Question: My broom plant has grown very large and right now it is in bloom with purple/yellow flowers. Is there a correct time to prune and how much should I cut off?
Answer: Scotch broom (Cytisus scoparius) is not seen that much in this area, but it does make a statement. The most common cultivars are brilliant yellow and at a distance it looks rather like a forsythia that's two months late. It is planted all over Europe and is considered a weed in the Pacific Northwest (it produces zillions of seeds, which can remain viable for 25 years before germinating).
Pruning should be done soon after flowering. The important word there is "should." Post-bloom pruning eliminates seed production and, more important, rejuvenates the plant by stimulating growth. If left unpruned for a few years, the lower parts of broom stems will become unsightly bare wood that will neither bloom nor sprout when belatedly pruned. Broom is not considered a long-lived plant, and proper annual pruning should keep a specimen vigorous and perhaps extend its life.
When pruning, examine the plant. Just below the twigs that flowered there should be young growth that did not flower. Cut above the nonflowering portion, which will elongate over the summer and bloom the next year.
Q: I received a beautiful greenhouse azalea, from a florist, with no care instructions. I assume this is a houseplant. How do I take care of it and will it bloom again?
A: The assumption is safe, though it is conceivable the plant is hardy. For a tender azalea to prosper, it should be treated as if it is growing where it would do well outdoors. That means that it needs plenty of light and a "winter" of sorts.
First, it must be planted in an appropriate medium. Let's presume the florist (or wholesaler) has already taken care of that (but then again this is a florist that gives no instructions!), but if you wish to repot it (no telling what that florist's planter looks like), the best course would be to make a mixture of soilless commercial potting medium, finely shredded pine bark and perlite in a 2:1:1 or 3:1:1 ratio. The pine bark helps provide the appropriate level of acidity, and it and the perlite enhance drainage, which is essential for an azalea. Do not use potting medium with fertilizer already mixed in.
From May through September or October, put it outside, preferably in a spot that gets plenty of light but not direct midday sun. For winter, it would greatly appreciate an unheated enclosed porch, where the temperature stays above freezing. Flower buds (which are typically set in August) are more vulnerable than foliage, so if a wicked freeze might take porch temperatures more than 5 degrees below freezing, find another location, but avoid shocking changes in temperature (40 degree porch, 70 degree living room, for instance).
Bright summer light and adequate watering (remember: well-drained medium) will enhance the setting of flowers buds for the following spring. Fertilizer is probably unnecessary. If the leaves become chlorotic (yellow with green veins) give a dilute application of Miracid.
- Michael Martin Mills