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Garden Questions of the Week
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Timely Gardening Information Every week the customer service staff at Hole's post up the most commonly asked questions. |
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There are black, nut-like clusters on my mayday. What are they and how do I cure them?
The Science Behind it: Your tree has likely been stricken with a serious plant disease called black knot of cherry. At the fruiting stage, the disease seems to billow out of the branch or trunk. The only solution is to prune out the affected branches well below the knot. Be sure to seal the pruned branches in a plastic garbage bag and to clean your prun-ing tools between cuts with a bleach or ethyl alcohol solution to prevent spreading this disease. It affects all members of the genus Prunus—cherry, mayday, plum, etc.
How should I clean my pruners after trimming black knot or fireblight off my trees?
Practical Answer: Cleaning your pruners between cuts is a good all-around practice. Two products work well: bleach (sodium hypochlorite) and ethyl alcohol (ethanol). Dip the pruners in the solution after each cut to avoid spreading disease. The Science Behind it: Bleach eats into metal, so don’t leave your pruners in the bleach solution for any length of time. After the job is done, apply a lightweight oil to the blades to prevent rust damage. Use a ten-percent bleach solution (one part household bleach to nine parts water) or a seventy-percent ethanol solution.
How do I get rid of fireblight?
The Science Behind it: Fireblight is a highly infectious disease of several species of trees and shrubs. It is the most devastating bacterial disease of apple, mountain ash, and members of the genus Prunus. There are several precautions you can take against fireblight: • Plant fireblight-resistant varieties. Some apple varieties are much more resistant than others. • Avoid pruning trees when the fireblight bacteria are abundant (i.e., spring and summer). • Inspect plants weekly and remove visible lesions or infected branches. Prune down at least 20 cm, then destroy the infected branches. Do not leave them in your yard or attempt to chip them and use them for mulch. • Disinfect pruning tools with bleach or ethanol between cuts to prevent spreading the disease.
I’ve heard about a blight that affects apple trees, and I’m a little worried. Can you tell me more?
Practical Answer: You’re thinking of fireblight. Keeping fireblight at bay requires constant vigilance. The Science Behind it: Fireblight is caused by a bacteria called Cerwinia caratovora. Caratovora is Latin for “starch eater.” It’s a good name, since fireblight breaks down the starches in tree shoots, flowers, and leaves. Some apples are more resistant to fireblight than others; check with your local nursery for the most resistant varieties. Avoid excessive application of high-nitrogen fertilizers that cause soft, leafy growth, which is more prone to fireblight attack. Pruning as soon as a branch becomes infected is your best control strategy; prune at least 15 cm below the visibly affected area.
My willow branches are turning black. They start to leaf out, then they shrivel and turn black. Why?
The Science Behind it: This sounds like a leaf blight caused by bacteria or fungi. Diseases are more of a problem during rainy spells. Fortunately, these types of blights usually don’t pose any long-term threat. Don’t bother spraying; just let the disease run its course. We commonly see these blights on dogwoods as well.
My cedars are turning black on the bottom branches. What’s the problem?
Practical Answer: Dog urine is the most likely culprit. Dog urine contains high levels of salt, which can burn foliage, turning it black. If possible, wash down the affected area immediately after the dog urinates. Then do your best to keep the dog away from the tree in the future. You may have to put up a barrier. The Science Behind it: We once had a customer who swore that window-washing spray caused the same blackening on the top of his cedar. Both urine and many cleaning solutions contain ammonia, so that may be possible.
My trees are budding too early. What do I do?
Practical Answer: This is a common question, and unfortunately there’s not much you can do. Humans simply can’t control the weather. Most established trees, even if they sustain some damage from fluctuating temperatures, will recover on their own. The best you can do is keep your trees healthy and disease-free so they have a better chance of surviving whatever Mother Nature throws at them. The Science Behind it: The arrival of warmer weather signals trees and shrubs to end their winter dormancy and begin sending out flower and leaf buds. The warmer the weather, the quicker the emergence. Once the buds begin to swell, they can be injured by a sudden drop in tem-perature. You can partially screen smaller shrubs from wind and sunlight, keeping them cooler and slowing the emergence of buds. Larger trees and shrubs, however, must fend for themselves.
What should I do to my shrub beds in the spring?
Practical Answer: Inspect the shrubs for winter damage, particularly damage by rodents. Prune out any damaged branches. Clean up any twigs, leaves, or other debris from around the base of the shrubs to re-duce pest problems and make weeding easier. Cultivate or loosen the soil, being careful not to damage shallow-rooting shrubs such as azaleas, rhododendrons, and daphne. Top dress the base of plants (but not up against them) with compost. Fertilize early in the season, while the roots are actively growing. These steps will get your shrubs off to a strong, healthy start.
In general, when should I prune my trees?
Practical Answer: Pruning is a general term that we use to describe everything from deadheading to removing large limbs. It’s best to prune large branches late in the dormant season. Prune in the late winter, just before spring growth starts. Of course, if a branch is broken or hazardous, it should be removed promptly, regardless of the time of year. The Science Behind it: Pruning in the summer, or while the tree is actively growing, can lead to several problems: • Exposed cut ends are more vulnerable to disease and insect in-jury. • If you remove too many leaves, you’ll reduce your tree’s ability to generate energy. • It’s harder to visualize the ultimate shape of your tree with leaves obscuring the view. • In some regions, it is illegal to prune trees in the spring or sum-mer due to insect problems. There are, of course, exceptions to the rule. We recommend that birch and maple be pruned in late spring or early summer when they are fully leafed out, and most evergreens are best pruned in late spring, while the new growth is still soft.
How do I prune clematis?
Practical Answer: With alpine, big petal, or yellow bell clematis vines, prune off only dead or broken branches. The Science Behind it: Many people cut back viticella and hybrid clematis vines in the fall, to 15-30 cm above soil level. Instead, protect the plants over the winter and prune them in the spring. To do this, gently remove the vines from their supports in late fall, and lay them stretched out on the ground. A few weeks before the soil freezes, water the roots heavily. Once the ground begins to freeze, cover the vines with 15-25 cm of dry peat moss. Uncover the vines in the spring and cut them back to the uppermost new growth.
When do I fertilize spring-flowering bulbs?
Practical Answer: The first time to fertilize spring-flowering bulbs is at planting time, in the fall. Even though you don’t see any above-ground activity, under the soil the bulbs are busily establishing roots to take up moisture and nutrients before they go dormant for the winter. Most bulbs also prefer a high-nitrogen feed (indicated by the first number on the fertilizer container) once during the growing season. Fertilize again after the bulbs have finished blooming in the spring. A general plan is to fertilize long-term, perennial bulb plantings at the end of the dormant season, just before growth commences, and again after flowering.
Should I fertilize fall-flowering bulbs in the fall or in the spring?
Practical Answer: Two principles come into play here: demand and convenience. Fertilizing at planting is easiest, but bulbs demand fertilizer most during the spring and summer. So why not do both? Fertilize bulbs like autumn-flowering crocus and colchicum when you plant (in the fall) and again the following spring or summer when the foliage is growing actively. This plan provides nutrients as the bulbs burst into bloom and develop roots, and again after dormancy when the bulbs are gathering energy to rebloom the following fall.
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