Adrian Higgins gave advice on tending your garden in the summer

Jun 12, 2014

Washington Post gardening columnist Adrian Higgins took questions on how to improve your garden in the summer.

Why do my cucumbers get a mildew toward the end of the summer?

Hello, and welcome to our chat today. The heat has finally arrived, but things are still behind. And there's still time to stick in stuff for the long growing season ahead, including cucumber seeds! Cucumbers and other cucurbits naturally succumb to powdery mildew, usually the problem is late in their growing cycle, and thus not disastrous. You can minimize the problem by growing them on trellises, this improves the air circulation. This is not feasible for large fruiting melons and pumpkins, but perfectly good for cucumbers, smaller squash and zucchini. One of the most important ways of reducing this problem is to select varieties bred to be resistant. I am trying Fanfare cucumber this summer, and will report back on its performance. You can also spray preventatively with a baking soda solution.

My two wild rose bushes (Rosa carolina) are, well, wild. I've read that I should I just let them be, but would I do harm if I trimmed them back just a bit (or more than a bit)? And if I did prune them, could I do it in the summer, after they have lost their bloom, or do I need to wait until late winter?

These are once blooming species (I think) so they can be pruned hard after flowering. Wear long sleeved shirts and thick gloves! And yes, I've turned into your mother. 

How would I go about getting milkweed plants. I tried growing a few from seed, but they didn't sprout.

You can still purchase plants (too late for seeds, perhaps) of the perennial and annual members of the asclepias genus. I saw a section at Behnke's in the perennial dept. the other day, devoted to butterfly gardening and I believe they had some selections. 

I've been looking all over for this variety. Merrifield says it might be that there is no one out there growing it because no one seems to stock it. Any suggestions for where to look?

You might try some of the major growers such as Hines, Monrovia or Bailey's Nurseries.  

My landscaper advised that I sprinkle preen around my garden beds to control weeds. Your take on whether this is (1) bad for the other plants and (2) bad for the environment? I like to pluck by hand and I use a lot of mulch, but the weeds are really taking over!

Preen is a preemergent, so it won't stop those that have already germinated but will prevent further germination. They make an organic version from corn gluten. The downside is that if you have things you want to germinate, such as annuals and biennials, it would interfere with that. 

What ist he proper technique? My mother says to clip at the stem where it joins the main stem. I thought it was okay just to pluck the dead flower from its base.

You can either pinch the flower with your fingers, or cut back more with pruners, which will also promote bushiness.  

I live in the Intermountain West (Utah). I had 3 beautiful dwarf (maybe 3-4 ft.) ornamental peach trees (with flaming red narrow leaves) in huge pots in my yard. Over the past 6-7 years, they slowly but surely declined to the point where I had them jerked out and discarded. Sigh. A nursery guy told me that ornamental dwarfs in pots are doomed and to forget about replacing them. What do YOU think, garden master?

Any woody plant in a pot is going to be at a disadvantage, and when peaches become stressed by drought, they telegraph that to pests and diseases. I do though like to see a nice dwarf pomegranate in a large container. (Only to zone 7, if you're lucky). 

I have to thin my carrot seedlings. Are they edible?

The first thinnings won't be edible -- the carrot will not have formed. But successive thinnings will be. You want to keep thinning carrots until there is a good two inches or more between the mature ones. This is a laborious task but absolutely necessary for large carrots. When I seed carrots, I try to take extra time and care to space the seeds more than I would with, say, lettuce or beets. 

Quite a number of my plants have black spot so this cooler, wetter weather does have a down side. Any recommendations?

Depends on the plant, if it's a prized rose, it might make sense to spray but for a shade tree, it wouldn't. Some years are worse than others. It's sort of the same with sooty mold and galls. 

With all the snow and rain my lawn has become very patchy - whole chunks of bare earth and many areas of thin or weed only green. I know I should probably wait until fall to try seeding but is there anything I can do now to make it look less horrible?

Other than to keep the weeds mowed and to prevent them from going to seed, I wouldn't attempt any aesthetic revamp now. If you tackle lawn renovation in late August, it's going to take two weekends to prepare and amend the seed bed, and a month before that if you are applying herbicide to kill off everything. Arguably, fall lawn renovation is almost upon us. 

Too late to plant?

Forget the peas, but now is a great time to plant bush and pole beans, including limas and yard long beans.  And you can sow successively until the end of July. 

I have big time allergies to plants and grass and therefore, can't plant or upkeep anything myself. I have a friend who has volunteered to plant flowers and plants for me, but I need ideas for very low maintenance. I live on 1/4 acre with mostly grass and a couple of trees. Sunny backyard and shady (mostly) front yard. Can you recommend any books or online resources geared towards very low maintenance planting ideas? For instance, one thing that occurred to me was to get a shrub that grows only to about 3 ft tall and 3 ft wide, so it fits in an area that size, as opposed to a 10 ft tall shrub that needs continual trimming.

Not to be glib, but if a 10 foot high shrub is too big, don't plant a 10 foot high shrub, plant one that gets five to eight feet. My advice is to figure out the mature size of a shrub, find a spot with room and then wait for it to fill in, rather than to seek immediate coverage. There are many low maintenance but attractive shrubs that you could plant (and perennials), don't be driven just by flower ornament. Think about leaf colors and textures.    

I want to expand my use of ground covers to try to shade out some of the weed seeds which find their way into my garden. One bed is in full sun and despite amending the soil with permatill and compost still is primarily clay. Do you have any favorites to suggest ? Thank you. Always appreciate your insights.

I have used dwarf varieties of crape myrtle and abelia for such use. You could also try some deutzias. As for perennials, I would consider leadwort, st john's wort and and maybe some asters. 

For the past two years, my peonies have not been fragrant. They are old plants that have been divided many times. Could that be the reason?

There's no obvious reason for a previously scented peony to change its spots, as long as the bud is untroubled by wet or disease as the flower develops. Many blooms are fragrant at certain hours of the day, but not others. 

Does this work with a mulching mower or am I sowing seeds? My yard looks horribly weedy and patchy as well. Anything else we can do?

You don't want to let crabgrass, plantain, chickory, wiregrass  and other summer weeds to get to flowering stage.  But as I say, you can be preparing to renovate your lawn in a month from now. If you've lived with the weeds so far, another few weeks won't make a difference, especially if you are driven by the vision of a lush lawn come October. 

Here is a link to today's Local Living cover story, on creating a garden that doesn't attract bees.

We do these chats in association with my cover story in Local Living, which today is about dealing with bee stings as a gardener. Anyway, here's the story. (I did get an email from a beekeeper thanking me for pointing out the difference between a honeybee and a yellow jacket).  

I’m looking for a plant/shrub/tree for the front corner of my house between the driveway and the front walkway. The front door is in the center of the house and I have 3 boxwoods on each side. The place I’m looking to put the plant/shrub/tree is to the right of the front door and boxwoods, where an oversized hemlock out grew its space. The space gets a half a day of sun starting in the afternoon. Any ideas? Thanks!!

There are some magnificent dogwood hybrids that have been developed of late. If you have the space, I think this is a tree that has fallen from grace in recent years because of the anthracnose problem and worthy of more attention. 

I'm trying to grow bell peppers in a planter for the first time. Actually, it's my first time trying to grow bell peppers! It's in a very sunny, eastern-facing location. The plants are about 8" tall and now have yellow spots. Is this a virus, too much sun, or (hopefully) nothing to worry about?

Peppers can suffer the same blights as tomatoes, but it may just be stress associated with planting in early season, or from too much moisture in the soil. Do make sure your planter is draining well. 

Adrian - A couple of chats ago, I asked you to keep us updated via twitter about what you're doing in your garden so we could know the proper timing of things (at the time it was starting onion and leek seeds). Well?!?! Where are the updates?!!?!? I just started a batch of fall and winter leeks last night. When do you start fall broccoli? Thanks! And thanks in advance for all the upcoming twitter messages!!

OK. I can tell you what I'm doing at the moment: Finally harvesting my fava beans. When they finish, I will put in parsnip starts. I have just about finished (late) installing peppers and tomatoes, and have pulled all the lettuce to make way for them. I'm waiting for stuff that's already in to do its thing so I can harvest it, that includes potatoes, broccoli, cabbages and spring onions. 

Hi, I have a gravel driveway and the weeds are impossible to control. I usually pull them by hand and then use the weed whacker, but it is arduous. I don't use pesticides anywhere for a host of reasons, including that I live very close to the Bay. It seems even organic pesticides can be problematic. Do you have any suggestions? I'd be willing to consider a product that wasn't harmful to the environment, if there is such a thing. Thanks!

I simple use a sharp hoe in my gravel beds, it works a treat. I may rake it smooth afterward, depending on how carried away I get. 

Our back neighbors have offered to plant a privacy hedge of green giant arborvitae in our yard. I worry that they will require lots of maintenance, seeing as they grow to 50-60 ft. We have a tiny, East-facing yard, and although I'd like the privacy, I'm worried that our house will get very dark year round. I know you have opinions on screening evergreens. What would you suggest? Thanks for taking my question.

Green Giant is the default evergreen now that people have realized that Leyland cypress is a monster. It will take a long time to grow to that height, though. It's hard for me sitting at my desk to tell you what size of hedge you might need. I might consider Chindo viburnum, osmanthus or some holly. If it faces east, you will still get afternoon sun, but it will darken your house in the morning. 

Hello, thanks for taking questions. I have an abundance of thoroughly composted horse manure and bedding, and the supply is always being renewed. : - ) Can the composted material be used as topsoil? The soil level around the house foundation needs to be built up, but I want the soil to support some new landscaping.

Horse manure with straw bedding is better than with wood chips, but both accelerate the composting process. I would just watch for surviving weed seeds. Rotted compost is not soil, it is used to mix with soil to provide organic matter. It has relatively little nutrient but is loaded with microbes that feed soil life and radically improve the structure of your soil. However, garden beds right next to the house should not be too open in structure because storm water will find its way into your basement. Better to have denser clay there. Keep unrotted manure out of your veggie garden. I'd a wait a year before incorporating that into your edible plant beds for safety reasons. 

In the DC area you can plant peas in late July for a fall crop.

It's a gamble. They might work but you have to run the gauntlet of too much heat first and then cool temps at fruiting time. I would try one sowing in late July and another in mid August. 

Thanks so much for your article on this winter's hydrangea setback - I thought I was the only one who got slammed. I cut the dead parts back hard - will the plant likely fully regenerate or will it come back smaller?

It will come back fully, it may take two seasons to attain its mature height. The roots are large and established, so regrowth will be vigorous. A little feed may help. 

We have a pair of overgrown, unsightly evergreen shrubs on either side of our front path, making our small front yard seem even smaller. I would dearly love to remove them and replace them with something prettier. What would you recommend as a hardy, low-maintenance, replacement? One side is in full sun and the other is shaded by a dogwood. Is there any particular time of year best for removing them?

I would go to a public garden (National Arboretum, Brookside, etc.) and see what you like and its size, location etc. You could take out your ugly shrubs now at your own pace, and then have the beds ready to go in September. Fall planting is best for most shrubs because the plant isn't putting energy into new growth and is developing roots for the following season. I see the clock has beaten us here again. Will see you soon. Break out those Hawaiian shirts. Luxuriate in the tropical heat of the DC summer. 

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Adrian Higgins
Adrian Higgins is The Washington Post's gardening columnist. Read his recent story on reinventing the winter-weary hydrangea and follow him on Twitter.
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