The Garden Plot: Lawn Aeration, Hydrangea Colors, Poison Ivy, Horticulture Careers and more

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, September 9 to offer advice on 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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Alexandria, VA: Hi Adrian. I have a dry shade area that needs some smaller sized perennials. I already have hostas and coral bells and I'd like your advice for some other colorful additions. Thank you, as always, for your suggestions!

Adrian Higgins: Morning everyone, hope the storm didn't batter everything down for you too much. We needed the rain, pity it didn't come in more gradual amounts through August. Coral bells will do all right in the dry shade, hostas may need a drink now and again. I love epimediums, of which there are many varieties these days. And well worth seeking out.

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Columbia, MD: Submitting early...

From my home office window, I have a view of land that is approx. 9'x9'. Currently, it looks messy with brush. The area does get a lot of sun. I would like to clear the area. I love tall grass. Would that be a good choice for the area with also a hydrangea? Do you have any suggestions for the area?

Thanks.

Adrian Higgins: Most grasses like full sun and somewhat dry soil, hydrangeas like afternoon shade and evenly moist soil, so the two don't make good bedfellows. Some of my favorite tall grasses are miscanthus November Sunset and any of the panicums.

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Silver Spring: Hi Mr. Higgins,

Would now be a good time to aerate and re-seed one's lawn?

Adrian Higgins: It would indeed. If you are a man (or woman) enough to lug the machine. I like to lay compost over the lawn before aerating so that when the machine removes the plugs, the compost automatically fills the holes. You will then have the essential seed to soil contact that you will need. Aerating also dries out the roots of the remaining turf so it's important to keep the lawn well watered afterward. Mid Sept to mid Oct is the optimum time for sowing cool season grasses in our region.

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DC: Realistically, how long should I wait for a phaleonopsis to rebloom? I cut it back once all the previous blooms fell off, almost 5 MONTHS ago! New leaves have sprouted at the base, looking very healthy, but no movement at all on the stem. When do I give up on it?

Adrian Higgins: You shouldn't give up, as long as the leaves are growing and healthy there's every chance that the orchid will produce a new flower spike. I have a friend who waters her moth orchid twice a week (in very free draining orchid mix) and it blooms all the time. Go easy on the fertilizer, though.

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Potomac, MD: What can I plant under my dogwood (besides grass) that won't hurt the tree?

Adrian Higgins: Grass, incidentally, is about the worst thing you can have under a tree. The watering and feeding requirements are quite different and if you use any sort of fungicide, there's a good chance of killing the beneficial microbes that the tree roots need. I would clear away the turf, being careful to minimize root damage, and create a bed with two to three inches of screen rotted compost on top. You could then plant a host of small ground covers, including native gingers, foam flowers and specialty bulbs such as snowdrops and glory of the snow.

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Falls Church, VA: I have a recently planted Kousa dogwood in my front yard that doesn't seem to be thriving. The edges of the leaves are turning brown, and a few are starting to turn yellow and red. I keep checking the soil and the moisture level appears fine, but should I be concerned? Thanks!

Adrian Higgins: Perhaps. Most young trees are actually killed by well meaning owners who water them far too much. I don't know what your watering regime has been, but in addition to giving it a really good soaking when first planted, I would not apply more than five gallons per week, and in one go. Again, a light mulch of organic material, kept away from the trunk, will temper soil moisture and temperatures. The acid test will be next spring.

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Washington, DC: If it seems like overkill to rent an aerator, i.e. if you have a small city lawn and strong legs, there are also manual core aerators that you can buy for under $20 that do a fine job. You step on the cross bar to plunge it in and extract the plugs.

Adrian Higgins: I couldn't agree more. The machine one rents needs two strong people just to unload, assuming you have a pickup truck. I wouldn't recommend renting one unless you had at least 5,000 sq ft of lawn. The one thing that isn't much use is the spikey aerator, which does little to open up the soil and actually causes more compaction, which is what you're trying to undo.

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Philadelphia, PA: Hi Adrian, when is the right time to move my Asiatic Lily? The leaves and stem starts browning now. How do I move them? Thank you for doing this chat, I've started knowing my way around my garden.

Adrian Higgins: Now would be a good time. You could cut off the top growth and bury the bulb in rich soil, and to about seven inches, or more. It will produce new roots and scales over the fall, and flower robustly for you next summer. Lilies like their feet in the shade and their head in the sun.

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Rockville, MD: Hi,

I moved into a home with existing lavender bushes and would appreciate some tips for caring for them. I read I shouldn't prune the brown branches?

Adrian Higgins: Lavender should not be treated like a perennial and hacked back hard in late winter. You should wait until you see new growth in the spring, and then trim or remove errant stems.

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Hartfield VA: European hornets are stripping the bark off the branches of my heritage birch trees. Will this cause permanent harm? What control options are available?

Adrian Higgins: They can kill lilacs when they do this, because they girdle branches. Since birches naturally peel, perhaps the damage will not be as severe. Not much you can do about this, I'm afraid.

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Capitol Hill: The city graciously planted a tree on a barren strip of soil next to the sidewalk by our corner house back in April of this year. It looks in rough shape, some twigs, some brown leaves, all mixed in with some green leaves and what appear to be new green growth at some branch tips. I've watered well during dry times, but is there anything I can do to improve its chances of survival and robust health overall??

Adrian Higgins: I would prune out any dead branches now, and make sure the base of the tree is not afflicted with a mulch volcano.

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Falls Church, VA: Hi Adrian. Our backyard is almost completely dirt. Compacted, hard as a rock, won't grow even weeds, full of tree roots from 21 trees, and doesn't absorb rainfall at all. I'm thinking that aerating would go a ways towards reducing the compaction and hopefully stop rainfall from washing right off the surface and down to our house's foundation. Long term I'd love to be able to put some sort of plants in, but the existing soil is impossible. Is aerating the way to start this project? Do you have any other thoughts?

Adrian Higgins: Aerating may reduce the compaction but would damage the roots. There is another technique called vertical mulching, in which you take an auger to the soil, not the roots, and backfill the hole with organic matter or even gravel. I would consider removing some of your trees.

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McLean, VA: Hi Adrian, my wife and I planted a few hydrangeas this spring and summer and one in particular was given to us by a friend when they split a very large (5ft.) plant into thirds. Much of it has browned out, but there is one large branch that is still holding green. What, if any, pruning should we do to give it a better shot at thickening out for next year's growth? I'm a novice when it comes to flowering plants. Thanks.

Adrian Higgins: Hydrangeas thicken by producing suckers from their crown, so while you could induce branching by trimming this one stem, you will also lose flowering wood at this stage. So I would say, don't prune, just keep it mulched and watered, and be patient.

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New York City: Do you have any recommendations for someone who wants to switch careers and get into horticulture? I'm currently getting my certificate in horticulture, and was wondering what the logical next step would be - whether it's more education or where to get my foot in the door job wise.

Thank you.

Adrian Higgins: You have a lot of options, either at public gardens or nurseries, of which New York and environs has many. If you email me, I will put you in touch with some people at the New York Botanical Garden who may be able to advise. higginsa@washpost.com.

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Washington: I tried growing broccoli this year, but it didn't quite work out. I saw something that looked like what you eat, but it was mostly long spindly things jutting out. It's still like that. Was there something I was supposed to do?

Adrian Higgins: Broccoli is best grown as a fall crop here, but unless you can find plants, it's a bit late for them. It is best to install seedlings in August.

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DC: What is the best way to store spring bulbs between buying them and planting them? I usually wait for the weather to cool off but want to buy the freshest bulbs I can find. Thank you.

Adrian Higgins: Great question. I store mine in a spare refrigerator, but not the freezer. Daffodils can go in soon, but tulips should wait a month.

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Batesville, Va.: We have just sown a cover crop of crimson clover in our upper vegetable garden. We hope to realize the benefits (nitrogen-fixing, etc.), but will the clover attract more deer than usual to the garden?

Thank you for your forum and for your weekly column!

Adrian Higgins: Possibly, but it is such a beautiful and useful ground cover and green manure that I would take my chances. I have sown it in the fall and watched it bloom in late winter.

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Southern Maryland: I have a butterfly bush in my backyard, right outside my kitchen window, that is/was frequently covered with monarch and swallowtail tiger butterflies. It also attracts hummingbirds and is my entertainment center during the summer. During an earlier storm this summer a big limb from a cherry tree fell on the bush and broke several branches. The tree trimmer cut back what he could but now it looks very straggly. How far back can you cut a butterfly bush and still have it survive? Is it possible to kill those things?

Adrian Higgins: If a branch is broken or dead, yes, take it out now. Otherwise, and for the rest of the growing season, I would trim it back to encourage a final flush of blooms in late October. In late winter, you can cut it back to 12 inches, and it will resprout merrily. Hard to kill those puppies.

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Reston: Re: laying compost over the lawn before aerating.

Wouldn't this defeat the purpose of aerating? I thought air was supposed to fill the holes. The compost doesn't get in the way?

Adrian Higgins: If you are simply aerating, you don't need the compost but if you're are seeding at the same time, you don't want the seed to fall into those holes. The compost is much more open than the clay plugs that are removed, so you are still achieving the de-compaction (new word?) you want. Do not top dress with topsoil, however, because that would defeat the purpose.

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Washington, DC: I planted a fall zuke crop on Aug. 1 and got flowers starting just before Labor Day. So far, all of the flowers appear to be male flowers. What should I do? thanks.

Adrian Higgins: Wait. Though you may be hard pressed to get fruit before everything cools.

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Washington: I'm taking a botany class now and the professor was saying how she couldn't find any scientific information on exactly what makes hydrangeas change color. She says people seem to only know how to make them change color, but not why or what the chemical process is. Do you have any info that would make me look good in class? Thanks

Adrian Higgins: It's the availability of aluminum ions in the soil. There must be some detailed botanical explanation on the Web, somewhere.

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Washington, DC: This was my first year with tomatoes (in containers) and it was pretty successful, some varieties more than others. Now that they are almost done, I was wondering if it's okay to put the vines and the container soil in my compost bin given that I had some blossom end rot and some kind of problem with wilting (fusarium?).

Thanks for the chats--they are so informative!

Adrian Higgins: If you've had fusarium wilt, bag that stuff, don't use it in the compost.

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Arlington, VA: The previous owners of my house allowed poison ivy to grow up a tree and reach its mature, branch-like form. Fall is approaching, so I'd like to ask, How do I kill it without harming the tree? Should I slice through the vine (and into the tree) and hope that's enough to kill it, or should I slice halfway through the vine and apply an herbicide to the cut (and hope the herbicide doesn't get drawn into the tree)?

Adrian Higgins: First, make sure you are well protected and don't burn the vine, the fumes will cause rashes. Cut the stem and apply glyphosate with a paint brush to both cuts. Repeat once or twice in a week. You may have to wait several months for the vine to be dry enough to rip out of the tree, which won't be harmed by the glyphosate if you keep the application to the vine. This will also work for English ivy.

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Rockville, MD: I'm confused - how does top-dressing with topsoil defeat the purpose of aerating?

Adrian Higgins: Because top soil is not a regulated product and you may be getting clay that has been fluffed up in a grinder with mulch, but will set hard at the first rain.

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Arlington VA: I bought Sweet William at the Cathedral's Flower Mart last year, planted them and they were very pretty. I left them throughout the winter with no attention, and starting in May of this year they were absolutely beautiful. They have even been blooming again in the last couple of weeks.

Will they bloom again next year? If there is a chance, I want them to survive, but I understand some biennials don't.

Adrian Higgins: Sweet William, as you say, is a biennial. You should put in a fresh plant now for display next year. Or start them from seed in the spring.

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Moving plants...: Hello Oh grand gardener.. I am remodeling our garden and seem to move more plants than not. When and how do I move a Hydrangea? It's a 5 year old plant, and went gangbusters this year... but it's in the wrong bed! Also moving an old BLAZE climbing rose... and small nandinas. Any and all comments muchly appreciated!

Thanks muchly, your monthly "what's in bloom and what to do task list" is a pure blessing!

Adrian Higgins: Thanks for those kind words. Now is the season for moving plants, the hydrangeas and nandina should move easily, but an established rose may not survive, the roots go deep.

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Washington D.C.: Hi Adrian!

I live on the second floor of an apartment building on the North-facing side and I don't have a particularly green thumb to begin with. Is there anything I could grow in a windowbox (if possible, I would prefer herbs/lettuces/veggies/fruit, but any greenery at all would be nice) or should I just leave the balcony to the charcoal grill?

Thanks so much!!

Adrian Higgins: Make sure the container drains, and is full of fresh, organically rich soil and sow some lettuce seeds this weekend. Thin the seedlings, first to two inches apart, then four and finally six. You can eat the thinnings. Get more containers and repeat, perhaps with arugula and spinach.

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Manassas, VA: I saw a beautiful Lantana shrub in VA Beach last month. I would love to plant one in my sunny backyard. I did a search online and found out that the Son cultivars are cold hardy. Have you had or seen any in our area? And if so, do you know where I can purchase a larger plant? The ones I have seen are in 2" pots.

Adrian Higgins: I am told that the variety named Miss Huff is hardy in a protected site.

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Rockville, Md: Our mature stewartia has suffered significant die back the past couple of years. It seemed to begin with the blossoms not completely opening and progressed to the branches dying. Have watered during summer droughts and into the fall for the winter. New growth from the established trunks is sprouting. Any suggestions? Thank you.

Adrian Higgins: Stewartias like even moisture and cool soil, again you have to walk that fine line between avoiding drought conditions and not overwatering them. I would apply a thin mulch of compost and also give the tree a feed with liquid kelp and fish emulsion. Cut out any dead branches now and again after bud break in the spring.

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Aeration: Good tip on the laying of a layer of compost post-aeration and pre-seeding. Thanks. Fall lawncare is one of my favorite gardening tasks because it's so renovating and rewarding. And it can be fun. I'm renting a core aerator this weekend. What I do is lure a couple neighbors into doing it with me. We all split the cost, help each other haul it around, and it ends up being cheap and (fairly) painless. I don't have a big lawn at all, but doing this each year, I think, has a big impact on the quality of my lawn. Also, you don't really need a pickup. It fits into my Volvo station wagon. (By a hair).

Adrian Higgins: Hooray for Volvos. Great idea, sharing with the neighbors.

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Johnstown, PA: While visiting the DC area, my parents were very impressed with the variety of crape myrtles and would like to grow some of their own. The problem is that they live in the middle of Pennsylvania and appear to be just out of the recommended range for crape myrtles. Are there any hardy varieties that might do well for them? thanks

Adrian Higgins: Haven't you heard of global warming? I would check with the Brooklyn Botanic Garden to see which varieties they grow. Their zone might be a little milder than Johnstown, but not by much I would think.

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Richmond, Va: What are some good tree selections for street trees that will be growing under power lines? Neighborhood has some empty tree wells and is already populated with Natchez crepe myrtles and forest pansy redbuds - we might like some more variety.

Adrian Higgins: Thank you. Enough of Natchez, people. I would consider European hornbeam or even something whacky like a pomegranate or Asian persimmon (though the fruit might be messy).

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I'm a KILLER: I keep killing my basil and rosemary. they are in small pots on my balcony. Direct sun from 3 until sunset. Only water when necessary (very scientific finger inserted into dirt measurement method). What am I doing wrong???

Adrian Higgins: We're all killers, that's how we learn. (Sounds like a script from a Sly Stallone film) Basil will only be good for another month. I think small pots are a problem for both these plants, I would put them in larger pots so the soil moisture doesn't fluctuate quite as much. The finger in the dirt method is the best, by the way.

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Takoma Park, MD: Sneaking this one in! Any advice for a tall skinny office plant? I have a west facing window and all the fluorescents a plant could need! I have a pretty green thumb, so I'm not too worried about killing a difficult plant.

Adrian Higgins: What about a Kentia palm or something as boring as a philodendron? Lame, I know.

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Native Californian: Many years ago my grandmother decided to clear some rural brush (which contained poison oak) by burning. The inhaled smoke from it landed her in the hospital very ill, due to the poison oak. The only consolation was that for the rest of her life she was immune to poison oak, but I doubt it was worth the suffering.

The Lantana that Californians grow is a very invasive plant, so I'd advise no one to plant it unless they want it there forever, and spreading.

Adrian Higgins: Both points worth noting. Lantana is also a problem in Florida.

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Silver Spring: Hi, besides my lawncare reseeding and aeration rigamarole, I was also going to sow some larkspur, nigella, California poppies this weekend... maybe some bachelor buttons and flax. Is this an OK time to do all that, or should I wait til later in the fall? Same for bulbs like allium? Daffs? Tulips and scilla?

Adrian Higgins: I would sow those now, and then give them a light covering of soil or screened compost. When you rake leaves in Oct. and Nov. be careful not to disturb the seeds and emerging seedlings. We're outta time, folks. Thanks so much for your questions. Tackle those lawns!

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Anonymous: re: your monthly "what's in bloom and what to do task list" is a pure blessing!

Can you provide a link for this? Thank you

washingtonpost.com: Fall Blooming Calendar

Gardening Calendar

Adrian Higgins: One last one...

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