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Gardening Q&A: Reseeding Plants and Bonsai

Master gardener Paul James answers viewer questions about controlling privet, repotting bonsai and more.

Q: Why is arugula growing like a weed in my garden?

A: Although ordinarily grown as an annual throughout much of North America, there are varieties of arugula that are perennial even in USDA Zone 5, and they reseed readily. For example, rustic arugula does indeed spread. The only way to prevent it from spreading is to pull the seedlings as they appear, or lift more mature plants out of the ground. However, if you love arugula, its tendency to spread is a good thing, especially when it's so flavorful, and you can enjoy its small, narrow leaves, cute yellow flowers and wonderful lemony, peppery taste.

Q: How do you get rid of wild privet and grapevine?

A: Privet is another plant that reseeds readily, and the only way to keep it under control is to pull it out, roots and all. Thankfully, that's pretty easy to do, even with large plants. Wild grapevines are another story: Their roots are more firmly attached in the ground, which makes them more difficult to pull. If you leave just a little piece of root behind, you'll soon have more vines. So, you'll either have to dig the roots out with a mattock or similar tool, or cut the main vine just above the ground and quickly apply horticultural vinegar or a thick paste made from water and table salt to the exposed tissue.

Master gardener Paul James answers viewer questions about controlling reseeding plants, winterizing water features, repotting bonsai and more.

Q: What is one interesting plant in your garden this year?

A: Bloodleaf (Iresine herbstii 'Blazin') is one of the newest plants in my garden. What I love about this plant – which, by the way, is a tropical and hardy only in USDA Zone 10 – is that it makes a great bedding plant for seasonal color. It prefers shade, especially in the South, and it grows best in moist soils, whether in the ground or in pots.

Q: Is Tricyrtis easy to grow?

A: Yes, Tricyrtis, better known as Japanese toad lily, is easy to grow. Most varieties are hardy to USDA Zone 5, and as long as you grow them in a rich, moist soil in the shade, they'll reward you with cool foliage and awesome flowers for many years to come. The bloom time for many Tricyrtis is late summer into fall, a time when few other plants flower, which is yet another reason for growing them.

Q: Is there such a thing as too many grass clippings in a compost pile?

A: Yes, at least initially. Fresh grass clippings are almost pure nitrogen, and unless they're mixed with a carbon-based material, or something brown, they'll give off an intense smell of ammonia. In time, of course, the grass clippings themselves will turn brown, indicating that the nitrogen levels have dropped significantly and leaving behind organic matter that's rich in carbon.

So, if grass clippings are the primary ingredient in your compost pile, make sure you turn your pile frequently, about once a week. As fall approaches, add shredded leaves or used potting mix to the pile to balance the carbon to nitrogen ratio.

Q: Are jalapeno peppers supposed to turn red?

A: All jalapenos start out green, and most are harvested while still green. But if left to mature, they'll turn red. At the red stage, they have a deeper, sweeter flavor. If you like to make your own chipotle chilies, which are nothing more than smoked jalapenos, red is definitely the way to go.

Q: Do water features have to be drained for the winter?

A: It depends on a number of factors, including the climate in your area, the depth of the water feature, and whether or not there's running water in the form of a waterfall, fountain, or bubbler. In all but the coldest regions of the U.S., large water features that include a pump through which the water circulates and are at least two- or three-feet deep can be left running throughout the winter.

The water may freeze up to a foot thick or more in some sections, but water that's agitated as it flows over a fall rock and the area below it aren't likely to freeze. In a koi pond, you might want to install a special pond heater to keep a small portion of the surface from freezing to prevent the buildup of gases that are toxic to fish.

Small water features, and those that include ceramic pottery, are a different story. They definitely should be drained completely to prevent freezing and cracking.

Q: Have you come across any new mulches lately?

A: As a matter of fact, I have. I got in the habit of collecting wine corks, for no reason other than each cork captures a memorable moment in time. One day I realized I could use the corks to mulch a few container plants, and I liked the look. Of course, it takes a while to collect enough corks to mulch a large-sized plant.

Q: How often should you repot bonsai?

A: The repotting timetable depends on the type of bonsai you're growing. Generally speaking, conifers should be repotted every three to five years and deciduous trees and tropicals every two to three years. The exception is fruit trees, which should be repotted every year or two.

Q: Can you harvest potential bonsai from the wild?

A: Yes, but before getting to that question, research the various sources for bonsai. Seeds and plants can be purchased from specialty catalogs or online sites, and nurseries often have plants that have bonsai potential. I bought all my conifers for bonsai either online or from local nurseries. Not all of them will make great bonsai, but many have the form and structure that bonsai enthusiasts look for.

Getting back to the question, it's fine to harvest potential bonsai plants from the wild if you have permission to do so. In fact, many bonsai specimens originally came from wild-harvested plants. However, many of them are hundreds of years old too, and the laws were different in those days. Today it's illegal to harvest plants on state or federal lands such as parks, so the only way to collect plants from the wild is to get permission from owners of private property.

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