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Gardening Q&A on Coleus, Mosquitoes and More

Master gardener Paul James discusses coleus, akebia, mosquitoes, trees in pots, cleome and more.

Master gardener Paul James answers questions on a variety of summer gardening topics.

Q: I love to grow sun-loving coleus. Where can I find seeds for some?

A: Sun-loving coleus types are cultivars, and according to the International Code of Nomenclature for Cultivated Plants, a cultivar must retain its distinguishing characteristics from one generation to the next. The only way to do that is to propagate the plants from cuttings to maintain their genetic purity and thereby retain their amazing leaf patterns.

It's easy to grow your own coleus from cuttings. Just take a section of the stem tip with at least three leaf nodes, strip off most of the lower leaves, stick the stem in a container filled with water and set it indoors in a sunny spot. In just a few weeks, it'll take root and be ready for planting.

Q: Why do you recommend akebia when it's known to be an invasive vine?

A: The truth is akebia can be invasive, particularly in the Pacific Northwest and on the East Coast, but in Oklahoma where I garden, it's rather well-behaved. That's the way it is with a number of plants. In some parts of the country, they may perform beautifully, while in other areas they may be anything from weedy to downright invasive.

If you're not sure whether or not a plant is invasive, do your research on how the plant grows in your area. Ask fellow gardeners or your local agricultural extension agent about their recommendations for the plant and for possible alternative plants.

Q: Why don't you focus more on native plants?

A: I grow a lot of native plants, including trees, shrubs and perennials, but I mix things up in my garden by also using non-natives. One of the problems I have with the "nothing if not native" movement is that it assumes the growing conditions in every neighborhood are indeed native. But very often, that's not the case. In new housing developments, for example, the native topsoil has often been removed and replaced with topsoil that's from somewhere else. And that results in a condition that's manmade, not native. As a result, many native plants have a tough time adapting to those conditions. Still, I urge gardeners to grow native plants whenever and wherever possible, largely because they're so well adapted to the climate in a given area.

Q: Double-digging is not the way to garden. It's too much work. What are your thoughts on the subject?

A: While I'd be the first to admit that double-digging requires a lot of effort, I disagree with your assessment that it's not the way to garden. After all, thousands of people, including myself, have been double-digging for decades, and the results are impressive. Moreover, it's a one-time-only process. After the initial digging, the soil can be left undisturbed virtually forever, provided the site is routinely topped with compost.

Q: How long does it take mosquito larvae to develop into adults?

A: It takes as few as four days for some species of mosquito larvae to develop into adults. The larvae can develop in a mere thimble full of water, which is why it's so important to routinely patrol your yard after a rain and dump anything that holds water, including wheelbarrows and pot saucers. Don't forget things like clogged gutters, holes in trees and even plastic wading pools.

But keep in mind that if the water is flowing, there's no need to worry. Mosquito larvae need still water to develop.

Q: Are there any natural alternatives to the insect repellents that contain DEET?

A: Do you have a problem with slathering N,N-diethyl-meta-toluamide all over your body? That's good, because in high concentrations, DEET, as it's more commonly known, may be hazardous. That's why it's best to apply the stuff to your clothing, rather than your skin.

According to the Centers for Disease Control, the most effective alternative to DEET is the oil from lemon eucalyptus, but even those formulations shouldn't be used on children under three years old. Other alternative products contain varying amounts of citronella, cedar, peppermint, lemongrass, clove oil and geraniol, which is extracted from geraniums.

Q: How hot should compost get?

A: Properly maintained, a compost pile of the proper size, which is at least three feet square at the base and three feet high, should reach an internal temperature of between 125 and 140 degrees F. In some cases, the pile may heat up to 160 degrees, which is hot enough to destroy weed seeds.

The best way to verify the temperature is with a special compost thermometer that features a long probe. Stab it into the center of the pile, wait a few seconds and note the temperature.

If it's not at least 120 degrees, then chances are you need to turn the pile to incorporate more oxygen into it or add moisture to facilitate the breakdown of organic matter. If you notice a sudden drop in temperature, that's nature's way of telling you the process of decomposition is complete, and the compost is ready to use.

Q: Can you grow cleome in USDA Zone 5?

A: Yes, you can grow cleome pretty much anywhere as an annual. It's worth growing for sure, not only because most varieties are quite beautiful in full flower, but also because the flowers are bee magnets.

Q: How long can you leave trees in containers?

A: That depends on the size of the container and the type of tree you're growing in it, but generally speaking, trees should be repotted about every three to five years, either just before bud break in late winter or early spring or in the fall. During the growing season, they should be watered often and fed every few weeks with a slow-release, organic fertilizer — ideally one that contains beneficial mycorrhizal fungi.

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