Home & Garden Columns

Garden Variety: More Container Planting: Material Differences

By Ron Sullivan
Friday August 31, 2007

Containers for planting are limited only by your imagination—and a few realities, what plants need.  

Their roots need access to oxygen, and that gets ignored way too often. Out of sight, out of mind, evidently. That mistake happens in the ground, too: people bury tree roots under paving or a few extra feet of soil, and then wonder why their prized tree is dying.  

Oxygen can’t get to roots when they’re underwater, a surprisingly common problem with container plants. People actually put plants into containers with no drainage holes.  

The poor plants stand in water, which despite being two-thirds oxygen can’t deliver that element to roots. The fact that one can sometimes get away with it—that infrequent watering, well-aerated soil, a very tough plant, and dumb luck come together just long and often enough—perpetuates the bad habit. 

If you have a pot without drainage and it absolutely needs a plant, as opposed to your knitting-needle collection or the cat’s drinking water, you have choices. Drill holes in the bottom, and don’t be stingy; make several and make each an inch wide.  

Too scary? Find a real plant pot small enough to fit inside, and pot your plant in that. Take it out to water it, or at least pour the leftovers out after you water.  

If you have a sunny enough spot—they’re almost always sun-lovers—and your non-draining pot is wide and shallow enough, you might adopt a carnivorous plant: a Venus’ flytrap, a sundew, or a handsome hooded Sarracenia, “pitcher plant.”  

These do well when their pots sit in shallow water; most are originally swamp or freshwater marsh plants. Use distilled water, or its “purified” equivalent.  

Unglazed clay is the best material for a plant pot. It’s porous enough to let water evaporate through it, to “breathe.” It’s also heavy, brittle, and often homely.  

Glazed ceramic pots can be prettier, and generally are at least a bit cool inside to keep roots happier. Wooden boxes and half-barrels have that virtue too, but they decay faster. Biodegradable is good, if it doesn’t involve, say, fungi that also attack roots.  

Those ubiquitous black plastic nursery cans are hard on plants. They’re meant to be temporary vehicles, not permanent homes. In plastic, it’s easier to create an anaerobic situation because the only way water can escape is through the holes in the bottom, which sometimes get blocked by roots. 

The other problem with most nursery cans is that they’re black. Black plastic absorbs heat very fast. You can cook your poor plant’s roots to death in a day when the sun’s angle changes with the season.  

If you’re stuck with plastic, at least look for tan or cream-colored cans. I’ve even seen bright pink one-gallon horrors. As you like it; I’m not playing Martha Stewart here.  

Tufa, a light porous stone, has ideal drainage and a good imitation, “hypertufa,” can be mixed up and molded.  

There’s a “Beginning Hypertufa Trough Construction” class at the Tilden Botanic Garden on Sunday, October 14, 9 a.m. to 11 a.m. $65. See to www.nativeplants.org/classes.html for a registration form. 



Ron Sullivan is a former professional gardener and arborist. Her “Garden Variety” column appears every Friday in the Daily Planet’s East Bay Home & Real Estate section. Her column on East Bay trees appears every other Tuesday in the Daily Planet.