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Garden Detective: planting Knockout roses

Rainbow Knockout rose (June 22, 2012)

Rainbow Knockout rose (June 22, 2012) Credit: Newsday / Jessica Damiano

DEAR JESSICA: I recently put up a fence running the length of my property, approximately 100 feet. It looks quite bare, so I was thinking of planting Knockout roses, which seem to bloom all summer and are very pretty. When is the best time to plant these, fall or spring? --Linda Deasy, via email

DEAR LINDA: Knockout roses are a wonderful idea. Now available in original (cherry red), Pink, Sunny (yellow), Blushing (soft pink), Rainbow (light pink with yellow centers) and double pink or red. All bloom repeatedly from June through frost and will provide greenery to soften the fence line even in winter. What's more, they resist mildew, black spot and pests and don't require any special care. You can plant them in fall through the end of October (you can get away with planting Sunday, but no later) or in spring. Be sure to observe recommended spacing guidelines, as they do grow large; one of mine has reached 6 feet tall and 6 feet wide.

DEAR JESSICA: With fall here and winter not far behind, is it safe and beneficial to put fireplace ashes in the vegetable garden? I only burn hardwoods. --Laura, via email

DEAR LAURA: If your soil is on the acidic side, which is the case throughout much of Long Island, incorporating wood ashes is fine as long as you're not growing acid-loving plants like rhododendrons, azaleas, blueberries, etc. Wood ashes not only will raise the pH of your soil (good for tomatoes, peppers, eggplants), but they'll also add nutrients like potassium, which can help improve the overall health of your plants, and phosphorus, which promotes a strong root system.

But be warned: If your soil already is alkaline -- with a pH of 7 or higher -- adding ashes could interfere with your plants' ability to thrive. And if it happens to be too acidic, you can't count on ashes alone to raise the pH substantially.

The only way to know what soil conditions you're dealing with is to test the pH level either with an at-home test kit, which you can find at local garden centers or online retailers, or by bringing a soil sample to your county's Cornell Cooperative Extension office (call 516-565-5265, extension 7 in Nassau; 631-727-4126 in Suffolk). Cornell will offer recommendations for improving your soil based on the test results.

Coal ashes and ashes from charcoal briquettes should never be incorporated into garden soil because they contain toxins.

DEAR READERS: Last month, I identified reader Tom Marren's tree as a wild plum, when in fact it's a trifoliate orange (Poncirus trifoliata). The tree bears a similarity to the wild plum in that it's very thorny and produces golf-ball-size fruit that starts out green. That's all I was able to ascertain from the early-season, close-up photo Marren sent, but as it turns out, if I had inspected the foliage more thoroughly, I would have realized the leaves are different. The orange has "trifoliate" leaves, which are compound leaves comprised of three leaflets apiece.

Many thanks to eagle-eyed readers Jennie Townsend of Center Island, Mario Facinelli of Northport, Vinnie Drzewucki of Freeport, Leo McSherry of Hempstead, Christopher Camastro of Springs, Joan Prior of Port Washington, Kenneth Hoffman, Case Joosse and Patricia Garry, who called me on this, giving me the opportunity to set the record straight. Facinelli sent a photo of his own trifoliate orange.

Now, a bit about Poncirus trifoliata: Also called "hardy orange," the trifoliate orange is a multibranched tree covered in super-sharp, 2- to 4-inch-long spines. White flowers cover the tree in spring and are followed by fruits that turn yellowish-orange in autumn and hang on after the leaves have fallen. The tree thrives best in full sun but can handle a bit of shade. The fruit is not harmful, but is considered inedible because it is extremely tart, although it can be used in highly sweetened jam. Trees also can be grown in a row and kept trimmed as a hedge; their vicious spines should discourage animals, trespassers and robbers.

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