Container Gardening


Lots of pots get bought in April. Purists favor terra cotta . …. Serene as old stone, it’s porous, promoting air circulation and moisture balance. Downside, it’s heavy and breakable. Also, chemical salts (you see a whitish streaking or crust) can build up to harmful levels. Remove by soaking empty pots in vinegar. “Clay” is the same thing, only cheaper. Terra cotta glazed on the outside is almost as healthy and looks cleaner.

Plastic is cheap, lightweight, durable, and retains moisturize. However, it doesn’t let the roots breathe and can retain too much moisture. And it’s, er, plastic. I like it for hanging vines. Clear plastic (e.g. disposable cups) is good for hanging orchids, very light and the roots get sun.

China is pretty but is functionally like plastic only heavier, more expensive, and breakable. It’s not good outdoors in winter. If you like china, use decorative “cashe pots” (e.g. no drainage hole) j big enough to fit a clay pot holding your plant, with some gravel underneath for drainage. Ferns, particularly, like double potting as it keeps their roots cool and damp.

Outdoors, foam containers are lightweight and good insulators but the styles tend to be too ornate. Wood’s good but can rot over time unless treated with chemicals (potentially very dangerous). Concrete planters are wonderful but very heavy. In the right place, plastic’s OK too. Reduce weight and increase drainage and insulation by filing the pot’s bottom with Styrofoam packing “peanuts”. Black pots, of course, absorb more heat than light ones.

I like terra cotta indoors and out. My secret: terra cotta’s most likely to break by freezing in its first winter, so get “pre-tested” pots by buying last year’s stock in early spring from nurseries that store their pots outdoors. When a pot breaks, use “Quick Grab” glue or tie it together with decorative string.

Whatever pot you’re buying, make sure it has a drainage hole. And size matters: don’t pot up more than an inch or two in diameter at a time. Overwatering in the number one houseplant killer and over-potting is a key cause of overwatering.

Aesthetically, make your pots a consistent part of the décor. Use similar color, shape, material, and/or size to unify groupings. Pick size, shape, and color to compliment the plant. (Some people have lots of shoes; I confess to a closet full of pots but often still don’t have just the right one.)

Winterizing Container Plants

“In My Garden” is Braveness, my little Japanese Maple tree, just before moving into his winter home — a cold frame made out of two orange crates covered in bubble wrap. In the background are ivies under-planted with spring bulbs that will stay out all winter as is. Some people are surprised that I have year-round outdoor plants on a balcony but

any plant that will survive in the ground year-round in your hardiness zone can also survive in a container with a little help.

Temperate-climate plants like Braveness die in the house; they need summer sun and winter domrnacy. In winter, the sleeping plants need protection against short–term temperature fluctuations but must also have circulating air and just enough moisture to stay alive but not rot. A plant that keeps its leaves through the winter also needs light.

Insulators: There are many ways to insulate container pots. Generally you either wrap the pot with an insulator like bubble wrap and/or place it in a cold frame or unheated garage. A couple of inches of bark chips or other sterilized mulch on top of the soil helps too. It’s good to keep the pot off the frozen ground — elevating it on wooden slats is ideal. As a rule of thumb, pots over 14”in diameter can be left outside without protection other than two or three inches of top mulch. (Note to Maureen and Kim: I won’t try this in Canada!)

Water: A dash of water should be added every week or so to replace that lost to evaporation but be very careful. The right watering balance in winter is tricky. Both over- and under-watering can kill the roots

Air circulation:The wrapping or cold frame should have small openings at the top and bottom to allow air movement. Likewise, top mulch should be loose and airy. An open bottom also assures drainage.

Pots: Almost all types of pots can stay outside. However, most pots can be broken by the expansion of excess water freezing into ice. The best way to prevent breakage is to remove the saucers before first frost and to elevate the pots so that all excess water drains away. If the pot cracks anyway, wrap heavy string around it several times to hold it together. The band of string then adds a decorative element.

Sub-zero temperatures:Braveness likes a cold winter – temperatures in the 20’s and 30’s are fine but below zero temperatures can kill him. I live in a zone 6, so our winter temperatures rarely fall below the teens. However, it can happen. The cold frame will insulate Braveness from the extra cold for a few days. If a longer cold snap is predicted, I wrap several extra layers of insulation around him before the temperatures fell and hope for the best. If necessary, as a last-ditch effort, I’d bring the whole cold frame indoors for short periods – just enough to warm it up to 20F and back outside before defrosting occurs.