By Robin Y Rivet, for Let’s Talk Plants! April 2022.
Should you grow your tree in a pot?
If I wasn’t addressing horticulturists: I’d simply say, “No - just burn a few hundred-dollar bills now.”
· Maybe you’re in an HOA - with only a balcony to call home for your plants.
· Are you renting and surrounded by pavement, or where planting trees is prohibited?
· Perhaps you’re a student in temporary housing but craving fresh picked fruit - imagining that a container tree could move when you do - although that seldom works out.
Admittedly a cynical optimist, I will try to address both the slippery pitfalls – and the potentials for success. Five topics come to mind that even the most experienced horticultural society members would need to address.
Photosynthesis matters. If your balcony has a height limit, is shaded, or faces north; your choice of species is limited to understory species that may survive lower-light conditions. Applying fertilizer to the potting soil will not compensate for inadequate sunshine. Depending on shade-tolerance, providing at least 3-6 hours of indirect light is a minimum expectation.
Given adequate soil volume, most trees have the potential to be vigorous, and likewise without it - often struggle. Choose slow-growth and/or small-scale species, or you’ll likely be disappointed. This means before you plunk a seedling into a pot, consider dwarf rootstocks, cultivars and graft height. One of the most egregious defects of cultivated trees, are circling or girdled roots. Guess what? Eventually, that will happen to most every tree planted in a pot. They cannot thrive for very long contained and unsupervised - without self-destructing. Purchase the largest container you can find and be prepared to lift out your tree to trim its roots occasionally. Be realistic; ultimate height and canopy size are crucial considerations.
Although modern arboriculture advises using only native soil when planting trees, containerized specimens absolutely need quality potting soil. When you do trim pot-bound roots, you should replenish the soil in your pot - that will seem to vanish every year or so. Potting mixes are typically composed of carbon-rich materials that break down over time. In effect, your tree will sink lower into its container as the organic material gets used up - until it cannot survive.
4. Irrigation Thoroughly watering tree containers is imperative, and a watering can is seldom sufficient. A steady water source will need to drench the soil thoroughly, and then allow it to dry. Repeat. Infrequently. This reduces salinity build up and dreaded hydrophobia. Mixing wetting agents and water-soluble fertilizers into irrigation water may help drainage and nutrition.
5. Pruning & Pollination If fruiting trees are your goal, realize that two varieties may be necessary for pollination, and specific pruning is often needed. Be sure your space allocation is sufficient. Prune too much, too little, or at the wrong time - and fruit won’t happen. Wind-pollinated trees might also need a breeze.
Do you want specific suggestions?
Dwarf lemon, kumquat citrus, and figs like Black Jack or Violette de Bordeaux do well in pots, but avocados seldom prosper. Arbequina olives adapt easily to large containers, but olive fruit fly may ruin your crop. Cavendish banana, jujube, Nikita pineapple guava and strawberry guava are alternative small-scale fruit trees.
Low-chill, ultra-dwarf stone fruit trees are also possible given ample sunlight, but they’re difficult to procure.
Tree-like flowering shrubs also worth considering: Brugmansia, Caesalpinia, Callistemon, Camellia, Duranta, Elaeagnus, Grevillea, Hibiscus, Iochroma, Lavatera, Leptospermum, Plumeria, Vitex. Please don’t imagine you can trim full-size trees into submission. That is an art – called Bonsai.