The Garden Plot

Adrian Higgins
Washington Post Garden Editor
Tuesday, April 18, 2006; 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.

Catch up on Catch up onprevious transcripts of The Garden Plot.

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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Laurel, Md: I have 2 blueberry bushes that require relocation. They are budding now and they are three years old and three feet tall. What is the root structure going to look like? Do their roots grow out or down deep? Should I leave them alone?

Adrian Higgins: Blueberry bushes have a shallow, fibrous root system (which makes them prone to drying out and drought stress) so they are quite easy to move. Make sure your new site is sunny and the soil is well amended with organic matter. Consider working in some rotted oak leaves and pine straw to help acidify the ground. A three year old bush would probably need a root ball at least 18 inches across. It would have been better to have moved them in the fall, but I think they're young enough to transplant safely if you keep their soil moisture monitored this summer.

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Arlington, Va: When would be the best time to transplant Lilac bushes? The county is going to install a sidewalk along my corner lot this summer & in the process we will lose a 30 by 4 foot row of Lilacs unless we can move some of them. They range in size from one foot to 9 feet tall and have been there for about 40 years. I'm guessing the big ones won't survive the move.

Adrian Higgins: Lilacs are notoriously difficult to move. I would use the opportunity to pick fresher varieties better suited to our climate, such as Miss Kim.

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Lewes, Del.: Good morning ..I am building 6 raised beds to grow cutting flowers and vegetables. I am using pressure treated lumber for the frames as recommended by several garden books. My question is: Since arsenic is used in the treatment process for this lumber would it be safe to ingest food that is grown within the bed which is approximately 12feet by 4 feet in size. Thank you very much for any insight you or others may share.

Adrian Higgins: There are two schools of thought. One is that you should not grow edible plants in the vicinity of pressure treated wood. The other is that the chromium arsenate is very stable and doesn't transfer to the soil. Personally, I wouldn't want to take the risk.

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Washington, DC: While hunting for a book to start a garden in my yard basically from scratch, I came across "Square Foot Gardening". I remembered watching the PBS show in my youth in the 80s and so I bought it. I like the concept of the economy of planting by the square foot for my small yard and of building raised beds and filling them with a mix of light, airy soil. Any pitfalls I should be aware of before I embark on this project?

Adrian Higgins: I remember seeing that in the 80s in my infancy. Just kidding. It's a bit of a gimmick but the underlying principle of intensive cultivation is quite sound. YOu will find that however muchspace you give vegetables, they will determine how much they need. By far the best way to grow a lot in a little space is to build trellising and to grow things up, not out. Call it the Manhattan project.

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Arlington, Va.: Good morning, Professor! I'd like to ask your advice about compost please. I have a pile that I started last fall and it doesn't seem to be, well, composting. It's basically still just a pile of shredded leaves and other garden and kitchen detritus. I think part of the problem is probably lack of moisture due to the nonexistent rainfall over the winter, and part is my own lack of knowledge about how to compost. Is there anything I can do or something I can add to the pile to jump-start it into activity? Thanks for your help!

Adrian Higgins: Common problem in dry weather. I would rake it all out, shred it again with the mower, add some grass clippings and put it back, and then remember to water the pile thoroughly once a week.

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Washington, DC: Hello Adrian-- So, I think I've read on this chat that tulips these days are bred to give only one really good season of blooms. However, all instructions that came with the dirt-cheap Home Depot tulip bulbs I bought last fall--and that look spectacular right now--say to let the foliage die back before I chop it away, to promote future blooms.

Seems to me if they probably aren't going to bloom anyway next year, I can just rip 'em out the second the petals drop off, and put something else there. But they do look great, and I'll wait until the leaves die if there's a solid chance they'll come back next year. What do you think? Thanks.

Adrian Higgins: I'm talking about this in this week's Home section, but if you really want to try, cut off the flower heads after the petals drop, fertilize the tulips and keep them watered until they fade in early June. Then lift the bulbs, dry them in the sun for a day, and preserve them in a mesh bag in a dry, cool area over the summer. Plant them afresh in October. You may find you have a large bulb in June and a small one, the smaller will take two or three years to bloom.

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Reston, Va: My wife and I live on the top floor of an apartment building, and have a patio area with plenty of sunlight. We would like to grow veggies on our patio, but would be grateful for any recommendation you can provide on a soil mixture. At the moment, we have mixed dirt with used coffee grounds but am thinking that we should add Miracle Grow or something else. Thank you.

Adrian Higgins: I would make a mix of two parts peat moss to one part composted humus and one part top soil. Add liberal amounts of perlite for soil lightening and moisture retention. You could add the coffee grounds to the mix if you wish. Go easy on the Miracle Gro.

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Potomac, Md: Greetings. Heeding an article that you wrote last year in which you recommended sowing certain kinds of flower seeds in the fall, I sowed poppy, love-in-the-mist, and larkspur in a garden bed last fall. The love-in-the-mist germinated and is doing well, but I don't see much of anything else. Should I wait a little longer, or call the seed company (for a refund or more seeds) now?

Adrian Higgins: Certainly the larkspur foliage should be showing now, along with the rosettes of poppy foliage. It is important that the seeds be sown not on mulch or hard clay, but in a bed with very friable topsoil. It is possible that the seeds were washed away before germinating or blown off during leaf clearing in the fall.

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Mount Vernon, Va: Adrian - I'd love some advice for shrubs for the front of my house. It's a shaded area facing north which is very dry. I have some well established boxwood planted there, but in the last 5 years I lost both of the dwarf pine trees on either side of the door (I think both were lost to lack of water). I'd like to put something in their place and also replace a couple ailing azaleas that are barely hanging on. I'm thinking of more boxwood for the corners (where the azaleas are), but I was wondering if new plants would look good with established ones? Also, do you have any suggestions for the area around the door?

Thanks!

Adrian Higgins: Dry shade is tough for shrubs. I would consider Kerria japonica, aucuba and perhaps some mahonia.

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Silver Spring, Md: Recently I have seen some commercials talking about using Maryland recycled tires as mulch in your garden. Is this a safe product to use or should I be concerned about chemicals and what not leaching into the soil - particularly around veggies. Thanks!

Adrian Higgins: It is a virtue to recycle rubber, but not as a mulch, in my view. Mulch is used, in part, to cool the soil and build the soil, and rubber mulch can do neither. I can only imagine the soil temperatures generated by dark rubber in July.

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Squash on a trellis?: Professor, what kind of trellis do you suggest if I want to get my squash and zucchini off the ground? I have a small plot in a community garden and if I can free up some real estate by using a trellis, I'd like to do so. Thanks!

Adrian Higgins: What I do is take two by two cedar stakes, eight feet tall, and knock them into the ground about 18 inches. You will need a step ladder and a stone mason's hammer. They are positioned about three feet apart and then joined at the top, to form a narrow triangle. Truss them together. Repeat at the other end of the row. Then run a long pole between them. I then take nylon, not plastic, bird netting and lay one down as a sheet on one side, stapling it, and then do the other side. This presents a lot of growing areas for everying from beans to melons.

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last frost date: I noticed in your garden book that the frost free date varies wildly in this region (National Airport Mar. 30 and Arboretum May 1!!!). In Arlington, when can I safely assume it's okay to plant zinnia, cosmos, and marigold seeds? Thanks.

Adrian Higgins: This is a very good question. Perhaps due to global warming, but last frost dates have been moving steadly earlier over the past 20 years, in my experience. I need to check, but I think my last frost in Alexandria was in mid-March (it comes just as the magnolia blooms, nature's kick in the pants). I don't anticipate any more this season.

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Linden, Va: I planted spinach seeds last fall, but I don't have any plants yet. Are they still on the way, or has the drought ruined them? I watered them weekely for the last few weeks, but not at all in Jan and Feb. Am I just impatient?

Adrian Higgins: No, the object of fall sowing is to have germination before winter and a rapid regrowth in the spring. Spinach needs even moisture to germinate and grow and if you relied on rainfall for this, I think you were out of luck. You could sow again for a harvest of baby spinach in early June, and then hold off until early fall.

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First Time Gardener: This may be a silly question but as a new homeowner and a newcomer to the gardening/landscaping world, I hope you can help. We have a tree with large roots smack dab in the middle of a brick patio with little landscaping surrounding it. We'd like to simply mulch the area and possibly add a ground covering, but I'm uncertain what the first steps to take are. Do we use soil to cover the intending mulching/planting area first?

Thanks!

Adrian Higgins: If you simply want to tidy the area, you can place a THIN layer of mulch on or between the roots, depending how proud they are of the ground. I wouldn't attempt to grow anything under the tree, this will be a disappointment and if the tree is of an inferior species, say Norway maple, you may want to remove it. The practice of placing mulch in a mound against the trunk or bole of a tree is wrong and should not be emulated.

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Arlington, Va: When should I divide astilbe? And why does everyone say it's so easy to grow astilbe and Siberian irises, when they just don't thrive in our yard??? (We do have bumper crops of hostas, coneflowers, bearded irises and daisies, so I just don't get it.)

Adrian Higgins: It's getting late for perennial division, you don't want to divide just before it's going to bloom. Better to do both in late summer. Astilbe need evenly moist soil and partial shade and, in truth, would prefer to be in Connecticut rather than Arlington. Siberian iris thrive in moist soil, even waterlogged soil, but need sunlight for best flowering.

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Tree health: I noticed the maple in our backyard has a fair amount of dead wood, and many branches where it's leafed out but not all the way to the tips of the branches. Is this a sign of an ailing tree? Would you advise having an arborist come in, and how expensive might that be? Any other tips?

Thank you.

Adrian Higgins: Small leaves and branches that have not leafed out are indications of an ailing tree. It is still too early in the spring to make an informed observation. Trees can be restored to health by removing dead and diseased wood. Good arborists can be expensive, cheap ones can cost far more. I like the story of the one in Northern Virginia who dropped a tree on a house, said he would go and get help, and then never returned.

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RE: First Time Gardener: "The practice of placing mulch in a mound against the trunk or bole of a tree is wrong and should not be emulated."

Why? I see lots of people doing this.

Adrian Higgins: Because the bark composts and cooks the bark off the tree. Once a tree is girdled, its vascular system is gravely harmed. Also these mounds encourage root growth into them. When they are washed away, you have desiccated roots. They also provide a home for voles, which chew the bark.

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Norfolk, Va: Howdy Adrian! We've just recently taken down two old magnolia trees from our front yard and are anxious to get to work on our plans for a a lovely cottage-y garden at our bungalow. After digging out giant roots about 15 feet away from where the stumps were ground out so we could plant close to the house (the vines were wrecking the brickwork on my porch!), we're not looking forward to diggin up the roots that are closer to where the trees were. How long does it take for roots to rot away after a tree has been cut? And do those rotting roots add organic material or are they going to do damage to things I want to plant? Many thanks!

Adrian Higgins: I think you are safe to plant around the roots, as much as you can, and they will rot in time. I spent my Easter weekend planting six trees, about half the time was spent removing the roots of an old hemlock hedge, even though the stumps had been ground out. Moral: Garden projects are always more laborious than you think. I keep a powered grindstone in my shed and without repeated sharpenings of the axe, I would still be digging.

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Madison, Wis: What do you think of the White House grounds? Do you think there could be improvements made there besides who lives in the west wing?

Adrian Higgins: What a leading question. The front fountain doesn't do much for me. Alice Walters has been lobbying for years for a fruit and vegetable garden, which of course would be wonderful. The difficulty is that the incumbent is there 8 years at most, too short a time to do much. I would love to see a handsome fruit and vegetable garden installed. Why not bring back sheep and perhaps some cattle on the south lawn?

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Arlington, Va: We planted a japanes maple late last summer in a partially shaded area -- during the fall/winter, all the leaves curled up and fell. Right now, there are no leaves on the tree, but I do see some budding (but no leaves) -- am I in trouble?

Adrian Higgins: My acers have leafed out now, so keep your fingers crossed.

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Capitol Hill, Washington, DC: Good morning:The last two springs I have fought against some sort of weed that seems to be a wild onion. There are green shoots and small bulbs which, if I let them, grow to quarter size. I'm not really winning the battle, so I'm thinking I should concede and perhaps eat them... are they poisonous and/or tasty?

Adrian Higgins: These are wild onions, and you do have to dig them out or they will multiply beyond a joke. SOme people eat them, but they are not a part of my diet, nor ever will be. There are far better alliums to savor, including garlic and chives.

A fish tail weeder used for dandelions will be a useful tool.

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Asheville, NC: Our lawn has developed a serious moss problem where it would have been reasonable to expect grass. The lawn had been re-seeded a couple years ago, and we have an irrigation system. There is also almost constant sun on the lawn, which I'd have thought would not encourage moss. Were we likely given inferior seed, or are we watering too much? Or could there be something leaking into the water? It all seems so odd.

Adrian Higgins: You may have moss because you are overwatering and killing the grass. Moss also grows on compacted and poorly drained soil. YOu can try again in September after fixing the soil compaction and drainage, or cultivate a moss garden.

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Charlotte, NC: We have a section of our property that has trees and gets what I'd call "dappled sunlight." We also have two very large dogs (combined weight 275 pounds). Right now that area is covered with pine straw but we'd like to put in some ground cover that will grow quickly and need relatively little work to maintain in this environment with clay-like soil, hot and humid summers, and, of course, the dogs. What should we be considering as ground cover?

Adrian Higgins: Lots of choices in North Carolina but whatever you plant, you will have to fence off the area at least until the plants are established.

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Silver Spring, Md: Good Morning!I bought a honey suckle vine from a large home improvement store. It didn't have leaves when I bought it and now it just looks like sticks in the ground. Will it revive? Or did I make a bad purchase?

Adrian Higgins: A dormant woody plant will appear green if you scratch the bark with your thumbnail. If the underlying cambium is brown and the branch is brittle, move on to another plant.

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Alexandria, Va: Hi, Adrian. I have a red-headed woodpecker outside right now assaulting one of our trees. It's a large tree; can the woodpecker do enough damage to harm/kill the tree? Can you suggest remedies to keep the woodpecker away? I've already wrapped some aluminum foil around the tree. thanks!

Adrian Higgins: No, sapsuckers are more destructive, just enjoy the bird, which is beautiful.

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Maryland: Hi there, What's this purple-blooming tree I am seeing everywhere today?

Adrian Higgins: It is either lilacs coming into bloom, wisteria climbing in trees or the empress tree, pawlonia.

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To mulch or not to mulch: I keep hearing different things about mulching. When should I mulch and are there any specific guidelines I should follow?

Thank you!

Adrian Higgins: I'm piggybacking on this to add to the last answer. Are you talking about redbud? A fine year for redbud. Mulch is good if you spread it no more than two inches deep. Some gardeners dislike shredded hardwood mulch. I prefer something called pine fines.

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Arlington, Va: Hi Adrian, thank you for taking my question. Each fall I plant daffodil bulbs under a fifty year old dogwood tree. They bloom well the following spring, but the next year, produce more leaves than flowers. The tree is not very full, so I think that there is enough sun. Is there anything that I can do to help them produce more flowers?

Adrian Higgins: By far the greatest limiting factor in diminishing daffodil blooming is a lack of sunlight. It is also important not to cut off the leaves after flowering, or to tie and furl them. They are energy producing machines and need to do their work. It is conceivable that if the ground is waterlogged, the bulbs are rotting.

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Huntingdon Valley, Pa: Adrian, Glad that spring has arrived and our thoughts have turned to gardening. I've accumulated ash from using my fireplace this winter. How safe is it to use on my lawn and how much can I spread on the lawn? Thanks for your help.

Adrian Higgins: A little is fine, perhaps at a rate of a cup every 25 square feet (5 x 5).

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Re: purple tree: Isn't it redbud?

Adrian Higgins: See answer on mulch.

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Silver Spring, Md: Mr. Higgins: I have screens of Leyland Cypress on each side of my backyard that I planted 5 seasons ago when they were about 4 feet tall; most of them exceed 15 feet. The weight of the last snowfall of this winter caused two of them to lean heavily to one side, not quite uprooting them. They do not appear to be righting themselves. They are too heavy to pull back and stake upright. Any suggestions for preventing them from eventually falling over completely?

Adrian Higgins: You might stake the leaners, but do it with proper tree staking materials designed to prevent the line from digging in to the bark. And also trim off, lightly, some of the offending foliage. The new growth should fill in this season. These trees are not borne of nature but by hybridizers and have relatively small root systems compared to their top growth.

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Medina,Ohio: We bought an agapanthus bluestorm from White Flower Farms five years ago and it did bloom the first year but never again.Because of dividing we now have three plants. Over the winter we put them in a sunny window in the basement and the foliage grew to about 16 inches. Should this be cut off and what can we do so it will bloom? Your chat is the best reason to read The Post on Tuesday!! Thank you.

Adrian Higgins: Agapanthus would not be hardy in Medina, I would think. You would need to winter them in a cool room but protect them from freezes. We are out of time. See you next week.

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