Harsh Exposure Can Burn Foliage


UNITED STATES—Even though the weather can get uncomfortably warm at times through summer or a bit cool and damp in winter, this is still the best climate in the world. It does not get as warm for as long as warmer regions or Arizona do. Nor does it get nearly as cold as even the mildest climates of Alaska. Furthermore, minimal humidity makes the warm and cool weather more tolerable, at least for us.

Ironically, it is the minimal humidity that can actually make warm weather more uncomfortable for plants that should otherwise enjoy warmth in the garden. Gardenias prefer warmth, but also crave humidity. The foliage simply is not as happy with dry warmth. Japanese maple foliage likewise does not mind warmth, but can get roasted by drying breezes or direct sunlight during warm weather.

There are of course many plants that should not be too exposed to direct sunlight during warm and dry weather. Many ferns, azaleas, rhododendrons and philodendrons are naturally understory plants that prefer to be in the partial shade of larger trees. They should obviously be confined to sheltered spots.

Yet, even cacti, aloes and agaves can get damaged by severe exposure. They are not likely to get desiccated like thin foliage does, but can get roasted from sun exposure. Actually, the ‘hair’ that adorns old man cactus is actually for a bit of protection from harsh desert sun exposure.

Potted plants that have spent some time in sheltered or partially shaded situations are particularly susceptible to damage if suddenly moved into harsh exposure. They simply can not adapt fast enough. If possible, it is best to delay such relocation until late winter. This gives the plants some time through spring to develop foliage and stems that are adapted to the new exposure.

Plants purchased in nurseries are generally adapted to situations that they will likely be planted into. However, they may not be adapted to situations where exposure is enhanced by reflective surfaces like large windows, lightly colored walls, and pavement. Enhanced exposure makes the environment somewhat warmer and more arid, and can scald foliage.

Although scald is something to be aware of this time of year, most minor foliar scald of resilient plants is fortunately superficial. Damaged foliage will eventually be replaced with more resilient foliage. As plants mature, they absorb more ambient glare, so become less susceptible to subsequent scald.

Highlight: Saint John’s Wort

Warm weather has accelerated the bloom of Saint John’s wort, Hypericum X moserianum, which normally waits another month or so. Now that bloom has started, it should last through September. The bright yellow flowers are about an inch and a half wide, with prominent stamens and five petals. Mature plants get about two and a half feet tall, and are usually a bit broader than tall.

Resilient and undemanding Saint John’s wort is not too discriminating about soil, water or sun exposure. Once established, it prefers to be watered somewhat regularly, but can survive with minimal irrigation. Full sun promotes abundant bloom, but partial shade is not a problem. Plants that get cut back severely at the end of winter or beginning of spring perform better than plants that merely get shorn or pruned lightly.

By Tony Tomeo