The Garden Plot

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. (U-Street Neighborhood): Now that Autumn has arrived... does this mean I change my feeding/watering schedule for my houseplants?

How often should I water them?

Adrian Higgins: Yes, you should water less and feed less. Continued feeding, especially overfeeding, will continue to produce succulent growth that is tender to cold and inviting to leaf sucking insects. Also, you want the plant to rest over the winter and you help promote dormancy by withholding feeding. You might feed weakly once or twice a winter, but you should cut way back on fertilizing until the spring. Spray houseplants outdoors with insecticidal soap before bringing them indoors.

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Capitol Heights, Md.: Hello Adrian!
In our backyard there is a tall tree smack dab in the middle. When we venture out there we get attacked by so many mosquitoes. We want this tree to come down because of them, and because the grass will not grow in certain spots. Until we can get rid of the tree, what can we do in the mean time about the mosquitoes? On more thing. Is there a website that I can check out some backyard ideas? Thanks

Adrian Higgins: The tree may be a perch for mosquitoes, but it is not the cause of them, and taking it down won't reduce the mosquito population. Mosquito populations are directly related to the availability of standing water. This may be in unlikely spots, such as a gutter that has backed up, or trash can lids left facing upwards.

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Fairfax County, Va.: My neighbor sprayed Round Up to kill some weeds in his yard and it seems to have gotten on my variegated dwarf azalea bush. About 1/4 of the leaves (on one side of the bush) dried out and dropped off, but the rest of the bush looks healthy. Is there any hope for this plant? If so, what should I do to keep it alive? Or should I just dig it up and plant another one?

Adrian Higgins: The Roundup is unlikely to be the culprit, established woody plants do not find Roundup anywhere near as lethal as herbaecous plants. That said, you don't want to go around spraying them to find out. Also Roundup works systemically so it is unlikely to show just localised damage, I would think. Also, azaleas naturally lose many of their old leaves in the fall, manifested with yellowing and dropping on lower areas of the branches. Yours, however, seems to be in definite distress. Don't cut back branches unless oyu know they are dead, and keep the shrub watered but not soaked. One final point: Roundup will kill your neighbor's cherished perennials and annuals and grasses so you have to be very careful in its application. Avoid spraying weedkiller on windy days.

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Fairfax, Va.: I have a butterfly bush in my garden that has grown too wide and somewhat straggly. It didn't bloom as well this year as last (my only seasons' experience with it as we've only been in the house for a year and a half). Can it be pruned to help its shape and size, as well as improve blooming? If so, how and when?

Adrian Higgins: It takes a couple of years for buddleias to reach good blooming size. They must be sited in a bright, sunny location. If yours is in too much shade, move it in December to a sunnier place. Trim it a little when you do this, but cut it back to about two feet in February.

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Arlington, Va.: I love daylillies, but now am very afraid to divide them. Two years ago I divided a bunch of double-headed daylillies that came with my house and had not been divided for at least five years. They re-bloomed beautifully the year after, but only leaves came up in the old space this year (transplants in a different spot just started blooming, sparsely, this year). Last year I divided another bunch of daylillies in another part of my yard and a few leaves came up this year but no bloooms and now even the leaves are gone from that spot. Another bunch about a yard away, which I did not divide, bloomed well this year. Could I be dividing harmfully or is there some other problem my daylillies might have?

Adrian Higgins: Your question is a little confusing, but their blooming is dropping off not because they were divided but because something else is going on, either the soil is too poor, there is too much shade, or the plants are being stressed with heavy infestations of thrips or spider mites. Address these issues and even young divisions will bloom heartily.

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Huntsville, Ala: I have a witch alder (fothergilla "Mt. Airy") that I planted this past spring, and have been enjoying the blue-green foliage since then. I am eagerly awaiting the onset of the famed autumn foliage, but what's happening instead is that some of the leaves are getting large dark spots. The affected leaves are turning a slight yellowish color and then dropping off. The rest of the shrub looks fine.

I'm giving it the same acid fertilizer I give my azaleas, etc., is there anything wrong with my shrub? Is this a natural thing for autumn?

Adrian Higgins: Some witch hazels, which are closely related, are coming down with anthracnose leaf diseases and I wonder if the same is happening to your fothergilla? I would take a leaf to your local extension office for a diagnosis.

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Arlington, Va.: I have a hanging basket with impatiens in it. They are beautiful and I am going to hate to see them die. Is there a way to keep them going inside my sunroom? Or won't it be warm enough even if over 65 degrees?

Adrian Higgins: You could try but unless you have a cool, humidity controlled and bright greenhouse, the impatiens will becomes increasing ratty as the winter months progress. Much better to have a commercial grower to raise a fresh one for you to purchase next May.

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Takoma Park, Md.: Why do spiders build such enormous webs at this time of year? They're weaving huge webs that stretch between my garden and garage, but I mostly only see them in late August-early September.

Adrian Higgins: This is the work of the garden spider, which grows large at this time of year and correspondingly builds large webs. I think they can be beautiful and think of all the mosquitoes that might get ensnared in them.

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Alexandria, Va.: I missed the chat last week because I was hanging out with the wild ponies in Assateague, who kindly visited our tent at 1 a.m. and munched up lots of grass, all the while providing us with the soundtrack of their own internal composting going on! (Is it illegal to take manure out of a national park?)

At any rate, I did manage to catch the article you wrote. I am interested in severely cutting back the mature crepe myrtles in our yard, which each have about 20 trunks, in order to provide a bit more light under the canopy. Any thoughts on what fraction I could take out in a given year? Ideally I'd like maybe 4-5 trunks for each.

Adrian Higgins: The standard advice is not to remove more than a quarter of the top growth in any one year. I took out more than that with mine, but it was either that or fell the whole thing. This may cause suckering, but I am going to remain vigilant in removing resulting growth.

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Frederick, Md.: I hate to ask a butterfly bush question because you already answered one but: I have a smaller version of a butterfly bush. It only grows about three feet tall. How far back should I trim it this winter? Also, can I plant anything under it? Thanks!

Adrian Higgins: This must be a very dwarf variety indeed. Proportionately, you would probably cut it back to about 12 inches in late winter. I like to see them emerging from perennials that hide their bare ankles but it does get really shady underneath a buddleia, which is something to consider in selecting a companion planting. Hostas might be a good choice.

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Logan Circle, Washington, D.C.: On a recent morning I awoke to find that 14 of my dwarf boxwoods, which had formally defined a bed of roses, were stolen from my small, gated, urban front yard.

Based on their expense, I am reluctant to replace them in kind (unless you might have some suggestions for preventing boxwood theft). I have given thought to barberry, which would probably get too large, and am considering going the herbal route. Please give me some guidance!

Adrian Higgins: Try rue, which has an irritant in the sap that might discourage plant thieves, who are of a low order in my book.

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Annandale, Va.: Hi Adrian,

Last week you advised someone that if rats were a concern in their area, it would not be a great idea to have a compost heap. We don't have rats (as far as I know), but we do have voles or something similar (haven't seen them, but see their tunnels). Would you advise against a compost heap under these circumstances? Does it matter that the composting would be done in a bin-type contraption (purchased through Fairfax County) rather than as an uncovered heap?

Thanks for your help!

Adrian Higgins: Bins certainly are more animal proof than open piles. Your holes may belong to voles, chipmunks or moles, all of which should not stop you from having a compost pile.

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Scarsdale, N.Y.: When is the best time to trim bushes and trees (both evergreen and deciduous)?

Adrian Higgins: I think you can do a light trimming at any time but it terms of a drastic pruning, shearing or shaping, I wouldn't recommend that after late summer because it will encourage fresh growth that would be harmed by the frosts of fall. Winter dormancy is a good time to prune any deciduous or broadleaf evergreen shrub or tree, though most of the growing season is also a good time. Just not at this moment. Recognize too that any wood removed after mid summer from spring flowering shrubs will be removing flower buds.

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Fairfax, Va. RE: butterfly bush: Thank you for posting a reply. The bush is more than a couple of years old (it was there, and quite large, when we moved in) and gets plenty of sun. You say cut it to two feet -- this thing is easily seven or eight feet tall and about as wide. Should I still cut it so severely? Will that keep it more compact (assuming I keep up with this sort of late winter pruning)?

Adrian Higgins: Yes. In February, cut it back down to 24 to 30 inches and also remove some of the crossing congested stems entirely.

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Burke, Va.: Hi there. In June, I had some work done in the backyard of my townhouse. They planted two 3-foot tall plants (nandina and andromeda) and two staked climbing plants (clematis and hydrangea). They all seem to be doing fine. Do they need any special care/prep this winter? I am afraid they are not well enough established for standing snow. How about ice? Any tips would be appreciated.

Adrian Higgins: As first year plants, they won't be as winter hardy as established ones, so you may want to give them a protective mulch (which is removed in March). Be ready for some dieback in the top growth, but all should regrow as long as the roots have not been killed. I would give each a good soaking before the ground freezes and consider applying an anti-desiccant to the leaves of the pieris and nandina.

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Washington, D.C.: Hello! Our company just moved into new offices. My cubby has zero natural light, just the usual overheads. I crave greenery to give a touch of life to my spot, and a connection to the natural world. Any hints besides sanseveria? Any resources you'd recommend? Thanks.

Adrian Higgins: Some of the local large independent nurseries have a good selection of houseplants grouped by sun and shade and you might want to check them out to see what takes your fancy. Offices spaces also tend to be dry in winter, which promotes insect problems.

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Kensington, Md.: Mr. Higgins,

In January I sent my 87 year old grandmother a gardenia plant -- her favorite plant but one with which she had a bad history of growing herself (unbeknownst to me at the time). Well, this one is thriving and enjoys lovely views of the Delaware River while being misted daily. Alas, it is so happy that the time has come for repotting. My grandmother has decided that my husband is the only one to trust with the repotting effort though he has no experience with houseplants. Can you provide some guidance as to what kind of soil and food we should give the gardenia to continue to thrive indoors? Failure would be a disaster for my dear gram.

Many thanks!

Adrian Higgins: Select a pot that is a couple of inches larger in diameter than the current one. Whenever I repot a plant I like to put it in a new soil mix. It may react to the repotting by dropping some of its leaves. Make sure it is placed in a bright cool room, again with decent levels of humidity. Gardenias hate to be in dark, overheated indoor rooms in winter.

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Arlington, Va.: Adrian -- Thanks for answering my question. I am planning to convert a 10x10 area of our yard that is now a dirt pile into a garden. The area is part shade getting most of the morning sun. Can you recommend the best plants for the garden that our native to this area and the best place to go to find them?

Thank you.

Adrian Higgins: This is a small, shady area. I would be careful not to put in large shrubs, and keep the plantings simple and restrained. I would perhaps plant a native deciduous azalea and surround it with ground covers such as native gingers and Allegheny spurge. Green Spring Gardens Park in Alexandria has a native plant trail, where you might get some ideas.

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Ellicott City, Md.: We have a stone wall in front of our house that is completely covered with ivy. The ivy creeps into the garden and strangles everything, so we've determined that we need to get rid of it. What is the best way to do so? Do we really have to yank it all out one strand at a time?

Adrian Higgins: Yank it out, one strand at a time.

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Del Ray, Va.: Hi Adrian,

I bought a home which had been neglected for many years. We just removed six very overgrown bushes, (an assortment of hollies, forsythia and someting with a tiny pink flower). What should I add to the soil to amend it? The front yard is very sunny, facing south and I plan on putting in a nice mix of perrenials and annuals, as well as bulbs.

Also, there is a hedge of azaleas that has been clipped into a 15" wide by 24" tall shape for years. The leaves seem spotty. Is it worth it to transplant these to another spot or just rip them out and start over? I'm afraid they may be too dense.

Adrian Higgins: The azaleas sound congested, both as a group of plantings and as shrubs that have grown dense in leaf. This may contribute to your leafspot problems, though I suspect you are describing lacebug damage. You could salvage the azaleas by selectively pruning out branches and replanting in part shade, good soil and with lots of space. I think you might be better off ditching them. however.
I would throw in a shrub or two, however, perennials, annuals and bulbs alone may not give you sufficient height or structure to a bed, or season round interest.

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Gaithersburg, Md.: Hello! We have sycamore trees lining the road in our neighborhood. For the last two years, beginning in mid to late summer, the leaves start browning and falling off. As of today, the trees have lost half their leaves, while the other hardwoods in our neighborhood are still green. Any ideas? They're pretty unsightly.

Thank you!

Adrian Higgins: Sycamores are susceptible to a number of leafspot diseases, especially in cool wet years such as this one. The trees should spring back next year.

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Takoma Park, Md.: I need help! I've moved into a bungalow where a recluse use to live. I've worked on the front yard but the back yard (about 25 x 50) is literally a jungle with years of leaves and no grass, just weeds and loads and loads of catalpa seedlings! I just don't know where to begin. I've cut back the larger catalpas (about five feet tall and about an inch or two wide), but because of their numerous stumps and vines I can't use a lawn mower. I've been weed wacking but even that doesn't do it. I can't even get landscaping people to return my calls! I want to get down to the bare bones but honestly, don't know what I will do when I get there. I've been saving loads of newspaper to lay down and hopefully mulch over to kill off all the weeds? Any advice?

Adrian Higgins: I would buy a sharp shovel and dig out the catalpa seedlings. Reclaiming overgrown yards is a matter of devoting a series of weekends to weeding and digging out offending plants. You will also need a good pair of pruners to cut back all the vines and other untamed vegetation. Do look out for poison ivy. In time you will conquer this space and as you work, you will form ideas in your had about how to plant the space.

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Silver Spring, Md.: Neophyte home owner here with probably "doh" question -- but this is the first lawn I've had so I know nothing.

I'm planning on doing the fertilize -- re-seed thing to the lawn this weekend (if Hurricane Jean cooperates).

Which goes first and do I have to wait in between?

I'm guessing fertilize first -- but can I immediately put down the seed or is there proper sequence?

Help?

Adrian Higgins: Contrary to the lawn industry ministrations, you don't need fertilizer to get grass seed to germinate or grow, and indeed excessive chemical fertilizer will burn seedlings. Grass seed needs good soil contact and constant moisture to germinate and, preferably, two inches of cultivated soil in which to set down roots.

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Gaithersburg, Md.: I have morning glories on a pot on my desk and they have trailed and bloomed very nicely. Although the seed envelope said they are annuals, my neighbor insists that they are perennials. Can I keep them in the pot and they will grow next year?

Adrian Higgins: No you can't keep them going but if they are heirloom varieties, you can gather the ripe seeds and save them in the refrigerator for sowing next May.

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Arlington, Va.: Hi Adrian,

With all the wet weather, I've had some erosion in my yard exposing the larger roots of two large ash trees. How much top soil should I apply on top of the roots and how close to the tree so that I don't damage the roots. I want to replant grass as close to the tree as possible.

Thank you very much.

Adrian Higgins: Most of the feeder roots of this tree are several feet removed from the trunk, and you would not want to smother them with lots of soil. If some of the soil has washed away from the anchoring roots near the trunk, you could backfill those pockets but don't go overboard.

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Aldie, Va.: I have a question about my lawn. It has lots of weeds in it and the grass looks burnt (brownish). What can I put in it to treat it. I have no green thumb at all, so you will have to bear with me.
Thanks

No Green Thumb

Adrian Higgins: There are a million things that could be harming your lawn, including grub damage. Look up the Maryland Home and Garden information center website, go to online publications, and read about renovating lawns, which is done at this time of year. You should also get a soil test so you know what deficiencies in pH and soil structure you have to correct. Dumping seed on hardpan will be a waste of time and money, unless you enjoy watching the birds feed. Alas, we are out of time again. Another marvellous day to be in the garden. Savor it.

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