Adrian Higgins on gardening

Courtesy of Rutgers University
Sep 14, 2017

Washington Post gardening columnist Adrian Higgins took questions on gardening.

What's your favorite dwarf crape myrtle for this area?

Greetings, all. This week I wrote about mulch, trying to get a handle on why we use quite so much of it. Not sure I know the answer. Anyway, the National Arboretum has been a leader in the release of mildew resistant crape myrtles. This is a truly dwarf introduction, named Pocomoke.

I planted a cherry red cultivar about eight years ago (can't remember the name) and it has grown to about three feet high and four feet across, bigger than anticipated. They can be trimmed back or even treated as a perennial, by cutting them back hard in winter -- but only after they are established.  

Here is a link to Adrian's most recent column, on how Americans love--and misuse--mulch.

I'm a big fan of raised beds. Can you suggest any long and shallow boxes? I also want to protect them from an over-zealous lawn crew who weed whack any hint of grass. I told them about my black-eyed susans this year, but they don't pay attention.

I create raised beds in my vegetable garden by taking planks that are eight foot by six or eight inches, and then position them by hammering in lengths of rebar on each side. I use a level to make sure the plank is level. Sometimes you need four sections of wood to create an open box, or sometimes you just need one, depending on the topography. If I can find cedar I use that, but otherwise use untreated construction pine and just plan on replacing it every three years or so. If you are just growing annuals, you could use a pressure treated plank. Backfill with enriched soil, and you're ready to sow your sunflower seeds in May. If you are bothered by animals, you may want to start them in pots first before planting out. Sounds like a fun project. 

Hi, I've got a pink dogwood in a pretty sizeable front yard bed and would like to plant ground cover underneath. I've tried candytuft, which kind of struggles along and never really thrives. Any other suggestions?

Ahem, you need to read my piece on sedges, the perfect ground cover for shade.

I have three red twig dogwoods ("cream cracker") along the foundation of the front of my house under a large window. They were planted three years ago and looked great this spring. Now they don't look well and have black on stems and leaves. From googling, I gather this is a fungus. If this is the case, are they salvageable? If not, what would you recommend replacing them with? I have always thought they were planted too close to the house and too crowded. Thanks for any advice

If I lived in, say, rural Vermont or Scotland, I would plant oodles of redtwig dogwood, especially on wet land. A massing can look spectacular in winter, when the twigs glow brightly. They underperform in hot, humid climates, their heart doesn't seem to be in it. They can look ok with proper care, which includes giving them space, ample moisture and an annual regime of rejuvenative pruning, but otherwise they're a bit of a let down. They suffer from a canker disease when stressed. You could try to revive them by cutting out the diseased stems, giving them some watering (but not feeding at this point in the year) and a nice mulch of leaf mold, and then remove all the oldest canes next March. If you wanted to cut your losses and plant something else, I do like oakleaf hydrangea as a shrub about the same size but with lots more seasonal interest. 

Regarding mulching trees, particularly young ones, some landscapers define the mulch volcano or mulch ring further by cutting a trench four to six inches deep into the ground around the outside of the ring. Isn't this an unhealthy practice? Kevin Sherlock, Alexandria

I' m not familiar with this, this sounds like a form of root pruning that you would do in advance of moving an established tree or shrub. When you plant a tree, it is important to remove anything at the top of the rootball that might constrict future growth. This includes tied burlap and the top parts of any wire cages. Any sort of nylon cord needs to be removed as well. You should not heavily amend the soil, so that the roots are encouraged to move into the surrounding earth. But you should break up and loosen the soil in a 12 inch ring around the rootball so that the young roots are encouraged to move outward . Maybe that's what you're seeing. It's also important to give a new planted tree a good soaking so that the water can chase away any air pockets around the roots.    

Mr. Higgins, Is there a showy perennial or flowering shrub for damp shade that I can put in with a river birch this autumn? I've planted a lot of natives recently, so feel free to splurge without that constraint here. Thanks!

To me, birch groves cry out for something a little restrained, perhaps with some ferns or, again, sedges (there are many that will take damp conditions). One quirky thing that might do the trick is the hardy begonia, which spreads when happy in damp areas, and forms colonies of late season perennials. You could add some Japanese or Siberian irises for spring display. 

Large area of stiltgrass (2,000 sq ft) growing in shade due to heavy tree canopy. Would like to remove and start grass seed, and open up sun exposure to 5-6 hours and dappled shade, thereby offsetting some of the existing shade. This would be a big job; if homeowner plans to tackle this himself, is this better done in "bite sized" pieces over a few years, or all at once? As for means of eradicating the stiltgrass, do you recommend raking it out or hand-pulling? Or is there an acceptable alternative?

If I had that large an area of stiltgrass I would seriously consider an herbicide. But do it soon because it's going to seed. If you are seeding in grasses, I would then smother the dead stiltgrass with a generous layer of weed free compost and seed into that. If you are planting plugs, I would not disturb the soil and plant through the dead stiltgrass. Both methods will minimize soil disturbance and the germination of latent seeds, of which you probably have a lot. 

I used to joke that when I retired, I would become a mulch vigilante, sneaking around at night with a rake and shovel, destroying mulch volcanoes. (Unfortunately I'm getting too creaky for activism.) I even drive 40 minutes to a place that sells pine fines, upon your recommendation. Now: can you tell me why my cardinal climber and cypress vine didn't bloom until just a couple of weeks ago, and very very sparsely? They've been reliable vines for the past several years but this past summer they were duds. Lots of vine & leaf but almost no flowers.

You should have a license plate with "Vesuvius" on it. Both these annual vines are related to the moonflower and like that big beauty, bloom late in the season, so don't give up on them yet. I suspect they set buds based on shorter day lengths. But the more sunlight, the more blooms. 

I admit I lost control of the weeds this summer. Is now the time to clean up? And what I can I do now to set myself up for success next year?

Sorry to be a scold, but weeding the garden isn't a once or twice a year event, it's the quintessence of garden maintenance. Only by regular weeding will you get on top of the weeds and tackle them on your terms, rather than theirs, i.e. a depressing days-long assault. 

The city was kind enough to expand a tree well in front of my house. However, it's not like they planted anything or even put in good soil. Now it is a mass of weeds. What can I do to make this area remotely plantable next Spring? Can I put down newspaper/cardboard and mulch and hope it kills all the weeds over the winter? Looking for a quick and easy solution this Fall and will allocate more time next Spring. Thank you.

This sort of follows on from the last question. The first thing I would do is pull the weeds and then put down a thick mulch. Layers of newspaper and cardboard will help block the weeds and weed seeds already in the soil, but not the weed seeds that will continue to arrive and germinate in your bed. These may include winter annuals that if you left them untended until next spring would become a right jungle. I'm not sure if this is a tree box where you plan to put a tree, or if you are just planning on a ground cover, or both. Could you not plant it this fall? 

I'm in Howard County MD and I planted a supposedly hardy fuchsia that died the first winter. Is hardy begonia equally uncertain?

No, fuchsias here are a passing fancy, but hardy begonia is quite dependable. 

Our small back yard (the property was split before we bought our house, and two houses built behind it) has deep shade from red and Norway maples, and the grass is now pretty much all stilt grass. I'd like to replace it with sedge, but I see your article mentions separate types for deep shade and for wet soil. Our back yard is pretty wet most of the time; do you recommend a particular sedge for such a situation?

This is the section on sedges for wet areas: In difficult wet areas, the options include the palm sedge, Gray’s sedge, Cherokee sedge, Bowles’s golden sedge and tussock sedge.

I would also consider taking down the Norway maple, which is dense in leaf and dense in root -- unfriendly to other plants as well as invasive in some states. 

I'm emailing you a photo of the space created when I cut down a twenty-plus for tall weeping cherry (it was sickly.) Our backyard is filled with nothing but trees, shrubs and perennials and the small brick patio. The dominant tree in the yard is a 15 foot crepe myrtle that we expect to fill in more on the side that it shared with the cherry. We're looking for suggestions to replace the old tree. Bringing a stump grinder in is not an option and using a chemical approach to remove is not an option for 12-18 months (if at all.) Thanks. JY

Here's something to consider. If you take down a tree, you don't have to replace it with another tree, you could opt for shrubs and perennials and ground covers. I would consider that, especially if you have a mess of trees on your lot. 

I have noticed that we have gotten too many slugs this year which has killed many a perennial. How do i control them? We put down newspaper then mulch around our plants. Would this be our problem? Thanks.

It's been a fairly wet summer, and the slugs are happy. You can use organic slug killer, but I'd be leery of that in and around any sort of edible plants. Beer traps are effective, if you police them. You can also go out at night with a flashlight and put them in a pail of bleach solution, but use gloves. The slime is pretty awful and persistent. 

Hello Adrian! I have three of the unappealing trees. I want to replace them, preferably with something that provides good bird habitat without growing too wide. Have any good options for me?

I might try something more shrubby, which will give birds a place to roost and get away from predators. Is Burford holly too trite? You could try Yaupon or American hollies, or larger forms of falsecypress. 

we have a beautiful one as a foundation planting but it's overtaking the yard. When, how, and how far to cut it back?

They don't lend themselves to easy pruning. If they are too large, you can remove whole stems, but do it without disfiguring the shrub. Removing them now may lose you blooms next year. 

What can I plant now? I'm itching to put something in the ground. I have a 5-by-10 planter that's a blank slate.

My general advice is don't plant a big tree or shrub that in five years you will be constantly chopping back. Nor would I plant a lot of fussy things. I would pick three varieties of perennials and perhaps a small shrub, and do some massed plantings that will look handsome and calm. Alas, we have run out of time, but have fun in the garden now that the weather beckons us outside. 

In This Chat
Adrian Higgins
Adrian Higgins is The Washington Post's gardening columnist. Read his latest columns and stories here and follow him on Twitter.
Kendra Nichols
Recent Chats
  • Next: