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Answering your fall gardening queries

By Joel M. Lerner,

Autumn is the time of year when I probably get the most gardening questions from readers — especially when drought and heat have set records throughout the entire summer. Here’s my take on a few recent queries:

Q. I’ve raised and propagated African violets since high school: rooted leaves in water, potting soil, vermiculite and combinations of these ingredients. I thought I could use the same techniques for miniature African violets but nothing has worked. The leaves either rot or do nothing. What’s the deal?

A. African violets are finicky about temperature, light and drainage. Propagating them is a matter of timing. Try spring when you have bright, even light and temperatures in the range of 70 to 75 degrees Fahrenheit. Moist, well-drained conditions are best for rooting cut leaves. Miniature African violets should root the same as full size leaves.

The leaf requires at least a quarter-inch stem, which is what goes into the planting medium. The leaf surface should not lie against the potting soil surface. I also recommend dipping the leaf stem in a rooting hormone, like Root Tone, to encourage rooting. Miniatures will be slower to root and have smaller leaves.

Sterilize cutting tools with bleach before working with them. When you’re done, squirt a little light oil on the pruning tool — bleach is corrosive to metal. Botrytis causes the rot the leaves are susceptible to. You might require a fungicide like binomial to stem the problem. Follow labeled instructions.

Q. We’d like to obtain some privacy from our neighbor. What do you suggest that is fast growing and will provide some privacy that we can plant now?

A. Hedges are the most commonly used type of screening. If you want privacy without hedging, plant large conifers, like spruces and pines, in strategic positions to screen the view. There are also semi-evergreen and deciduous shrubs that are faster growing than conifers. Examples of good evergreen and semi-evergreen shrubs are Allegheny viburnums and chindo viburnums (V. awabuki‘Chindo’). Allegheny viburnums will grow about 10 feet high and wide in about 10 to 12 years and are semi-evergreen in winter. Chindos are fully evergreen and will grow about 15 to 20 feet high and eight to 10 feet wide in about 10 to 12 years.

Conifers should be planted in sun and well-drained soil. Allegheny and chindo viburnums are shade tolerant and will also grow well in sun with an eastern exposure. Plant viburnums about eight to 10 feet apart and install conifers on approximately 15 to 20 foot centers.

A lower growing, fully evergreen shrub for good hedging that will grow about eight feet high and wide is schip laurel (Prunus laurocerasus ‘Schipkaensis’). Plant where it’s protected from winter wind. Schip laurels and viburnums can be sheared or selectively pruned to maintain the size you want. Conifers should not be pruned. Plant these where they will have room to grow into full-size trees.

Q. I would like to know where to purchase a jujube plant or fruit.

A. The only place I have seen it available is by mail-order from the company Edible Landscaping (www.ediblelandscaping.com) in Afton, Va. Call them at 800-524-4156 and request a catalogue. They also offer other unique edible plants.

Q. Any idea why my green bean plant isn’t producing beans? I started it from seeds in the spring and have gorgeous plants that flower but never produce. I’ve been watering it consistently through the drought, but all it’s done is produce more flowers. The plant is in a giant pot and I used Miracle-Gro soil.

A. There are a few reasons that green beans won’t produce beans. According to well-known bean agronomist Nathan Peck, the cotyledons (seed leaves) will crack off the plant or the embryo breaks off and doesn’t develop. With the number of flowers you say you have, that sounds like a feasible explanation.

Here are a few other possibilities: You might have a lack of pollinators such as bees and butterflies. You can pollinate the flowers with a soft painter’s brush, taking pollen from one flower and lightly spreading it to others. Green beans need full sun — at least seven hours — and deep, compost-rich soil for their roots to spread.

Next year, prepare the soil by digging it deeply (about 12 inches) in March. Add one part each of compost to native soil that is somewhat alkaline (pH should be between 6.5 and 7). Most soil in this region is more acidic (between 5 and 6), so you might want to add about four to eight ounces per cubic foot of pulverized horticultural limestone to your planting area.

Bush beans grow better in containers with moist, well-drained soil and have added interest for children because they have to search through the bush to find the green beans.

Q. My yoshino cherry tree needs pruning. It is the focal point of our block when it’s blooming but now it is too large. When is the best time to prune and to what point on the branch do we prune? I suspect I will need a professional tree trimmer, as the tree is too tall for us to reach. Please provide your suggestions.

A. The most important question you asked is “to what point on the branch do we prune?” Most limbs on trees have a widened area at the base of the branch called the branch collar. Always cut to a crossing branch just above this point, which is the widened area where a tree branch grows from a larger limb below it. Your yoshino cherry should be pruned just as the flowers fade in spring. Do not prune now or you’ll sacrifice flowers next spring.

When pruning, pay careful attention to symmetry. Never top a tree or leave branch stubs. Elevate limbs that are low, eliminating danger of walking into them. Prune suckers that are growing up through the tree from its limbs and appear to look like sticks. Prune crossing branches rubbing against the bark of other limbs and cut off branches that create sharp crotches that could split from the tree in heavy wind or under heavy snow or ice loads. Assess other branches in the canopy of the tree that should be cut to clean out excess fullness and provide a balanced appearance.

Joel M. Lerner is president of Environmental Design in Capitol View Park, Md.

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