Sun-proofing containers

In the midst of this monsoon season, persons in my household decided it was time to paint the deck with waterproofing sealant. This isn’t the best timing, but I have to admire their initiative. This meant the container plants on the deck needed to make their way to temporary quarters on the front path where it’s hotter than Hades in midsummer.

Large pots of tomatoes, begonias, pelargoniums, moonflower and morning glory vines, and several flats of annuals still yearning to be planted are currently dazed and bewildered in a suddenly brighter location. The newly painted deck wood is slow to dry, and the containers have been on the front path for more than a week.

The cooler, spa-like conditions of the back deck have made these plants tender. With no need to develop thicker skins to shelter interior tissues from ultraviolet rays, they’ve grown lush foliage and extended their stems to gather light. Now they’re reeling from full exposure to sun and wind, and I can see small leaves beginning to turn crisp at the edges. They were watered three times weekly on the deck, but now they’re in full wilt, requiring watering twice daily.

I’ve tried to fall back on the guidelines for container plants in stressful circumstances, clustering them together to form a microclimate (no effort required for that, as the path is already crowded), and frequently misting with a fine hose nozzle to temporarily cool foliage. I’ve also cut back stems to ease stress on root systems unable to adequately service limp leaves. I tried draping the containers with a white bed sheet to reflect light off their heated surfaces. These efforts are helpful, but haven’t solved the problem in any large way.

What has made a difference has been mulching the soil surface in each container. No matter if it’s a field of roses or a pot of begonias, covering the soil with organic mulch is the first and best defense against heat and drought. I was able to scrounge up enough leaves, pine needles and shredded bark to put a two- to three-inch (5- to 8-cm) layer of mulch around the stems in each pot, being sure to extend the materials all the way to the pot rims, and leaving no cracks where sunlight can enter. I learned that the depth of mulch is key to really keeping soil temperature cool, or at least cooler than it might be when fully exposed. A thin mulch (one inch / 2.5 cm or less) really didn’t do much, but the deeper layer resulted in cooler soil. As well, there is significantly less moisture evaporating, and watering has been cut down to once daily, delivered at night when plant tissues imbibe water and repair their cells.

It’s been a rough season for plants in containers, and there are still lessons to be learned about protecting them from excessive heat. I would also like the deck to finally dry, and for someone to spray the gardener with a hose.