclined to try a base that is filled with coarse sand (like a miniature capillary watering tray) with a top unit containing potting mix set on top of the sand. Plant roots should be encouraged to spread from the top unit into the sand-filled base.

Experiments are needed to establish whether plant growth would be better in this type of system than in the simple water well pots, and to establish whether plants would prefer the top unit to be set into the sand or suspended slightly above it, and whether sub-irrigation or top watering would be best, and whether fertiliser pellets would be better placed in the top unit or in the sand... There are lots of possibilities to try. I looked on the internet to see if anyone has done any of these experiments already. Pot-in-pot growing looked similar but I didn't find enough published information to answer my questions. I will have to find out the slow way.

Summer will officially be finished in two weeks so I had better get busy.