Ron Kujawski | Garden Journal: Functional boxwoods need a little TLC


"One of the most functional plants in garden history, it has been used for screens, hedges and foundations in the great gardens of the world."

These are the words of noted horticulturist Dr. Michael Dirr from his book, "Dirr's Encyclopedia of Trees and Shrubs" (Timber Press, 2011).

The "it" he refers to is boxwood, a functional plant even in my humble garden, where it stands as sentinel at the steps leading to our front door. Similarly, a matching pair of this bold evergreen shrub stands guard at the entrance to the front garden.

Yet, as stoic as these boxwoods seem, they are not without weakness. Examination of the undersides of their leaves now may reveal blister-like swellings. Scratching open a blister will expose tiny worm-like creatures. These are the larvae of the boxwood leaf miner. With warming weather, the larvae, which slumbered through winter within the boxwood leaves, have begun feeding between the upper and lower leaf surfaces. Heavily infested leaves will gradually become discolored and eventually drop, resulting in a ragged-looking plant.

Later this month, the larvae will transition to the adult stage, an orange-red fly resembling a mosquito. After mating, the flies will insert their eggs into the undersides of newly formed leaves of boxwood. While it is difficult to control leaf miners without resorting to pesticide application, home gardeners can achieve some success in reducing this pest population by a hard pruning of boxwood in early June. Fortunately, boxwoods can withstand a severe pruning and will soon produce new growth.

This information is not meant to discourage anyone from planting boxwood. It is still a very desirable shrub with many uses in the home landscape. Planting time is actually a good time to begin managing the leaf miner problem by selecting and planting varieties of boxwood that have shown resistance to leaf miner. Among the varieties with resistance are: Winter Green, Winter Gem, Fastigiata, Suffruticosa, and Varder Valley. I'm sure the folks at your local nursery and garden center can help with other suggestions for resistant varieties.


Here are some suggestions to enhance your gardening pleasure:

- Dig up the turfgrass around trees in your lawn and place a 3-inch layer of coarse wood chips or bark mulch over the bare soil. The mulched zone should extend at least a couple of feet from the tree trunk. This accomplishes several things. It keeps you from ramming the trees with your mower; reduces competition between tree and grass roots; helps maintain soil moisture; and over the long haul, contributes nutrients to support tree growth. Studies have shown that such mulched trees grow more vigorously than those surrounded by grass. Just one word of caution: do not pile mulch against the tree trunk.

- Keep an eye — maybe both eyes — on your rhubarb plant. Rhubarb is growing fast and there are probably a few leaf stalks ready to harvest. Pull off the stalks rather than cut them. Also, remove any flower stalks which appear at the center of the plant.

- Apply fish emulsion, dried blood, dehydrated cow manure or other high-nitrogen fertilizer to garlic, onion, shallot and leek plants. These members of the onion family require a high source of nitrogen during their early growing phase to promote ample leaf growth. With garlic, apply the fertilizer now; with onions and leeks, wait two weeks after setting out plants before applying the fertilizer; with shallots, apply fertilizer when shoots are 4- to 6-inches tall. Make additional applications to all at two-week intervals until mid-June. To produce the largest bulbs, these plants will also need frequent watering through the same period if rainfall is deficient.

- Sow seeds of Thai basil in a large flower pot. Thai basil has a licorice flavor and adds a little more zip than sweet basil when chopped and mixed into salad dressing. You might also try lemon and purple basil to expand your basil palate. All basils are easy to grow in the garden, but I prefer to grow them and many other annual herbs in pots since their foliage stays cleaner than when garden grown and the pots can be placed closer to the kitchen door than the herb garden.

- Be sure to sharpen the mower blade before heading out to the "south 40" to slay grass. A dull mower blade tends to tear the grass rather than cut it. With power mowers, always disconnect the spark plug wire before attempting to remove the mower blade.

- Cut back leggy house plants. Instead of discarding the cut off stems, try rooting them in a pot of most sand and peat moss. Rooted cuttings of geranium, impatiens and coleus can be planted outdoors in flower borders in early June.

- Leave their leaves intact after spring flowering bulbs have completed their floral display. They'll need these leaves to replenish the carbohydrates consumed in the flowering process. The leaves may be cut back after they have turned brown.

- Hmmm! When should snowdrops (Galanthus) be divided? This has become quite a controversial issue of late, especially in England, where snowdrops are one of the most adored spring flowering bulbs. Some British gardening authorities are adamant that they not be dug and divided until their leaves turn brown. Others are just as adamant that clumps of snowdrops be dug and divided just after flowering is complete and the foliage is green. What to do? I'll leave it up to you. I've had success with both methods. Maybe some folks just like to be argumentative.


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