The Garden Plot

Gardening

Adrian Higgins (The Washington Post)

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."

Editor's Note: Washingtonpost.com moderators retain editorial control over Live Online discussions and choose the most relevant questions for guests and hosts; guests and hosts can decline to answer questions.

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Washington, D.C.: I have a prolific rosemary bush in the yard. Maybe 4 feet tall and 3 feet wide. How much and when should I cut it back before winter if at all?

Adrian Higgins: You shouldn't cut it back, short of harvesting stalks for the kitchen. Rosemary is borderline hardy and the more cutting you do, the less hardy it will be, especially if this winter is a stinker.

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Takoma Park: Sigh...

My wife and I spend a decent amount of time making our apartment complex's groungs looking nice. The landlord even says so.

Unfortunately, he forgot to remind the landscapers he hired to to a fall "clean up" of the beds. They cut down EVERYTHING! The fennel, the fall grasses, the late blooming stuff. All gone. Then they covered the grounds with a mulch/bark mixture.

Since I cannot kill anybody, is there anything I can do to give the area something? I put four mums in but the bed just looks SO barren.

Thanks

Adrian Higgins: I feel your pain. Certainly, you can install some mums that will have some show probably through to Thanksgiving.

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Cheverly, Md.: Hi there! Should I dead-head my butterfly bush one more time in the hope of another round of blooms, or leave it alone to guarantee visual interest through February? (when I will cut it back to 3 feet as advised)

Thanks.

Adrian Higgins: It won't cycle another bloom now from pruned wood. Just enjoy what's left and let it be. Better to cut it back toward the end of winter than at the start, again for hardiness reasons.

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Greenbelt, Md.: Dear Adrian,

Two questions please:
1. I planted grass seeds under some big trees about three weeks ago. The seedlings are growing nicely (about 3 inches tall now). However, a few leaves have fallen here and there. When can I start raking leaves in that area? Is there anything I should do to prevent the seedlings from getting damaged?
2. I would like to plant some incense cedar in partial shade. Do they grow well in our region? Or should I consider cedar green giant instead?

I appreciate your advice.

Adrian Higgins: Blowers are a nuisance at this time of year but they have their value. New grass should be kept clear of leaves and a blower is a good way of doing that without stomping on the seedlings, which you would have to do with a rake.

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White Plains, N.Y.: Any ideas about a rose that just won't bud out? This plant has been in the ground 2 - 3 years. I got a few flowers early in the summer, but since July, all I am getting is growth and more growth. I even tried to whack it back a bit by pruning it at a 5 leaf branch. result: more growth. Any ideas as to why and any suggestions for bettering my predicament for next year?

Adrian Higgins: Some roses, particularly old garden roses, bloom once. This is annoying, because modern roses just keep blooming. The counsel from old-rosarians is that some of the most beautiful and fragrant roses of all are once bloomers, and since we accept once a year bloom from other shrubs such as camellias or tree peonies, why not from roses? In your case, it may be that your rose is being shaded out by encroaching shade. Roses need at least six hours of sunlight.

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Bethesda, Md.: Hi Adrian,
We have a very large, mature Black Walnut tree which grows quite close to our house. I'm not in love with the tree -- it is very messy, shades the yard and presents challenges for gardening near it. However, it is healthy and a native tree and I can't bring myself to take it down. How much could it be trimmed without irreparably harming it? Are there important questions to ask an arborist so as to avoid creating more problems than already exist? Thanks so much.

Adrian Higgins: You don't want to remove so much wood that the tree becomes misshapen, or is forever sprouting water spouts. Certainly, though, you could do some aesthestic trimming. Probably better to wait now until the tree is in winter dormancy, when you will see its branch structure better.

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Woodbridge, Va.: We still have not mulched our beds -- is it too late? I don't want to trap cold under the mulch. We have coreopsis, azaleas, and some green shrubs with shiny green leaves. Thanks.

Adrian Higgins: There are two schools of thought: one is that you mulch before the soil gets cold to keep the roots warm and growing. The second is that you mulch after a freeze so that you keep the ground cold and the plants won't break winter dormancy too early. I think if your beds need mulching than any time is better than no time. But you only need a couple of inches at most and be careful not to get mulch up against trunks or smothering the crowns of multi stemmed shrubs such as boxwood.

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Bethesda, Md.: I have a serviceberry -- I think the cultivar is Autumn Brilliance -- that has become quite leggy. It's a 10-foot-tall stringbean. Not sure whether it is stretching because a big house went up on the property behind ours this year, or I just sited it badly when I planted it two years ago. There are three trunks, each about 2 inches in diameter. How big a rootball do I need, if I decide to move it?

Adrian Higgins: I think if it is only in for two years, you can still move it. I would dig a rootball that it as least 36 inches wide. YOu can drag it on to a tarp and haul it to its new location. No need to ball and burlap it if you are replanting right away. Make sure the feeder roots are well soaked and put down a light mulch.

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Washington, D.C.: Hi Adrian, I'm submitting early because I really need help. My houseplants seem to have mites -- I don't see them in the plants themselves, but occasionally they are covered with black scales and are very sticky with sap. A spray with plant oil usually fixes the problem for a while. However, the soil in the pots is absolutely infested with tiny white bugs, and nothing seems to get rid of them.

I'd like to solve this problem before I bring the other plants in for the winter -- what can I do? Thanks.

Adrian Higgins: I think you might have mealy bugs, which, once they get into the soil, are very difficult to kill. You do need to address it before you bring the plant in, though, unless they spread spread to other house plants. One method is to fill a bathtub with warmish water, give it a squirt of detergent and plunge the pot into it. Do this overnight, but don't forget about it. The next morning repot, hose off the soil and repot the plant using a fresh potting mix.

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Frederick, Md.: My plants don't seem to know that it's fall. Everything is blooming again! Butterfly bush, roses, and English daisys. I'm a fairly new gardener so maybe these plants are supposed to bloom now?

Adrian Higgins: One of the delights of gardening is in discovering late season plants that bring a new complexion to the garden when you think all is finished. We used to rely on mums alone for this but have come to learn that other shrubs and perennials can really stretch the season and make it interesting even after the first frosts.

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Centreville, Va.: Dear Adrian --

I'm planning to set up a raised bed this weekend to plant some late season lettuce and peas.

What's the best way to fill it?

Thanks!

Adrian Higgins: You might be hard pressed now to grow lettuce and peas without protection. Other greens are better suited to post frost cultivation, including spinach, chard, kale, and mesclun greens such as beet greens, mache, and radicchios. I advise people to take cedar or even untreated pine plank, turn them on edge, peg them with wooden stakes, and backfill these boxes with your own screened compost and/or purchased material.

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Fairfax, Va.: We have a few hydrangea plants that grow well (and fast) but get very large each year (3-4 feet high and 3-4 feet around), and never produce the lovely blossoms I see on hydrangea bushes in other people's yards. What's the trick to getting these to bloom?

I do trim them back every year usually in the late winter/early spring (someone once told me that blooms only come out of second-year wood). I wonder whether I trim them back too far (I cut them back leaving about 1 foot left) or at the wrong time of year. But if I leave the plants go, they will get way too big.

Any suggestions on how to get them to bloom?

Adrian Higgins: Your pruning regimen is at fault, I suspect. Hydrangea buds for next years flowering stems have been set, already. Remove them, and you remove the blooms. Since hydrangea also is marginally hardy, you afford htem better protection against winter dieback by not pruning them. YOu can prune off the dead stalks in April when you see the new buds erupting. Also, if a hydrangea has grown old and thick, you should thin it out by removing whole stems. I would do this after blooming.

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Arlington, Va.: I want to improve the soil in my garden and am planning on growing some green manure. Is it too late in the season to sow hairy vetch and winter rye seeds? Will I have any luck growing these crops over the winter?

Adrian Higgins: Both of those cover crops are winter hardy and would be well sown now.

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Help help! Bulb idiot!: I live in Ashburn -- can I start planting now, or is it still too warm out? When would you suggest I start?

I have 160 bulbs, which sounds like a lot, but is it, really? I want to make the front yard near the stoop a blaze of color, and out back, around each deck post (3) make a swath of color about 2 feet in diameter around each one. Maybe 3 feet in diameter.

Any rule of thumb? How many more should I buy, for the posts coverage?

Adrian Higgins: You will get a good show with 160. Of course 160 big tulips will read more than 160 snowdrops, you don't say which bulbs you are picking. I've always described groupings of like varieties as drifts, though I heard a better term the other day: Puddles, you want puddles of color. If they are framed by border or paving, all the better, it should be crafted as a scene. Don't plant anything in a straight line unless you have to. I think the rule of thumb is four big daffodil or tulip bulbs per square foot, as many as nine or more of smaller bulbs.

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Springfield, Va.: When is the last date to plant ornamental grasses, peonies and hydrangeas this fall?

Adrian Higgins: Now is a good time. Materials grown in pots will transplant well. Digging from transplants is more tricky, and most grasses don't move well now and are better dug and moved in late winter.

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Charlottesville, Va.: We have a deciduous magnolia, saucer I think, that has lots of water spouts. I remember asking earlier and being told not to cut them off during the growing season. When would be a good time to do this?

Also, a weeding tip: I read some years back -- perhaps your suggestion -- about using newspaper under mulch to reduce weeds. This is the second autumn I've done this, and it works well. I put down newpaper a few sheets thick, arranging it around the plants, and place mulch over it. It covers up those horrible little weed seedlings that are coming up now and continues to work into the spring. It's also a great way to recycle newspapers.

Adrian Higgins: Thanks for the tip. Using sheets of newspaper covered with compost and mulch is a good way to build up poor soil and keep back weeds while you do it.
I would wait until winter dormancy before removing the water sprouts and then keep on top of them next year.

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Chevy Chase, Washington, D.C.: Hello Adrian:

After reading about Phlox a while ago in your column. I ordered 15 bulbs.
Hardy Phlox and Dwarf Phlox. Would you please advise me on planting instructions?

Mulch appreciated

Adrian Higgins: Commonly, there is creeping phlox, a woodland perennial that flowers in April, and garden phlox, which is the upright showy flower of the summer garden. Both can be planted now. Garden phlox needs a sunny, well drained location with good air circulation. Even then, it is a martyr to disfiguring powdery mildew. I would only plant varieties that have been bred to resist mildew. To plant them, cut back the top growth and set the roots and crown in good cultivated soil. Water well, and mulch a little.

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Dupont Circle, Washington, D.C.: My enclosed backyard is a cement pad big enough for two cars. I only have one car, and I'd like to dig up half the cement and replace it with a small garden. Friends thought that would be expensive and suggested I build a raised bed on top of the concrete instead. I think I'd have poorly drained soil and lots of unhappy plants if I did that. What do you think? Can plants be happy in 6-8 inches of soil above a concrete pad?

Adrian Higgins: I think that would be tough. You would be better off investing in nice large wooden planters and creating a garden of those. Go to the US Botanic Garden and look at some of their outdoor planters to get a sense of the style and size that you need.

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D.C. re: black walnut trees: FYI, there are some injections that can be given to the roots of these trees to make them fruit significantly less. Also worth asking an arborist about.

Adrian Higgins: Thanks. Other trees can be sprayed to prevent fruit and nut set, including ginkgos and sweetgums.

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Hyattsville, Md.: I've got a good crop of butternut squash this year which has spread across my back lawn. Many of the squash have developed large patches of discolored, thin, "scabby" skin where they were in contact with the grass, however. I have cut open affected squash, and the flesh seems perfectly normal. Any idea what causes this? Could it spread through the skin to the flesh if fruit were left on the vine longer?

Adrian Higgins: It might be either squirrels or wasps rasping at the skin. As long as the shell is intact, the meat inside should be perfectly useable.

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Arlington, Va.: Adrian,

Early this spring, I cut two azaleas down to 30 percent and both of them are doing well.

I have four other plants that are way too big for the foundation planting beds in which they sit. Can I cut these azaleas down in a similar fashion now or should I wait until early spring?

Thanks.

Adrian Higgins: YOu can cut them now, though it would be safer perhaps to wait until after dormancy in December. You will lose flowers in doing this, but the azalea has so many, you're not really affecting the show.

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Arlington, Va.: We just moved into a house, and some contractors told us there is some poison ivy mixed in with English ivy (or whatever that nonnative plant is that takes over everything) in the yard. We got a landscaper to have a look, and he'll pull it all out for us. He said, though, because the poison ivy leaves are drying out, he can't spray it, since the plant has hit dormancy. My question is whether it will come back in the spring, and what does it look like? Do we get it sprayed then and kill it for good? (Yeah, my spouse should have asked the landscaper, but it didn't happen.)

I'm from the west, and while I can identify poison oak yards away, I have no idea what it looks like in the spring. Also, is poison ivy common in yards? I never saw poison oak in a suburban yard in California.

Adrian Higgins: I would get a book that shows poison ivy, so that you can identify it. You don't want to get too close to it because the rashes are quite awful and persistent. It turns a beautiful red color in November before dropping its leaves. Now is a perfectly good time to spray poison ivy, indeed an optimum time because it is taking sugars from the leaf into its root system. If the leaves are drying out, it's because of dry conditions. Water it so that it is turgid and ready to accept Roundup.

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Alexandria, Va.: My mums and lily are in full bloom, but I don't know what to do with them when the weather turns too cold and they stop blooming for the season. Do I let the leaves die a natural death, cut them back, what? I know how to take care of my mums next year when they come back up, but not what to do this fall/winter. Oh, and I don't know what type of lily I have. It has narrow green leaves and yellow-orangish blossoms which last maybe a day. Is this your typical day lily?

Adrian Higgins: The latter is probably a reblooming daylily. Don't do anything to it. Mums are another plant that are a bit tender and by not cutting back the dead top growth come December, you enhance its chances of making it to next year. Also a mulch will help against frost heaving, in which the soil rises up and exposes the roots, which are then dried out with mortal effect.

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Burke, Va.: Hi Adrian -- My garden area of approximately 600 square feet is overrun with tall weeds. I do not plan to plant fall/winter vegetables or to plant any rye type cover crop. My question is: Will these weeds die almost completely to the ground in winter? What month can I then layer newspaper and mulch so my soil will thn be relatively weed-free for next spring/summer plantings? As you can see, I want to avoid the hard work of pulling up or hoeing these weeds. Thanks. I enjoy these discussions a lot.

Adrian Higgins: I don't know what the weeds are and yes they may well die to the ground, but first by spreading thousands of seeds that will make your job all the worse. The key to breaking the cycle of weeds is to kill them or pull them before they flower and set seed. Weeds succeed because they are prodigious, and they will defeat the gardener who is not willfully opposed to them. I would cut these weeds to the ground, little effort with a lawn mower or weed whacker, and then either cover the area with newspapers and compost/soil, or sow a winter crop such as winter rye. This will bully out winter weeds.

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Fugly Yard, Va.: Adrian,

My wife and I need your help! We can't stand the way our backyard and front yard look. We are looking for something simple, easy to maintain and doesn't attract bugs, but still look nice. ANy suggestions for plants/flowers?

Right now the front of our house has ugly bushes that just look random and I want to pull them (looks like a lot of work). The backyard just has 'stuff' growing here and there. I wouldn't mind planting something for privacy too.

I know, we are asking for a lot, but any wisdom would be great. THanks!

Adrian Higgins: I can't give specific advice without seeing what you have but generally, you have to decide what shrubs are overgrown, which can be pruned to rejuvenate them, and which should be removed. If a yard is wildly overgrown, it is best probably to clear everything and start again. Plants have a hierachy of use, with trees, conifers and large shrubs working as building blocks. Flowers, i.e. perennials, herbs and annuals, are the icing on the cake, but they are not the cake. One good explanation of this is in a book called The Book of Garden Design by John Brookes. See if you can get a copy on Amazon.com.

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Washington, D.C.: A large patch of my backyard turned brown and withered this summer, water and shade did nothing to help it recover. Now I have a 12 foot patch of dirt covered only by the crisp, brown remnants of the clover and grass which used to grow there. Even the juggernaut crabgrass and creeping Charlie adjacent to the bare spot are making no headway.

Adrian Higgins: I suspect you may have grub damage. If the lawn sheets back with no anchoring roots, that's the problem. You will need to resow the affected area and use a grub killing insecticide such as imidacloprid. Well, we have run out of time again. See you next week. Gets those bulbs in.

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