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Q&A ON MOST-ASKED SPRING GARDENING TOPICS
Q. I've been told that black plastic can be used to control weeds in gardens. How does it work?
A: Black plastic is used by some commercial gardeners as a mulch between rows of tomatoes, peppers and vine crops. The black plastic prevents weeds from growing between the rows. You can use garbage bags or special rolls sold at garden centers. Heavier plastic can be reused.
Q: The leaves on my birch tree are being eaten by something. What should I do?
A: The culprit is most likely birch leafminers. This insect overwinters as pupae in the soil. In the spring, adults hatch and fly to the birch trees. Eggs are inserted singly into the expanding leaves. The larvae hatch soon afterwards and feed on the plant tissue between the leaf surfaces, creating mines. Eventually, these leaves turn brown.
Healthy birch trees can generally tolerate leafminer infestations than damage less than half the total leaf area of a tree. Treatment, therefore, is necessary to protect a tree's appearance. Chemical sprays are most effective when leafminer larvae are first forming mines.
Q: In past years, green worms have attacked my spruce trees. Will they be a problem this year?
A: The green worms are most likely sawfly larvae. These 1-inch long green larvae love to devour the new candles on Colorado blue spruce and some other spruce species. Last year, they left my blue spruce alone but did quite a bit of damage to several white spruce on my lot.
The object of control is to stop defoliation before it becomes too extensive. That means you should check spruce trees every day or every couple of days until mid-June. For control of just a few trees, spray the larvae using a ready-to-use chemical approved for sawfly. Most garden centers sell these products.
Q: What affect will all rain in May have on container plants?
A: Constant rain can force the nutrients in container soil to drip out through drain holes, leaving a shortage of nutrients in the soil when dryer weather returns. I generally fertilize my container plants at least once a week when I water them. I mix a soluble fertilizer in each sprinkling can of water according to label directions and it seems to promote good growth. Most container plants need some additional nutrition during the growing season.
Q: I was thinking of building a raised garden using railroad ties. Is this a good idea?
A: Railroad ties aren't a good building material for raised gardens because they are messy and the wood preservatives used in railroad ties can be a health hazard. Creosote- and penta-treated timbers should not be used around plants.
Studies of landscape timbers treated with chromated copper arsonate have not
shown leaching to be a problem, at least in timbers that are not so old they are beginning to deteriorate. These timbers have been pressure-treated, and the chemical is bound tightly into the wood.
When purchasing CCA-treated timbers for the garden, choose boards that are
dry and have no moist or "salty" looking deposits on them, advises Deb Brown, University of Minnesota extension horticulturist. "Foundation grade" CCA timbers cost more, but have had an additional heat treatment -- a bit of extra "insurance," according to Brown.
If you don't want to use treated timbers, choose redwood or cedar. They are more costly than CCA-treated pine, and they don't last as long, but they are longer lasting than other untreated wood. You should also consider the interlocking landscape blocks that are made specifically for edging and retaining walls.
Q: When is it too late to plant a garden? I haven't been able to get in my garden because it's been so wet.
A: It's getting a little late for cool-season crops such as lettuce, broccoli, spinach and radishes. Many plants such as tomatoes, peppers and vine crops seem to prefer later planting (late May, early June). I've never done a comparison but I suspect pumpkins, squash, peppers and tomatoes that are planted in early June might mature just as fast as plants placed in cold, wet ground in early May. And annual flowers, of course, can be planted most anytime in early summer. Some annuals begin looking rather spent by late July and August and later planting can provide more colorful flowers into the fall season.
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PUTTING DOWN ROOTS:
A Delightful Blend of
Gardening Wisdom, Wit
and Whimsy
$10 + $2 for shipping
by Cliff Johnson |
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