Q: I have carnations and yellow alyssum that have become very woody underneath. The tops are good and flower well. Can I cut them back severely after flowering? Can I root the green tops? How?
With carnations, you have to deadhead the old blooms to keep them continuously flowering. Try cutting them back to a couple of centimetres above the ground and adding a new mix of soil and compost under the woody foliage to help it grow back properly. Be careful not to overwater carnations: they won’t flourish in damp soil and only need to be watered once a week, unless it’s overly dry. It is possible to root the green tops. They are best planted in the fall. Choose a stem that has non-yellowing leaves that are close together. Cut back about 10-12 cm (4-5 in.) just below a node (where a leaf meets the stem) and remove any dead leaves or blooms. Plant the cutting in sandy potting soil in indirect sunlight and place a clear plastic bag or glass jar over the cutting, opening occasionally to let the plant breathe. It should take about a month to root, You can root the cutting in a pot and plant it in your garden in the spring.
Yellow alyssum often have woody stems. You’ll want to cut them back by one-third after blooms fade. Usually, alyssum reseed themselves readily, so they should grow back next season. Keep them in sun and well-drained soil. If you’d like to root a cutting, remove the lower leaves and plant the cutting in a pot. Like carnations, try placing a clear plastic bag or glass jar over the cutting. Leave the plant in a shady location with moist soil. Remove the cover when the plant has rooted and move to the garden in the spring.