Adrian Higgins gave advice on tending your garden in the fall

Sep 12, 2013

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

I will be starting a new raised garden in the spring. Should I build and fill the garden beds now and cover them until planting in the spring or should I wait until just before planting?

Hello everyone, and thanks for joining us for the next hour. In today's paper we wrote about the plight of butterflies (monarchs in particular) and honeybees and bumbleebees, and the ways that everyone can help them. Thanks for this question: I can't tell you how many times people suddenly wake up to gardening in March, when it is too late to attend to the structure of a garden. This farsightedness is commendable. It means, first of all, that you can take your time to get it right, that you don't have to rush yourself and get stressed about it. The first thing to consider is if your planned beds are wide enough. A common mistake is to make them too narrow. Think about that. By giving yourself time, you can back fill the bed with your native soil mixed liberally with organic matter, then I would cover it with landscape fabric to keep weeds away and to encourage earthworm activity. You can spend the winter compiling a plant list. You will then find that by March it has settled a little, giving you an opportunity in early spring to add more good stuff to the bed. 

Here is a link to my story about creating a garden to attract pollinators, from the cover of today's Local Living section.

when is the best month to do fall pruning. I live in southern oregon.

There is one school of thought that there is no bad time to prune, in that simply getting to the job is the most important thing. However, there is another belief that pruning now as woody plants prepare for winter dormancy that you will encourage fresh growth that will be prone to frost damage in November. It also depends how you prune. If you remove and entire branch, that is going to have less of a regrowth effect than trimming back to existing foliage. The best time to prune is in winter dormancy, or in the case of hedges, after the first flush of spring growth, in June where we are. 

Like many others at a community garden here in Minnesota I lost all my garlic last spring to what appears to have been Asters yellow disease. Can I plant garlic in the same plot this fall, or will the disease still be a problem? Jim A.

Allium rots persist in the soil, I would find another place to grow it.

I've heard a lot about planting clover and other "green manures" over winter, then turning them into the soil before spring. Does it work if you just toss handfuls of clover onto the soil and tilling it into the soil in late fall? Or are those rootlets the things that are important?

Winter covers are great for beds that otherwise would be fallow for the cold months. Importantly, they prevent the soil from being overrun with winter weeds. Legumes such as clover have the added value of adding nitrogen to the soil, but winter oats and wheat are great as well. Vetch tends to reseed and come back in a way that isn't always desirable. I like red clover, simply because it is beautiful. Cut it down in late winter, dig it into the soil, and you're ready to go in the spring with veggies and/or new ornamentals. 

I need a few ideas for a variety of small evergreen and/or flowering (non-white) perennial plants around the mulched area where my mailbox is located. What do you suggest? The area is about 2'x3'. I want to keep it small/miniature.

I'm a big fan of the underused Deutzia 'Nikko', though the blooms are white. (In May, you could go on vacation to avoid them). 

Thank you for your informative article on planting for pollinators in today's Local Living section. The cover art is spectacular! Loudoun Wildlife Conservancy started a Monarch Campaign this year. Commuters probably noticed the LWC Monarch Campaign banner on the Dulles Greenway last summer. LWC's website at is just chock full of useful information about helping the Monarch Butterfly locally. LWC is hosting a native plant sale this Saturday, September 14, at Rust Nature Sanctuary in Leesburg. Local nurseries will be onsite selling native plants appropriate for pollinator gardens. There will be displays about planting Monarch Waystations. Experts will be onsite to answer questions. And best of all, LWC will be selling milkweed plugs from Monarch Watch and might even have Monarch Butterflies to release! Plus, they'll be selling their popular and beautiful Monarch Campaign T-shirt, their Field Guide to the Butterflies of Loudoun County, and signed copies of "How to Raise Monarch Butterflies"!

Fantastic. Thank you and passing along. Get out there folks!

Your article on pollinators comes at a propitious time. I recently had a loved but dying dogwood removed and it has opened up a sunny patch in front of the house for replanting, I currently plan to put nandinas against the foundation, but would love to see more butterflies. We already have a clethra and some buddelias that are a butterfly and bee party zone in July and August. Are any shrubs good fits (and deer resistant!)?

I can't vouch for the deer bit, but caryopteris is now in bloom and smothered in pollinators. Early and late season flowers are really important for the bees. Do deer eat asters? Asters would be fantastic. Deer won't eat lavender, which can bloom twice in a season, and for long periods. Mountain mint is a spreading native perennial, but it functions as a small shrub ground cover and deer dislike it, I'm told. (My critters run to chipmunks, squirrels and a neighbor's cat that kills birds in my garden). 

Good morning - I have a garden plot I rent from Fairfax County and this year my wife wanted to do a fall garden. We spent the last two weekends getting everything ready for the changeover but as we hit mid-September, we wonder if we got started too late and want to know what we can reasonably plant at this date and still have some yield before winter. We have seeds for carrots, radishes, kale, broccoli, spinach and arugula and we want to do garlic later (6 weeks?). Thanks.

All these will work, the carrots may be small but you can get them through the winter with a little mulch. I am sowing this weekend (a little late) all my fall cold hardy Italian varieties of lettuce. Any heading lettuce such as cos or butterhead will produce greens between now and the end of the year. Make sure you thin them as they grow. I like Winter Density, a great one for the fall.

When's the best time to plant tulip/daffodil bulbs for spring? I live in a condo so I"ll be using a large container. Is there anything I can plant on top of them for the fall/winter so I don't just have a bare container until Spring?

Daffodils can be planted now (or through the fall if they are stored well), tulips need colder soil, and I wouldn't plant those until October. If you get them early, put them in the fridge (not the freezer). You could plant pansies on top, for a show until December and to discourage the squirrels from digging up the bulbs. Make sure the container drains well and is freeze proof. 

I'm finally moving this weekend to an apartment with a small roof deck! I would love to eventually have some herbs and other edible plants up there. Is there anything I can get started this fall, or will I have missed the season? I'm a total novice and have never lived in a place with outdoor space!

Generally, the larger the pot, the better for everyone involved, though the initial planting may be more of an effort and expense. Use a potting mix, not topsoil or compost, and sprinkle some mesclun, lettuce or arugula seed on top, keep it moist, and you will have some ready greens in a month. 

I have a raised bed garden. I started with cheap pine boards, then went to oak--but even those lasted only a few years before rotting. Now I am using treated lumber that is supposed to last 20 years in the ground. Will the chemicals used to preserve the lumber affect the vegetables grown in these beds, and if so, are there health issues?

The industry switched from nasty chromium arsenate preservative a few years ago, but even the newer stuff is not great in the vicinity of edible plants. Put it this way: I don't use the treated lumber for my raised beds. I have used cedar planks from salvage yards, though the savings aren't  that great. I also use untreated pine and accept that I will only get two to five years out of  it. 

Not a question, just wanted to thank you for yet another gardening tip I got from you. After your repeated endorsements I bought a garden fork to use instead of my trusty spade to use for my fall planting. What a difference!--especially helpful in mixing in compost and breaking up Montgomery County's clay soil.

Fantastic, thank you. Sad to see people labor away with shovels.  

Can you take a question that's not specifically about fall gardening? I grow annuals, mostly marigolds, in boxes on my balcony, and have done so for almost 10 years. This year, for the first time, spider mites have been decimating my flowers. I tried using a commercial spray labeled for use with red spider mites, but nothing seems to kill the horrible beasts. My marigolds usually live until the first frost, but I have had to remove close to 75% of the plants because they were infested. Do you have any suggestions for the rest of the year and next year? Thank you.

First of all, don't use insecticides, which don't kill the mites but do kill their predators. Second, accept that mites are mostly a problem in hot dry seasons, the way this one has developed to be. Once it turns dry, you can hose off the mites before they build into large populations. Next year might be better. Perhaps you should try another annual, perhaps mounding zinnias or tithonias. Suggestions welcome.

Hello, I have a mature mophead hydrangea variety. I watered it some over the summer (read: not often enough). The flowers are all totally dried up. Is there anything that I need to do now to ensure that it is healthy for next year? Thank you.

The flowers are meant to dry on the plant, some have a beautiful sequence of coloration (Preziosa is one of my faves). The problem this year is leaf wilting from our excessive heat and lack of rain. Do keep them watered. Also, don't chop them to the ground in the fall/spring clean up: They need some of last year's canes to bloom next June. 

In Anacostia I have access to unlimited amounts of shredded tree stumps and limbs generated when city crews take aging trees down. I assume it makes an excellent mulch for top covering perennials over winter, My question is what ratio of this material should (or can) be mixed with soil to make a good top soil for actually growing plants in using containers next season?

Wood chips make a good if temporary path layer, and although they do take nitrogen as they break down, there's no reason not to use them in a compost pile if you can mix large amounts of green material with them: grass clippings, kitchen scraps, the vegetation from the garden. You could start a compost pile now and by next spring, it should be broken down enough to use in containers, but you would want to screen it first to get out most of the lingering woody bits. A pile breaks down more quickly if it at least a cubic yard in dimension, gets some moisture (but not sodden) and is turned monthly. 

I had a container full of blossoming geraniums and petunias. I awoke one morning to find all the blossoms gone! Will I get buds again? There is nothing left but stems.

Sounds like deer. They have found a new drive-in and are waiting for dessert. They might rebloom again this year if you can protect them, but it's getting late. 

My azaela bushes went into overdrive growth mid summer due to the rain. Is it too late to cut them back without impacting flowering in the spring?

I'd say yes, my earlier advice notwithstanding. See if you can remove entirely the lowest branches, which give it the most width. 

Several trees in our neighborhood, including my clump birch, have been invaded by something that appears to be a giant spider web. I know it isn't a spider, but what is it? More to the point, how can I get rid of it? Unfortunately, the thing attacks the trees at a height of 15-20 feet off the ground, which makes it difficult for me to get to.

It might be the fall webworm. Since it is late in the season, and the leaves have done their work for the year, it's not as serious as it looks. 

What's causing the webbing over branches of my trees? I'm told that tent caterpillars come out in May, but there seems to be an epidemic in the Howard County area of something similar.

And another question about the fall webworm. I don't think I would spray, particularly after reporting and writing this piece on our beleaguered pollinators. You could try and knock them back with a jet of water. Power washer, anyone?

Do you recommend "limbing up" tall trees (oaks, tulip trees) to get more light down to my lawn/garden?

Yes, if it is done sensitively and conservatively without upsetting the balance (physical and visual) of the tree. There is a knack to it, your first cut must be an undercut about a foot out from the trunk, a second cut outside the undercut, and then the third cut amounts to correctly removing the stub to leave the branch collar. Some of these boughs are big and dangerous, you may want to get a pro to do it. 

I thought mildew was a dampness problem, but my peonies and lilacs, as well as all our neighbors' peonies and lilacs, are covered with powdery mildew after a dry August. What do I do, if anything?

Powdery mildew is more of a problem in dry conditions. You can only treat it preventatively. I would cut back the peonies, their work is done. I'm not a huge fan of big hybrid lilacs in our climate for this reason. 

Are there any professional landscape/gardening specializing in Gardens for Butterflies/ I live in Reston Va. Thanks KG

I don't, but as I point out in today's story, just a few milkweed plants will sustain monarchs. I included a list of plants that draw butterflies, many of which you may already have. I would take a trip to the Smithsonsian's butterfly display garden, located at 10th st nw and constitution ave. Lots of good plants there, with labels. 

When I bought my three little pots of germander, they were standing up stiffly and I thought they'd make a nice border for one side of my herb garden. (I admit I had the crazy idea of a braided Tudor-style border with rosemary but I came to my senses.) They are twice as tall now, maybe nine inches high, and flopping over to the side completely. Do they always do this, and what should I do to make them stand up?

Germander responds well to trimming, but it's a bit late now. I would cut them back to about six inches next spring and then keep them trimmed as they grow.  

I've heard that fall is the time to repair or renew the lawn. When should I rake compost into my lawn, and how much should I use?

This is the month to repair, renovate or replace a weedy lawn, assuming turf type tall fescue. The key to success is to make sure the seeds have good soil contact and even moisture. Be patient, it takes up to three weeks for gemination. It has been so dry that I would soak the ground a few days before starting work. We're out of time. See you here next month. 

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Adrian Higgins
Adrian Higgins is The Washington Post's gardening columnist. Read his recent story on a late-season growth spurt in the garden and follow him on Twitter.
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