Plants struggling with the heat

Judith Adam

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Ivy geranium Caliente Hot Coral (Photo by Brendan Zwelling)
Ivy geranium Caliente Hot Coral (Photo by Brendan Zwelling)
Ivy geranium Caliente Hot Coral (Photo by Brendan Zwelling)

It’s hot as Hades (again!), and I frequently need to remind myself that this is early July, not August. Plants are struggling to stand in the heat and wind — or perhaps I could say that I’m the one struggling to keep them going.

Strong sunlight has made beds by the front walkway inhospitable for plants like Durand’s clematis (Clematis x durandii, Zone 6) that bleaches to grey in midday sun, then returns to deep blue at night. Pink flowers on gold Magic Carpet spirea (Spiraea japonica ‘Walbuma’, Zone 4 ) open to burning sun and are finished in the same day. Three clumps of recently planted ‘September Charm’ Japanese anemones (Anemone x hybrida ‘September Charm’, Zone 5) are wilting and show crisping in leaf margins — they need deep watering daily. The dwarf tomatoes (‘Windowbox Roma’) in containers on the path also had bleached foliage, and had to be moved to part shade.

As for the water bearer, I’m on a tight irrigation schedule. Anything growing in a container (and why did I make so many?) requires watering twice daily. After a day of being buffeted by hot winds, plants have used up their moisture reserves in the containers and need replenishment. They get a big drink when the sun goes down, and by morning that water has been taken up and a second drink is required to give their roots something to pump upward when the call comes in the hot day ahead. This seems to be sufficient for some, like coleus and begonias, but not quite enough for others, like the morning glory and moonflower vines. Planted in containers, the vine heights are boosted 12 inches (30 cm) higher than they would be if grown in the ground, and that exposes their broad foliage to even more hot wind. Their leaves wilt in the sun and recover at night, but I notice that the lower leaves are beginning to fade and fall off, a trend that will probably work its way up the vines. Nevertheless, they’re growing vigorously at the top and I still hope for flowers.

Some plants have surprising resilience in extreme weather conditions. Two small concrete containers are filled with Caliente Hot Coral ivy geraniums (Pelargonium ‘Cante Hocora’). These are getting by with just daily watering and look terrific. They’re unphased by the heat and wind, and require only having their spent flowers removed twice weekly. Another high-performing plant in the heat is Supertunia Bordeaux, a self-cleaning petunia (no deadheading required) that makes a low six- to eight-inch (15- to 20-cm) mound and trails down 24 inches (60 cm). This is in the only container I haven’t needed to remove from the most exposed spot on the front walkway; it seems to love the heat and sun.

Besides watering, the next best thing I can do for plants is pinch and cut back some of their foliage. Removing excess green tissue that demands moisture replenishment will reduce stress on the roots. When the current hot spell is behind us, I’ll feed (using a ratio with a higher middle number like 15-30-15 to promote flower buds) to get these plants back on track for the rest of the summer.

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