Summer is upon us. The freezing nights of spring are over, and days are warm in the sun. Now my plants and I are facing a different threat: the sun itself.
As a shade gardener, I’m always focused on sunlight. Light is a plant’s basic requirement, and in my tree- and building-shaded space, sunshine is hard to find. Yet too much sunlight, hitting a plant that isn’t built for it or isn’t ready for it, can also do harm, burning and crisping leaves and drying out blooms.
It’s important to be aware of the sun all through the growing season. As the sun’s position in the sky changes during the year, it shifts how light falls in any yard. Some areas, and some plants, may get too much light during one part of the season and not enough light at another time.
In my garden, May and June are the times of greatest peril from the sun. The leaves of shrubs and perennials are new, thin and vulnerable. Houseplants, most of them native to the understory of tropical forests where full sun never shines, are just moving outdoors. The trees overhead often don’t fully leaf out until late May. The days are growing relentlessly longer, increasing the overall amount of sunlight that enters the yard each day.
If mine were a sunny yard, the long, bright days would be good news, because I would have chosen plants that thrive in sun. But for most of the growing season, my space is a place of shade. My plants were selected for their ability to get by on the limited amount of light they will get in July, August and September. Hostas, brunnera, Solomon’s seal, ferns, begonias, bleeding heart, Celandine poppies, columbine, corydalis, Canadian wild ginger—they do well on just three to four hours of filtered sun a day, but they are not adapted to cope with direct, piercing morning or afternoon sun.
There are only a few ways a gardener can help: Keep the soil moist, so plants have access to the water they need to fill their leaves and cool themselves. Plant each species of perennial and shrub in a place where it will get the right amount of light in the long term. Some gardeners have a pergola or a shade structure over tender young plants or a shade-cloth-covered conservatory for shelter. But for my most vulnerable plants—my tropical houseplants—my solution is to keep ’em moving.
I spend most of May and June lugging potted houseplants around to find spots where they won’t fry. Some need to go under a shrub for a while; others will be okay on the north side of a wall. I often miscalculate. Since I’m not an early riser, I tend to underestimate the intensity of the shafts of morning light that reach between the buildings and tree branches. On the other hand, I often am slow to notice that another spot has become much shadier now that the tree overhead has fully spread its leaves. And of course, the sun hits slightly differently every day of the year.
Not all plants need the same amount of light, or protection. Any plant with variegated leaves—streak or splotched with white or any other color—is at a disadvantage compared to a plan green plant. The non-green areas have no chlorophyll, the green pigment that is essential for a plant to turn sunlight into food. To make up for that lack, a variegated plant may need a spot where it will get a little more light.
The same is true of plants whose leaves are yellow-green or red-green rather than plain green. They are also a little shy of chlorophyll, or, in red or burgundy plants, the green pigment may be screened by the red. A chartreuse plant in too much shade may lose its chartreuse, becoming a more ordinary green as it produces more chlorophyll to try to make enough food from not enough light.
Spring is the time I worry about too much sunlight. The rest of the year, I bend all my efforts to find more. My rose patch is awkwardly situated at the corner of the building, the only place where, because of a gap between trees, roses can get almost enough western sun (at least in June when the days are longest).
I will need to keep up my houseplant dance for a few more weeks. I’ll keep snipping off leaves with sunburned patches or crispy edges (a damaged leaf can’t heal; all a plant can do is grow a new leaf). Once midsummer arrives and the days start growing shorter, the light will gradually become less intense. Then I’ll go back to searching for light and not guarding against it.