Adrian Higgins gave advice on tending your garden in the fall

Oct 31, 2013

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

I've heard that some gardeners think it's best to leave perennials alone in the fall while others believe in cutting back. What is your take? Are there some perennials that absolutely should be trimmed (either slightly or to the ground)?

Hello everyone and thanks for joining us on Halloween. There are certain perennials that I would not cut back but only to give them an extra measure of hardiness, these are marginal plants here such as agastache, gaura and salvias. I like to keep the old top growth of things for a few weeks because they have a way of capturing the frost in November in a handsome way. Other than that, it's fine now to cut things back, knowing that the new growth will erupt from buds that have already formed in the crown of the plant. Peonies have been looking ratty for a long time.

Here is a link to today's Local Living cover story on the age of giant pumpkins.

Hi Adrian, Can you offer advice on what is the best time to transplant an Azalea bush that is growing too close to the house?

Early to mid fall is a great time to move an azalea. Don't replant it too deeply, give it a light mulch and make sure that it is well watered. Azaleas do well in partial shade and not so well in full sun, where the lacebugs and mites do a number on them.   

I live in Portugal, and our weather patterns are similar to California. We made a large investment in several dozen pots of "Ville de Paris" geraniums in early summer, and they made a spectacular display. What do I do now to insure optimal display again next summer? Cutting them back? Fertilize? Cover them in plastic?

If you are frost free, you may not have to do anything. One option is to bring the geranium into a sun room and keep it going, another is to bring it indoors but stop watering and let it go dormant, repotting it in the early spring. Perhaps the best course would be to take cuttings now and root them over the winter. You will have vigorous fresh plants in the spring. 

Is it now too late in the fall to overseed a lawn in central MD? If so, when's usually the best time to in the spring to do it? Thanks!

The best time to sow cool season grass seed is Sept. 15 to Oct. 15. You could try this weekend and hope for a mild November. 

Or so I thought. It's baaaaaack! I can't fit a stump grinder through the gate, so I can only cut the stump. Any advice?

Mimosa is a soft wooded thing, the roots should come out pretty easily. I use a sharp axe and a mattock (along with sturdy boots and thick gloves). Attack a section at a time and don't think you have to do it all in one sitting.

What can I do now, at the end of the season, to help avoid scale infestation again next year? Jeff

We seem to be having some technical difficulties, let's hope they sort themselves out. In the depths of winter, I would use dormant oil to smother scale and eggs. Scale infestations are often the result of, not the cause of, a severely stressed plant. Ask yourself if your afflicted plant is in the right location and, say, getting enough water in periods of drought. 

I have some limelight hydrangeas. Is it time to prune or do I want until spring? How about the more old fashioned (not tardiva) hydrangeas?

Limelight is a variety of paniculata, so it can be pruned (a little) in late winter without affecting next year's flowering. However, your mophead or lacecap hydrangea should not be pruned hard or you will lose flowering next June. 

I'm thinking of planting an ivory Halo Dogwood in a very sunny western spot. Do you know if these plants are fairly hardy and deer resistant? Thanks!

This is a deciduous shrub grown for its winter ornament of red twigs. I don't think deer, thus, bother it much. The bigger difficulty is that it is rather hotter here than it would prefer. Keep it watered in dry spells and resolve to remove some of the oldest stems in March to promote new growth, which is more colorful the following winter. 

I'm a transplanted New Englander and boy do I miss those fragrant lilacs in the spring. I've got a sunny spot in my backyard - everyone tells me to plop a crape myrtle there but I'd love to go out on a limb (so to speak) and try the Betsy Ross lilac. I understand the National Arboretum developed it for warmer, more humid climates. Do you have any experience with this variety in this area?

Bred by pros at the National Arboretum. I haven't grown it but probably a good choice if you want a lilac. The only evident problem is that it is white flowering, not your classic blue purple. It's also quite big, meaning you have to give up a lot of precious garden real estate for a plant with a limited season of ornament. Smaller ones may work better, such as Palibin, or the Persian lilac. 

I want to plant some tulips in pots. Should I use potting soil (with fertilizer) or just regular top soil? Do they need to be placed in the sun over the winter? And should I place some kind of screen on the top to help keep deer/squirrels away?

They don't need sun until the foliage emerges. They will need drainage and I suppose you could use good garden soil but as a matter of course I prefer well amended mixes for pots. You will also have to cover them against squirrels, I use netting, but you could store them in an unheated shed for a few weeks. If you have deer, I would plant daffodils instead.

I have a 15' by 15' garden that has grown vegetables (with great victories and remarkable failures) for decades now, at least since 1985 when I moved in and planted my first row of seeds in the already-existing garden plot. I think both the plot and the gardener could use a break, and I am thinking of taking a year off to do some other things. What should I do now to prepare the ground to lie fallow through next summer that will minimize weeds and maximize soil happiness and health, so that when I come back to it the following year it (and I) will be ready and eager to grow.

I would simply chop up loads of leaves in November with your lawn mower and spread a very thick layer on this bed so (six inches?) so that no weeds show up. I would add some more next spring, and let the earthworms work on it for a few months. Anytime you see weeds, pull them and add more leaf mold. By the time you return to it in 2015, the soil should be superb and teeming with great microbes.

Adrian - I have a wooden deck about 10 feet off the ground and I planted a wisteria vine below it. My plan was to have it grow up the bottom of the deck (or maybe to the railing) and then have it spread out along the deck. Is this a good idea or will this thing take over everything and soon turn into an unmanagable mess? Will yearly pruning be required? Thanks!

It will take over and become a mess. Asian wisterias need to be winter pruned (skillfully, without removing the flowering buds) and, moreover, trimmed back regularly during the growing season to keep it in check and encourage flower bud formation. This is probably the wrong vine for your deck. I would consider a spring flowering Clematis montana or a cultivar of American wisteria called Nivea. 

We're planting some linden trees in our inner city neighborhood. What do you advise for amending really poor soil so trees will thrive. We plan to plant tulips and other bulbs around the trees as well.

Newly planted trees don't need or want heavily amended soil. This promotes unhealthy root formation, ironically. I know some landscapers who simply mix the excavated native top soil with mulch to lighten it a little. The bulbs can be planted in the vicinity of the tree, but outside its rootball. Make sure that any burlap and wire cages are peeled back from the trunk, after the tree has been planted. 

When can I transplant some Rose of Sharon bushes - now? Or should I wait until all the leaves have dropped?

You could do it now, it's going into dormancy.

I have some huge hybrid lilies that have outgrown their current location. Can I move them now or should I wait until Spring? Is there any special soil amendment I need to make? Thanks.

You may be talking of true lilies. A lot of people call daylilies lilies, which they are not, they are completely different creatures. However, both lilies and daylilies can be lifted (carefully) and replanted now. Especially with lilies, it's important to dig the bulb with as little trauma as possible, and they should be replanted quickly because they are not truly dormant like, say, a daffodil bulb. Lilies like to be planted deeply in good, rich soil, preferably with the roots in the shade and the flowers in sun. 

What would you say is the one best thing someone can do for their lawn, right now? (central PA here, if that matters). Thanks, so glad you are chatting!

Perhaps core aeration and topdressing with compost. Now is also a good time to fertilize the lawn. 

Is now a good time to put in a climbing rose?

If you could find one now, yes. Bare root and container roses tend to be sold in early spring. Choose your site carefully.

I bought beautiful mums from a large, box-store retailer about a month ago that were full of blooming flowers. Now all of the flowers have turned brown. The mums are in a mostly sunny area but my soil is mostly clay. We haven't had a frost yet so I'm perplexed as to what happened to them. Did I just buy from the wrong store or plant them too late? thanks

Brown as in faded, not brown as in dead plant, I assume. Retailers sell things when they are in bloom, knowing that that appeals to our impulses. Mums blooming in September have been forced into early bloom in a greenhouse. If you want to keep the plant, you can groom it by removing the faded flowers. It will bloom later next year in your garden. 

I have a similar area and planted a carolina jessamine (spelling?) - it's gorgeous and does very well in that spot. And it's easy to prune to keep it looking good.

That would be a wonderful addition to a deck railing.

Hi Adrian, this year I saw some weeds that the leaves looks like starwberry leaves in my lawn. What kind on weeds is that? How to get rid of them before the overtaking my lawn? Help please !

This is wild strawberry, which spreads like the cultivated kind: A rosette puts our radial runners, which then root and form new plants. If you don't get it now, it will take over, believe me. After a period of rain, when the soil is moist, you can artfully feel for the rosettes and pull them out.

My Christmas cactus started getting leggy, so I put it into a deeper pot and it went to town. This was no more than a year ago. It's getting leggy again. What do I to to keep it from becoming Audrey Two?

It's meant to get leggy, and hopefully, segmented enough that it becomes pendent. Put in on a stand so that it can form a pleasant mound. 

What should I use when planting my tulips? Bone meal?

It certainly won't harm it, but bulb feeds are more useful in the years after the first flowering. You could scratch in some bonemeal or other organic feed in March as the bulb begins to bud. I'm not a big fan of bulb feeding, preferring to plant the bulbs deeply in tilthy soil. 

I wrote in a couple weeks ago and you took my question about indoor basil with a grow lamp, but your answer looked like it belonged to a different question. The basil is still doing well. The leaves aren't getting quite as big, but it's still healthy. Considering what basil costs at my local market (only sold pre-packaged), the lamp has already more than paid for itself.

Ok. But think of the cost of heating and lighting the basil. 

YES to the leaves! You said this many years ago and I've been mulching with leaves ever since, every fall, then digging them in in the spring. My soil is gorgeous.

Thanks for the vote of confidence. The little creatures and microbes that break down leaves just go to town. If you shred them a little first, you've done weeks of work for these wee beasties.

What are your thoughts on a Chinese Abelia (versus one of the more popular hybrids)?

I think it has its place in poor soils and exposed beds. It's tough and handsome and long flowering, and lower growing than the regular Abelia grandiflora.   

How much should I water my plantings in the fall?

Last question I'm afraid. Evergreens needs a good drink going into the winter. The drought has broken, which is good, but i'd still water things like camellias, azaleas, hollies etc. Newly planted shrubs and trees should be watered thoroughly when planted, but not repeatedly, or they will die from root rot. Thanks for all your questions, sorry I couldn't get to all of them. See you here soon, I hope. 

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Adrian Higgins
Adrian Higgins is The Washington Post's gardening columnist. Read his recent story on how to move a prized tree and follow him on Twitter.
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