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.

He was online Tuesday, April 22-- appropriately enough, Earth Day -- to offer advice on your lawns, flower beds, vegetable patches and window boxes.

A transcript follows.

Catch up on previous 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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D.C.: Can you suggest a variety of lilac that stays compact and does well in a very sunny southern facing garden?

Thanks!

Adrian Higgins: Either Miss Kim, Palibin or Syringa x laciniata.

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Mt. Pleasant: I planted tulip bulbs last fall and (until the rainstorm) was really enjoying the riot of color in my backyard. Do I need to do anything to make them come up again next year? I know you said to leave the foliage alone until at least June -- at some point do I need to dig them up and replant in the fall, or can I just leave them to come up again next year?

And a mostly unrelated question -- I have a Japanese maple in a very shady corner of my yard. Is there any attractive groundcover I could plant around it, or am I better off to just lightly mulch that corner, being careful not to pile mulch against the tree?

Adrian Higgins: Unless you have known varieties of tulips that will come back reliably, I would just treat this bulb as an annual. Under my acer, I have planted Epimedium rubrum. It's superb.

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Container City: Can lavender and heather be successfully grown in containers? And are they hearty enough to survive Maryland/D.C. winters outside?

Adrian Higgins: Certainly lavender can but heaths and heathers find our climate too hot. They make fantastic container plants from September to May, however. You can then either plant them in a cool, shaded area or toss them.

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Fairfax, Va.: You may have addressed this before, and if so, my apologies. Everyone knows that you should not plant the same vegetables in the same spot every year, as that depletes soil nutrients over time. However, I really have no alternative for my tomatoes and zucchini because of sunlight and space.

I plan to roto-till dry cow manure, old rotted leaves from the fall, and peat moss this weekend, as I've done in the past. Is there anything else that you would recommend as a soil amendment process now and throughout the growing season? Does this effectively counter the effects of year-after-year same crop growth?

Thanks!!

Adrian Higgins: The only thing you have to watch for is the build up of blight spores in tomato beds, so do a lot of amending, and mulch heavily with straw, and remove blighted leaves as they appear.

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Arlington, Va.: Hi! I recently seeded my backyard after I mowed it (Saturday) to fill in bare patches. I've already started to see some new growth, but not in every place. When should I mow the yard next? I'm afraid of hurting the new growth or of letting the yard get too high.

Thanks!

Adrian Higgins: You should move seedlings once they reach three to four inches with the mower set at the highest setting. Buy a new blade.

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Legation Street: Adrian - I planted galium after learning about it from you a couple of years ago as a particularly nice ground cover. I love it, but I notice it is marching on my epimediums. Will it take over? Any thoughts on how to get them to live in harmony? A wall?

Adrian Higgins: It will spread in rich, moist soil. I'm surprised the drought didn't beat it back. You can simply pull it where it doesn't belong.

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Reston, Va.: How do we address soil in an organic community garden plot that needs help? Our zucchini flowered, but did not produce, and someone said that meant the soil was imbalanced.

Adrian Higgins: Zucchini may have failed to bloom if it's in a high nitrogen soil, but even then you should have had some blossoms. You may have had problems with a lack of pollinators. Any well balanced and well rotted compost is going to have the micronutrients that the vegetables need. You can also add rotted manures and kelp and alfalfa meal and bonemeal. All this will give you a fertile and balanced soil.

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Kensington, Md.: Good morning. I'm looking for some suggestions for shrubs to plant as a viewbreak along my backyard fenceline which gets mostly shade. Any recommendations would be appreciated.

Many thanks -- love the chats!

Adrian Higgins: Cherry laurel is an obvious choice. Also consider the Prague viburnum and camellias.

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Mt. Vernon: Dr. Higgins -

You always give such good advice that I hope you can help me. We have three dwarf butterfly bushes that are not doing well despite the fact that they get about 5 hours of good morning light. I would like to replace them with an interesting bush that will not get too big. There is a big oak tree, several leland cypress trees and an American holly tree behind them.

Thanks!

Adrian Higgins: Sounds like a lot of root competition and dry shade. I have grown osmanthus in such a setting, but it takes a while to get them established. Oakleaf hydrangea or Annabelle hydrangea might work as well.

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Silver Spring, Md.: I'm submitting early due to a meeting.

A month ago I planted 4 cherry laurels, specifically otto lukens, as a foundation plant. When I bought them all the plants available at the nursery had some leaves with holes in them. When I asked about this as a possible fungal infection I was told these were from "winter burn." I took them home and planted them. Now I notice that on all of them there are yellow and brown leaves and on three of the four the overall color is not as deep green as it should and the little flowers are not blooming as nicely.

I have not been watering every other day (as I probably should be), I have been letting mother nature take care of that and am wondering if this leaf issue is from my lack of watering or possibly a fungus.

Thank you so much for your help and for the chat!

Adrian Higgins: It can get a leaf spot disease. Good sanitation and good air circulation will help. Cherry laurels like even soil moisture but you must not water them every other day. They will rot away, guaranteed. One deep soaking once a month in dry conditions will suffice.

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Silver Spring, Md.: Mr. Higgins:

I've been thinking for a while about installing a greenhouse window -- you know, the type that juts out, and that allows seedlings, herbs and such to thrive over winter -- in the kitchen.

Do you have any experience with these installations? Are they effective, and do they cause a energy-saving troubles in the winter?

(Also, I very much enjoyed your community garden video. Highly recommend to all my fellow discussion groupies).

Best

washingtonpost.com: Community Plotlines (washingtonpost.com Home and Garden section)

Adrian Higgins: Yes, the community garden series promises to be fun and informative. These window inserts are effective, but as you say they can increase energy costs in winter. Another consideration is that in summer, the solar build up can be too much, and you would need to whitewash or screen it. I have not used one, I would perhaps visit some independent garden centers with large house plant sections, and talk to some of the people there about them.

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Alexandria, Va.: Can you recommend a small tree to flank my front steps? I wouldn't want it to grow more than 5-ish feet tall. Something that would look nice with holiday lights.

Adrian Higgins: Boxwood Dee Runk. Or dwarf Hinoki falsecypress.

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Silver Spring, Md.: I love your chats - thank you for all the great information.

I don't get much sun in my tiny townhouse front yard so a few years ago I had ground cover put in which is doing great. I usually blow the leaves out in the fall but this year I was advised to leave them there as insulation. Well, here it is almost May and I still can't get them out since it has been so wet. Am I running a chance of ruining the ground cover by not getting rid of the wet leaves?

Should I leave them there or get rid of them each fall?

Adrian Higgins: You need to remove the leaves, or at least chop them up and put them back as a mulch. You don't say what groundcover you have or the type of leaves (maple tend to mat more than oak) but do collect them before they rob the emerging groundcover of its light.

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Sterling, Va.: I'm considering planting a crape myrtle to act as a screen between us and a nosy neighbor - is now a good time to look at doing that, or should I wait until later in the year?

Adrian Higgins: First of all, reconsider the choice. A crape myrtle's canopy will rise and rob you of the screening you want. I would consider hornbeams, hophornbeams or Chindo viburnum. The last is evergreen and can get 20 feet high if it's happy, but you can keep it trimmed to the desired height.

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Hydrangeas Question: Is there anything special to do to hydrangeas to help them grow? I planted a few last year and they didn't come up much. Thanks!

Adrian Higgins: Water!

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Washington, D.C.: My little backyard has some lovely climbing roses that were planted by a previous tenant, but some of the leaves are spotty and yellowed. Any suggestions for keeping them healthy?

Thanks for the chats, I learn so much from them every week!

Adrian Higgins: You need to remove the yellow ones and bag them. Good sanitation is key to minimizing blackspot. I would also give them a preventative spray now of a copper or lime sulfur spray.

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Vienna, Va.: Hi, I never got around to planting a bunch of bulbs in the fall. (Yes, I am mortified at this!) What can I do with them until November?!

Anything?

Adrian Higgins: Throw them at the squirrels.

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Arlington, Va.: Hi Adrian. Is it the appropriate time to cut back my lavender? How much do I cut? Also, I'm looking for a nice groundcover to complement my hydrangea. Any suggestions? Thanks.

Adrian Higgins: You can trim lavender, but you must not cut them back hard. Keep a fair amount of the foliaged stems, no matter how ragged they look at the moment. They will spring back beautifully next month.

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Silver Spring, Md.: Hi, Adrian -- I got a notice that White Flower Farm has shipped my tomato plants. What do you think? Am I safe to plant them after hardening off for a few days?

Adrian Higgins: I think so. Keep an eye on the weather forecast and cover them if we get a chilly night. Make sure their bed is free draining and enriched.

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Takoma Park: Dear Adrian, Thank you for suggesting last fall that clematis "Guernsey Cream" might work on a north-facing wall. The small plants we put in are growing like crazy now and have lots of buds. Thrilling!

Adrian Higgins: Good!

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Trees in containers: My daughter received 10 bare root saplings from the Arbor Day people. We now have them in pots -- all survived. How long do trees survive in pots? How do we treat them? I had a cotinius that I kept small in a pot in Europe. Does the same apply to U.S. flowering trees?

Adrian Higgins: Cotinus is going to be easier to keep small than, say, a red maple. Growing them in pots will stunt their growth, but you also run the risk of them dying because our summer climate is brutal and keeping pots watered is a chore. The larger the pot, the better the chances of success. I would try and find a suitable spot to plant them, however, being mindful of their eventual size and site preferences.

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D.C.: Doggie Problem -- I have one dog that is driving me crazy -- he keeps urinating on my plants and shrubs. Is there anything I can do to prevent this? He has killed a few things and it's driving me crazy!

washingtonpost.com: If Adrian can't answer this one, check out tomorrow's Pet Advice discussion with veterinarian Dr. Michael W. Fox.

Adrian Higgins: Unfixed male dogs pee a lot to mark their territory. I don't know if he's had the op, but you should consider it. (For the dog, that is) The only other solution is to have the garden hose or watering can handy, and dilute the urine as it appears.

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Richmond, Va: Adrian:

Last fall I planted a number of Redbuds (forest pansy), watered them with a few gallons once week and mulched them lightly.

This spring they didn't bloom much, but are now leafing out well. They are all between 5 and 6 feet tall.

Any ideas on what could have caused the blooming to be so thin? Perhaps drought stress from last year?

Adrian Higgins: Yes, I'd say drought stress. Give them lots of water and scratch in a bit of high phosphate fertilizer.

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right-sizing a tree: We have a grassy 10-12 ft space between our and our neighbor's driveways. I would like to put a tree there, but would like a recommendation of something that won't get too big and scratch our respective cars as it grows. (If I could plant a big one that overhang the driveways and the cars, that would work, but it's tough to plant them THAT big.)

A redbud would be my first choice, but the mature ones look too wide and the branches hang low. Crepe Myrtle? Something I can prune back until it grows tall enough to clear the cars?

Adrian Higgins: Neither crape myrtle nor redbud would be suitable, I'd say. Again the upright European hornbeam would work nicely. Or upright yews, even.

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Fairfax County: Hi Adrian,

We have a really shady back yard (mature oak trees throughout the neighborhood), and our grass is getting gradually taken over by moss and some annoying tall bushy grassy something. We'd like to replant part of the yard. What type of grass will grow in shade in our climate, and when should we plant it?

Thanks!

Adrian Higgins: Few turfgrass varieties will do well in deep shade. You could try to cultivate a moss garden, or use ground covers Carex is a grass like genus that will take shade. See if you can get your hands on Timber Press Pocket Guide to Shade Perennials by George Schmid. You could also take out a few trees and still keep a shade garden, though this might be too expensive.

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Alexandria, Va.: I was wondering if you have read the book "Allergy Free Gardening" and what you think of it. I've recently purchased the book and am using it to guide me in selecting plants that supposedly don't produce as many allergens as other plants. I'm not certain the science is all that, but I figure it can't hurt.

Adrian Higgins: I think it's a load of baloney. Tree pollen travels for miles, so removing all wind pollinated staminate trees from your yard will have little or no effect.

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Central Pa.: Mr. Higgins,

In honor of Earth Day (and the end of our primaries!), I just joined the Arbor Day Foundation. As a part of the membership, I decided to select (10) Colorado Blue Spruce trees, to be shipped to my home (hardiness zone 5-6) sometime in the next month.

Knowing that the trees are going to be twigs, what is the best way to plant them and care for them for the next couple of years? I'm planning on keeping them in a fallow garden plot that receives full sun - what is the best prep for the soil, and what should I do to over-winter them?

Thanks - the ADF website has a lot of information for deciduous trees, but not much for the evergreens.

Adrian Higgins: If you have 10 Colorado blue spruces, you will need a property of about six acres I would say, to give them the setting they deserve. They may be twigs now, in half a century they will be 40 feet high and 20 feet across.

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Alexandria, Va.: We have a number of Roma tomato seedlings coming up, but not a lot of space to plant them in the ground. If we put them in pots, how much room will the roots require? Would a window box (say 6-7" deep) provide enough space?

Adrian Higgins: Barely, you could put three to an 18 inch pot, and grow them on stakes. Tomato vines and window boxes really don't go together.

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Fairfax, Va.: Thanks for taking my question, do you have any suggestions for a "green" solution to our dilemma? We have a small fenced backyard (in a townhome community) that we would like to make more "homey" with native plants and trees to ensure we're doing our part of not wasting water, etc. It's a complete blank slate right now and we're eager to get started.

Adrian Higgins: The key is to build with plants that will remain in scale. I would visit Fern Valley at the National Arboretum and get a sense of mature sizes and ground covers that you find attractive.

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Great Falls, Va.: Hello Adrian -

Thanks for the great chats! A question about Empress of India Nasturtium. I've been growing them from seeds for a few weeks now and they were thriving... until I put them out in the sun on Saturday during the warmest part of the day. When I took them inside around 4 p.m., they looked as if someone had stepped on them.

Their stems look withered from the soil upward, with the parts nearest the leaves still plump and healthy. I've nurtured them since and some have revived, but not all.

Quite a mystery. Any theories, appreciated!

Adrian Higgins: They may have been set back by the cold, or beaten down by the rain. Make sure their soil is not waterlogged.

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New York, NY: I'm looking for some flowering vines for a small (10 x 12) patch of concrete that we call our backyard. The place gets sun from about 10:30 AM to 1:30 PM. Can you suggest some fast growers for our 8 foot high fence? I was thinking of morning glories, but I don't know if they'd get enough sun in that location.

Thanks!

Adrian Higgins: Far too little sunlight for most flowering vines. Clematis might work. I would consider something for its foliage, bignonia or schizophragma, for example.

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Washington, D.C.: Good morning. I was given a bareroot rose for Christmas and left it outside on my porch until a couple of weeks ago, when I planted it in my front yard. I noticed that two of the four stalks (stems? branches?) are brown and, I suspect, dead. The other two are green and one now has a tiny bit of new growth on it. Did I kill my rose already? Or is it only mostly dead? Should I cut off the two brown branches? I really, really want this bush to live. Thanks very much.

Adrian Higgins: If there is some green growth, it lives. Cut out the dead canes and nurture it with good soil, occasional watering and a light feed.

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Silver Spring: Hi! I have a plot in a community garden and I know that the area is fairly well infected with tomato blight spores (problem in my plot as well as all of the adjacent plots)... however, I don't have anywhere else to plant tomatoes, so I have to come up with alternative management strategies. In past years, I've tried to remove infected leaves as soon as I see them, and I also put a straw mulch down... I was wondering if it would also be helpful to bring in some extra topsoil this year and mound plant my tomatoes using the new soil (I'm only going to put in a couple of plants). I don't know that I'll have enough new soil to encompass the entire root system, but I figured that it might be worth a try. Any thoughts?

Adrian Higgins: Yes, I think all those strategies would work. Make sure you pinch out the suckers in the leaf axils, to prevent the vine from becoming congested.

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Falls Church, Va.: I was interested to read in today's paper that last year's drought is not over in spite of our recent rainfall. I have several mature trees that got really stressed last year. One oak was attacked by borers and I had to take it down. Do you recommend any additional watering this spring for mature trees and foundation plantings?

Adrian Higgins: I think most of the damage has been done. That was a brutal drought. All you can do is give the trees a light mulch of compost, and keep them watered if and when it turns dry again this year.

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Arlington, Va.: Mr. Higgins,

Need a little help. My lawn looks abysmal. Weeds have overtaken what grass there is left. What steps can I take this Spring to save or start a new yard?

Thanks.

Adrian Higgins: You might try a little ryegrass to keep it going for a few weeks, but the main season of lawn renovation is in late summer, early fall. Unless you want to spring for sod, but that can be iffy going in to the summer.

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Alexandria, Va.: Last summer, my tulip tree (maybe magnolia) had a mushroom growing where the trunk meets the ground. I removed the mushroom in the fall. The mushroom has not grown back yet. The tree is otherwise healthy.

Is this tree dying? If so, what can I do to save it?

Adrian Higgins: The odd mushroom is OK. See if the wood is alive (scrape it to see if it is green). If your mushroom was bracket fungus on dying wood, that's not so good.

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Rockville, Md.: How shady is this? I have a north-facing slope I wish to plant with a ground cover. I think blue rug juniper would be cheap and attractive, but I'm concerned that it will find the north slope too shady. The area is otherwise un-shaded by trees or anything else. Are there better choices?

Adrian Higgins: You think of this as being a sun lover, though I've seen Japanese garden juniper growing happily in partial shade. I would consider some hellebores.

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Arlington, Va.: Good morning Professor! Last week, I asked you about some yellow flowers growing amidst daffodils between Rosslyn and the Pentagon. You said they might be Japanese Kerria, but the picture I googled didn't look right. I've now been told that they are actually flowering mustard greens - a weed! But what a beautiful weed. Do you know if this is invasive? Can I try to plant it?

Thanks!!

Adrian Higgins: It's rape seed, which is invasive. It's grown to make canola oil. It also attracts flea beetles, which isn't good for vegetable gardeners.

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Tomatoes: Adrian, I noted above your mention of mulching tomatoes "heavily" with straw. I also read this weekend on a bag of seed potatoes that we should mulch those with straw as well. I've never mulched tomatoes at all, and this is our first round try at potatoes. May I ask the purpose of the straw mulch? And is it to be placed all the way up to the base of the plant, or should we allow a radius between the plant base and the straw (how much). What about pepper plants?

This is a new idea for us, but we're open to trying it.

What happens to the straw at the end of the growing season? Does it need to be removed, or can it be tilled under?

We're in the Midwest, if it matters, so the tomatoes won't go in for another month until the soil is a bit warmer.

Thanks.

Adrian Higgins: The blight spores live on the surface of the soil. When it rains, the spores splash up on to the leaves of the tomato. If you put down a four inch layer of straw, you minimize that splashing effect. At season's end, you can pile the whole lot on to the compost pile.

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Woodbridge, Va. : Thank you for taking my question - love your chats! My roses are going gangbusters - but Saturday I discovered small wormlike insects on a few of the leaves. They were white - very narrow - about .5 to 1 inch long. What are they? Assuming they are not good, what do I do to get rid of them? Thank you!

Adrian Higgins: These might be inch worms, which are usually green. They can appear in large numbers and do a lot of damage. A Bt spray should work.

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Chestertown, Md.: Loved your article on the bayside vegetable gardens. If people would like to see the Van Dyke garden in person as well as other outstanding gardens in the same area, one also designed by Oehme and Van Sweden and some designed and maintained by the Mylander and Hollingsworth team, but all passionately cared for by the owners, they should check out the Maryland House and Garden Pilgrimage in Kent County on May 3rd.

washingtonpost.com: Maryland House and Garden Pilgrimage 2008

Adrian Higgins: Thanks for reminding me. Readers would love to see this property, I'm sure.

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Queenstown, Md.: We moved to the Eastern Shore a few years ago from southern Frederick County. It is a COMPLETELY different ecosystem! I have pansies, petunias, dianthus, etc. that never die over the winter and I am now in my 2nd or 3rd year of blooming with some of them. And all my herbs but basil survive in the relatively sheltered bed out front.

We have a southern exposure near the Wye River, so the water keeps it from getting very cold. My window boxes stay in bloom through Thanksgiving.

Adrian Higgins: Again, a response to the feature in Sunday's Magazine. Thanks for the insight.

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Bowie, Md.: Professor Higgins -

Thank you for the article on Chesapeake gardens. Now I know where I want to retire! I took advantage of the impending rain last weekend to lay down corn gluten on the lawn and in flower beds. Was I too late?

Adrian Higgins: Think that would be fine. I'm looking for a source of corn gluten.

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Fairfax, Va.: I'm moving into a new townhome this Summer and am excited to have my first backyard, with space for plants! The planting areas are completely bare right now. Can I plant anything in July when I move in, or am I better off waiting until next Spring? If I need to wait, I'll just spruce up the back with some potted plants until then. Thanks.

Adrian Higgins: You could brighten up the summer with annual in pots, and then work on a plan for planting in the fall. This is the best time to put in woody plants and hardy perennials. We're out of time, thanks for all your questions, and don't forget to see all the spring gardening coverage in Thursday's Home section.

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