The Garden Plot

Adrian Higgins
Washington Post Garden Editor
Tuesday, November 15, 2005 11:00 AM

Got a chronic case of green thumb? Like getting your hands dirty? Adrian Higgins , garden editor for The Post's Home section, is here to help. Higgins is a firm believer in "tough plants for tough times" -- the varieties that combine good looks with stiff resistance to disease and pests. He currently rules over a garden filled with spring bulbs, daffodils, ornamental onions, perennials, asters, yarrows, hostas and day lilies. Higgins, an avid organic gardener who believes chemicals are a last resort, also tends his own herb and vegetable gardens where he grows peas, garlic onions, lettuce, rhubarbs, radishes, carrots and more.

Higgins is the author of two books, "The Secret Gardens of Georgetown: Behind the Walls of Washington's Most Historic Neighborhood" and "The Washington Post Garden Book: The Ultimate Guide to Gardening in Greater Washington and the Mid-Atlantic Region."

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Dumfries, Va.: Some of my irises are blooming. Do I feel lucky, or sad for next year's blooms?

Adrian Higgins: Some iris varieties have a tendency to rebloom. Certain varieties, called rebloomers, have been selected expressly for fall show. Will this affect spring blooming? I would think it would. If you feel you don't have enough flowers in May, get some more irises.

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Madison, Wis.: Should Iris rhizomes be mulched ? I've read conflicting advice for my zone (4).

Adrian Higgins: Iris germanica are hardy down to Zone 3, which is even colder than Madison, I think. I don't know what the local practice is there. If you do lay a winter mulch, you should remove it in the spring, which in Madison occurs from May 27 to June 3, so that the rhizomes are kept dry to avoid rotting.

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Springfield, Va.: Earlier this year, I placed a weeping japanese maple (approx. 3' tall) in a large terra cotta pot. What is the best way for me to overwinter the tree? I know it needs to remain outdoors but am concerned about the pot cracking. Thanks for your help!!

Adrian Higgins: A terra cotta pot is not a good choice for a hardy tree, which must remain in its container for years. Even if the pot makes it through one winter, it won't the next. Also, unless the pot is at least 36 inches in diameter, you won't have enough room for the tree's roots. If you have to grow an acer in a container, I would invest in a nice wooden planter. Some are designed in the Japanese style expressly for acers. A tree in a pot will also need more diligent watering and feeding.

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Takoma Park, Md.: Hello, Adrian- I have a question: in the Real Estate section of the paper last weekend, someone asked about pruning hydrangeas. The recommendation was that the best time to prune was in June ("after blooming"). I don't get it-- my hydrangeas bloomed all summer and into fall. My understanding was that they should be pruned back hard in the fall and new growth will appear in the spring but the recommendation in the paper said that next year's blooms will appear on this year's growth. I'm very confused now.

Adrian Higgins: If you are confused, the best thing to do with a hydrangea is absolutely nothing. If you prune now, you will remove stems that will produce flowering buds next year. The only reason to prune or trim a hydrangeas is to remove canes that have died, and to reduce the thicket of growth that is produced after several years. The latter is best done after flowering so that you get a full floral show first. You remove no more than a quarter of the stems in one year. This will open up the plant, make it more attractive and promote better and larger blooms the next year. Hydrangeas typically bloom in June and July here, and the dried flowers remain ornamental through the fall.

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Potomac, Md.: Hello. Love your book and chats. I have a Japanese Maple, planted just this fall, that is suffering from white tips. I'd say about 1/4 of the branches have this problem. Should I trim off the white, or prune all the way down to the trunk? What is the cause of this?

Adrian Higgins: Japanese maples can get blackened stems from an unsightly fungus. I don't know about the white ones, could this just be the coloration of this year's growth? If the stems are living, you should not cut them back. This will disfigure one of the most beautiful plants in the garden, as well as promote a thicket of growth at the cuts. You can scrape the bark with your thumbnail, if it shows green beneath, the branches are still alive.

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Bowie, Md.: Hello Adrian,Enjoy the read every week and will miss it when you go into hybernation later this month. I have rabbits eating my plants and now they have started eating the flowers on my pansies. Short of putting mesh around everything, is there another way of controling those critters? Thanks for the advice.

Adrian Higgins: The only rabbit proofing, other than calling Wallace and Gromit, is to put netting around the garden, making sure it is submerged a bit to discourage digging.

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Leesburg, Va.: I have a lilac bush that has had severely malformed leaves The look is as though they were plastic and subjected to high heat - don't know if that makes sense, but they are not discolored, just malformed in some parts of the plant. The plant hasn't bloomed in two years. Can you hazard a guess as to what it might be?

Adrian Higgins: Severe infestations of powdery mildew will cause leaves to distort. If the leaves are gray-white and distorted, that's the problem. Otherwise it might be an insect called a leaf roller. I would prune out the older stems to promote air circulation and encourage better flowering.

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Burke, Va.: Which will do better in full sun - Nandina or Andromeda? Both are in semi-shade now and neither is thriving. But my only alternative is lots of sun. Thanks.

Adrian Higgins: Nandina by far. Pieris or andromeda will get severe lacebug infestations in full sun.

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Olney, Md.: Dearest Garden Guru: Thought the combination of cherry laurel and liriope would be unappealing to the deer. Newly planted liriope have been munched on so hard, two of them were yanked right out of the ground. Have sprayed Deer Off and waiting for results. What else can be done to protect new foundation plantings?

Adrian Higgins: I suppose you could net the new liriope until they have rooted over the winter.

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Linden, Va.: Adrian - I'm trying to prepare some asparagus beds this fall for planting next spring. I was thinking of tilling under my fallen leaves to add organic material to the soil. Is this a good idea? The leaves have been collected via lawnmower and most are chopped up, but some are nearly full size. My concern was regarding the decomposition of the large leaves.

Also, is there any problem with planting one the standard variety (green) next to the purple type of asparagus?

Thank you!

Adrian Higgins: Good soil amending and building is essential for a successful asparagus bed, as it full sunlight. This is an excellent time to ready a bed for spring planting. The leaves will be fine, but do try to chop them up before working them in, this will cause them to decay fully before planting. You can use pine straw, but it may increase the pH below the aspragus' desires, so also add some limestone when you do it. Purple and green together are fine. Male plants are considered better producers than female plants, though the berries are quite ornamental in the latter.

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Frederick, Md.: We'd like to plant a small tree in our back yard. There are no other trees in the area so it would get full sun. Ideally, we'd like to put a bench underneath the tree. Do you have any recommendations? We've looked at a river birch or dogwood, are there any other contenders? Also, is it too late to plant one this year?

Thank you

Adrian Higgins: You can plant a tree anytime the soil is workable in the winter. River birches can be difficult here, they detest drought. But if you can place one in soil with enough organic matter that it will retain moisture, it should be all right. Heritage is the classic Betula nigra for our latitude.

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Arlington, Va: Should I trim down my liriope for the winter? My brother in NC mows over his after the season, but mine are not in a place I can do that. Right now they have many many berries on them.

Adrian Higgins: I keep mine as long as they are looking ornamental, and then get the hedge shears to them in March before the new stems erupt.

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Frederick, Md.: Adrian, don't leave us for the winter! Now I am sad.

Adrian Higgins: I am flying south. To deepest Alexandria.

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Dunn Loring, Va.: Thanks for doing these chats. I finally have a question for you. We moved to a new house and recently planted a number of bulbs (irises and daffodils)in a bed and covered them with mulch. However, this space looks a little barren so I was thinking of planting hostas in the spring to provide a little more greenery. Would this disturb or otherwise hinder the bulbs from blooming? Would some other cover plant be better suited for this application? Thanks.

Adrian Higgins: First, irises don't like competition from other perennials. They are better given their own romper room or they will have a tantrum. Second, it is better to plant bulbs after you have planted perennials, so that you don't place a hosta, say, over daffodils. The two need some elbow room.

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Germantown, Md.: Hi, Higgins, Always enjoy your discussion. I planted a maple tree late October. I just wonder whether I should keep watering it during the winter when the tree is dormant. If the answer is yes, then how often should I water it and when should I do it? Thanks.

Adrian Higgins: Good question. It is getting dry again at a key moment. New trees don't need a lot of water, but they need some. Make sure your maple is set high enough that the roots won't sit in standing water. (Seems to be a lot of sitting and standing in this answer, like a religious service, I suppose. I would make a point of watering all my evergreen plants now before the ground freezes.

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Rockville, Md.: Thank you for holding these chats every week. I've learned so much. This weekend, I brought my hibiscus plants inside. Now that they're inside, I realized that my apartment may be too dark. Though I have a lot of windows, its situated that no direct sunlight comes in (and a large tree blocks any other light). I've positioned my house plants near lamps, and they've all thrived well. Can I use this technique for my outdoor plants? And does it have to be a certain type of light bulb? (ex: fluroscent light)

Adrian Higgins: They may not flourish in subdued light, but they should survive, which is the object with hibiscus. A lamp will help, it doesn't have to be fluorescent, it is more important that you keep the room humid to some extent. Keep the plant away from heat vents.

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Philadelphia, Pa.: Adrian, Now that fall has arrived, how soon should I put down some winterizer on my lawn? I did reseed part of the lawn during Sep/Oct, so is it too soon or should I wait a while longer. Also, I've heard that winter is the best time to prune evergreens. I have some juniper that could be trimmed, is Jan/Feb the best time? I appreciate your help. Thanks.

Adrian Higgins: You can apply winterizing fertilizer now but it should be slow release. With soil temperatures cool and the grass not in active top growth, you don't want to apply a heavy and transient feeding of nitrogen. A juniper is a conifer, it won't regenerate from being cut back hard. You can trim it a little now.

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Charlottesville, Va: Adrian, Thank you for your thoughtful and informed answers.

Re the potted weeping Japanese maple. I am in the process of removing a red maple that died because girdling roots choked the other roots. Could you comment on the proper method of transferring a potted tree to the earth to prevent girdling roots?

Adrian Higgins: Thanks, the long term health of a tree starts when you buy it. A girdling root looks like an innocuous little thread wrapped around the base of a baby trunk, but it will grow to strange the plant as it grows. You can either cut it off, taking care not to nick the trunk, or select a tree at the nursery that doesn't have one. If you feel when planting it that you can tease the root away without cutting it, then do so, but keep an eye on it.

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Potomac, Md.: Greetings. Over the weekend, I sowed an area of a garden bed (well-drained, full sun) with seeds of Ascelpias tuberosa (butterfly weed) because I had heard that these seeds could be sown in the fall. Any tips on maximizing the number of plants that make it to maturity (I also hear that this might take a few years) would be greatly appreciated.

Adrian Higgins: This is the native perennial milkweed. I suspect the seeds need winter cold to germinate in the spring. I would simply sow the ripened seeds now and look for seedlings in the spring. They can be transplanted or thinned then as needed.

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Vienna, Va.: We recently had a gigantic pine tree removed from our yard. The tree guys did a great job but a large area filled with shade-loving perennials has been trampled to oblivion. What are my chances that the plants will be back in the spring? I had epimedium, lungwort, sweet woodruff, stinking hellebore, and daylilies.

Adrian Higgins: Surprisingly, they may come back well. Two of those, hellebores and epimediums, flower in late winter, so you will get an idea soon of whether they survived. I'm not sure I would go to the trouble of lifting them and replanting. See what happens, you may be pleasantly surprised. I would make a point of top dressing the beds with compost, an inch or two, to restore some porosity to the soil.

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Leesburg, Va.: I had some really wonderful New Guinea impatiens this year which I am reluctant to see die. Would they survive if I brought some indoors?

Adrian Higgins: Please don't try to keep impatiens through the winter. At best, they will get too leggy, at worst they will become diseased. Better to start afresh each spring with professionally raised, virus free stock that is rearing to go.

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Frederick, Md.: My roses are still blooming... when should I cut them back? And to what extent.

Thank you!

Adrian Higgins: Roses should not be pruned until late winter. Pruning now will encourage regrowth at the worst moment as well as winter dieback. You can trim tall canes, but not by much.

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Anonymous: Hello Adrian. You have often said that you use your lawn mower to pick up leaves instead of raking. I just tried that today, and I have to say it did not work well. Do you have any tips?

Adrian Higgins: Start the motor first. Sorry, having fun at your expense. I have a mulching mower with two pairs of blades. I leave the bag on, this soon gets full and once it does, the mower won't pick up any more leaves. But it is a good way of assembling leaves for the compost pile while getting them off the lawn. You may want to lower the cutting height a little to see if that does a better job.

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Madison, Wis: My mother and I have a disagreement about whether I should plant a tree in the courtyard of my house next spring. I would like to plant a small (less than 15 feet tall) ornamental tree about four feet from the foundation and sidewalk, which my mother believes is a bad idea. She said that the roots will crack the sidewalk and ruin the foundation. Is she right?

Adrian Higgins: A small ornamental tree is unlikely to damage foundation masonry, but plant it with enough space for the roots and branches, i.e. at least six feet, at least, from the wall. After 40 or 50 years, it may crack surrounding paving, but so what? It won't bring down the house.

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Ellicott City, Md: I have a sick weeping willow tree. A portion of it lost leaves over the summer. This past weekend, I noticed that same portion has areas of foam - attracting a multitude of flies. What can I do to save the tree?

Adrian Higgins: Gotta know when to hold 'em, gotta know when to fold 'em. Foam, flies? Get that thing outta here!

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Ricmond, Va.: I am sorry your chats will come to an end for this season. It seems like I do more and more gradening "off season" ... particularly planning. You have mentioned trimming small trees after the leaves have fallen. Should I do that in late November or wait until late winter? Thanks so much.

Adrian Higgins: I like my trees to be fully dormant before pruning them. I would wait until after Christmas, especially in Richmond. My last regular chat is next Tuesday. Due to popular demand, I will be doing a a holiday chat on Dec. 6 at the regular hour where we can talk about amaryllis and poinsettias and greens and the like.

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Arlington, Va.: I am trying to learn the name of a shrub in my yard and how to take care of it. It has a about a dozen woody stems six feet high and produces six to eight inch cones of small purple/lavendar-colored flowers. Butterflys love it. I need to know whether I can prune it and if so, when, and any other care tips. Thank you.

Adrian Higgins: This is a butterfly bush or buddleia, named after a fellow named Buddle. Cut it back to about 18 inches in March and then trim back the new growth by about one third to one half in late May. This will encourage a bushier specimen. I think I hear my editor calling: Time to get back to work. Thanks so much one and all. Same time next week.

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