With Director of Horticulture Eric Kimbrel
When winter begins, we hope we are already well prepared for it. The speed at which the weather can change on the mountain is amazing, so as early as October we begin to prepare for cooler nighttime temperatures and the possibility of snow. In late fall the temperature on the mountain can be inverted. What does this mean? Temperature inversion or thermal inversion is a reversal of normal behavior, when a cold front causes a shallow layer of polar air to move to lower latitude with a layer of warm air on top. Today the air temperature at the bottom of the mountain was 27 degrees Fahrenheit, and the temperature at the top was 38 degrees Fahrenheit. We take advantage of these days to work outdoors.
That work includes preparation for Visitors Season, making everything ready for the spring show. We mulch the trails and rake them smooth, we make the beds immaculate, and we prune and top-dress the plants with aged manure as needed. We use composted cow manure, which supplies nutrients at a lighter rate than chemical fertilizer. It also contains calcium, which plants use to build their tissues. Even woody debris supplies calcium back to the soil, so we distribute wood chips back into our landscape this time of year. Our soils here are acidic — sometimes too acidic — so we add lime to beds where pH is too low.
At the same time, insects are hatching and disease pressure increases. We scout the landscape inspecting the plants for signs of damage and new infestations. Sometimes old infestation or damage can be confused for new infestation, leading to unnecessary treatment. We only treat a plant when a threshold has been crossed, meaning the natural predators cannot stay ahead or the plant can no longer defend itself from the disease. This reduces pesticide applications and saves beneficial insects, which make native plants so easy to care for with fewer problems.
When you do need to treat for insect pests, try to use a systemic insecticide applied to the ground and absorbed by the roots. That way you’re not spraying beneficial insects that may be hanging out on the plant, and only insects that chew on the plant will be affected.
This is a great time of year to look closely at your rhododendrons. Inspect for broken or dead branches, which is one way borers can enter the stem center where they lay their eggs. Look for holes burrowed into the end of the stem and cut that stem off at its origin. Throw away that infected branch to get rid of any eggs or larvae. Do not put it in the compost because it could live and mature to adult stage and lay more eggs. The best way to treat rhododendron for borers is again systemically through the roots.