Adrian Higgins gave advice on how to nurture your garden in the fall

Oct 18, 2012

Get tips on digging, weeding and seeding your garden

Hi there, Hello! I just lost a couple of green giant arborvitaes, and I suspect they were sitting in too much water. I'm thinking about replacing them with a bald cypress or sweetbay magnolia. Prefer something that doesn't get too wide and evergreen, if possible. Also, indigenous would be nice! Your thoughts?

Hello, and thanks for joining me today. My story today is about tulips, and I have just ordered about 500 now sitting in my refrigerator. (Occupational hazard). A narrow tree for a moist spot: There is a variety of Magnolia grandiflora called D.D. Blanchard that stays pretty narrow. Another good choice would be the bald cypress or the yaupon holly, both native. 

What are the best cover crops for this area to fix nitrogen levels? When do these cover crops need to be planted? I obtained a community garden plot this year and though overall I had a very good first season, I did experience problems caused by low nitrogen levels in the soil. Organic fertilizers helped, but I'd like to improve the soil over the winter if I can.

I would sow red clover or hairy vetch. It's getting a bit late, but not too late. Both are legumes that will put nitrogen into the soil. Cut them in March and dig them in for additional nitrogen. 

Here is a link to Adrian's story about tulips in today's issue of Local Living.

Do you consider Mexican petunias to be invasive in our area (DC)? Thanks.

I have not grown them (Ruellia britonniana) but it is a tender shrub, much like lantana, and the frost will kill it here, so invasiveness shouldn't be a problem. Apparently it's a problem in Florida.

I have a border of yarrow planted along a gravel path that has really faltered in the last two years. It's scraggly, and barely blooms. I'd like to dig it up and replace it with something of similar height to form a border along the path. That section transitions to some rose bushes, lilies and lambs ear on one side of the path, and daisies on the other. Any suggestions of a good plant that will thrive in clay soil, spread easily, and fit in well with more of a "cottage garden" kind of design? Thank you for your help.

If it has plenty of sun, I'd consider good old black eyed susans. If not, I would plant a hardy geranium as a ground cover.

Adrian - Nice to see you and I wish we had you weekly! I have a house in the Blue Ridge with a very big yard that has (mostly) Tulip Poplars spread out about 75 feet apart in all directions. All are mature and some are dying. What would be some good replacement trees for the long haul? We have a bunch of Dogwoods interpersed, but I'd like replace these big guys with similar sized beasts. Any suggestions for some things that will fit in well in this area, ie natives? Thanks!

Thank you for your kind welcome. I miss the weekly chats. If you are at some elevation, you can plant trees that don't fare as well in DC. I love the Eastern white pine, even though it is not well used in the city. It's a conifer for an upland property where it can have the space to spread. One major problem is disfigurement during ice storms. (You don't get those in the Blue Ridge, do you?) (Joke).  I would also consider the white oak, the red maple or the sugar maple, the last stressed by the heat of the city. 

Whats the best way to enrich your garden soil over the winter?

You can grow a green manure such as vetch, clover or rye. Or you can lay a two inch layer of leafmold or rotted compost. Incorporate it into the soil in February or March. If you do this every year, your soil will turn from heavy clay to beautiful loam in about three to five years. 

Greetings. Thanks in advance for your help. My entire back yard (which is pretty small) is a perennial garden. One of my ongoing challenges is to find plants to extend the season. I'd welcome some suggestions on early blooming plants that can start the season earlier than late May/early June, and late blooming plants that would extend our enjoyment past the peak in early August. I also have a mostly clay environment and try to stick with plants who will thrive (or at least be relatively content) in the environment I have to offer. I am particularly partial to native plants, and already have things such as joe pye weed, hydrangeas, daisies, black eyed susans, etc. I have a range of full sun to part sun. Any suggestions for me?

For early perennials, I would consider hellebores (not native but fabulous), a spurge named Mrs. Robb's Bonnet and Geranium macorrhizum. For something late, I would try some persicaria 'Firetail'>

Adrian - Is it too late to plant hyacinth bulbs for the spring?

No. Generally, the earlier the bloom in the spring, the earlier the planting in the fall, thus crocus and snowdrops especially would like to be in the ground by now. So would daffodils, but late planting is fine (It may delay the first bloom season). Others can be planted as long as the ground isn't frozen. Tulips don't start growing until the soil is below 60 degrees. 

Last winter I planted tulip bulbs in clay soil, watered once a month, covered with newspaper and placed on a shelf in the garage. The foliage was wonderful, but there were no flowers! What did I do wrong?

I think your garage was too warm. Tulips need eleven weeks of temperatures below 45 degrees for the flower to develop.

Can we have you chat with us more often than once a season? :-) When is the latest that we can sow grass seeds in our area? Also when is the latest to use broadleaf herbicide effectively here?

Talk to my bosses at the Post. :) I'd say this is the last weekend (or maybe the following) to sow cool season grass seed. Broadleaf weeds need to be in active growth for the herbicide to work. It's getting late for that, I would think, and though broadleaf herbicides are designed to work against dicots, I'm not sure I would apply it if I were seeding grasses (monocots). 

Hi Adrian, A friend pointed out that I have seeds on my mature Japanese Maple. What is the best way to grow this plant from seed? Many thanks!

Wait for the seed capsule (samara) to dry on the tree, or pick up windblown ones, and sow them in four inch pots filled with a potting mix. Keep the pot a little moist and outside in a protected area over the winter. The seedlings will be variable, and not a clone of the mother tree. 

I just wanted to say how happy I am to see you live-chatting! I am very much an amateur when it comes to gardening, and I am grateful for everything I learn here.

Thank you so much.

Hello Adrian, I had some impromptu landscaping done last week. I live in Maryland and we planted yuccas, nandinas, asters and abelias. However, I am concerned about their survival after this winter. Is there a good chance they will make it? Is there anything that I can do now to help them endure the upcoming weather? Thanks in advance.

Now is the best time to plant shrubs and perennials. The soil warmth will encourage root growth and the transplant shock is minimized by the cooling temperatures. Just make sure they are well watered (but not flooded) and mulch them after the ground freezes. This will minimize the risk of freeze-thaw exposing the roots. 

My one-year old Zepherine Drouhin climbing roses are about nine feet tall -- do I prune them back now before winter? Tie them securely to the trellis and just prune anything that could be tossed by the winter wind? FYI, they blossomed in May, but haven't since their aggressive growth spurt this summer. I don't think they'll hip out before the first hard freeze.

This is an antique climber that is supposed to repeat, but the repeat blooming is  but a faint echo of the first show in May. In February, you should cut back this year's growth to stubs bearing about four buds each, they will erupt as flowering branches in March and April. The more you can train the keeper canes horizontally, the better the flower display. 

I have been reading a lot lately about leaving rather than raking leaves from garden areas as a way to enrich the soil and not use so much mulch. Do you think this works equally well in shade and sun, and is it necessary to shred the leaves? Some say yes, some say no. I don't have a shredder so I would rather not. The leaves are a mixture of oak, maple, and sweet gum mostly.

I like to shred them, they break down much quicker and don't mat. I use a lawn mower set at its highest setting. This sometimes means raking the leaves onto the lawn, shredding them, and raking (or blowing) them back. It's a chore, but worth it. Bagging leaves is such a waste of a valuable resource. 

We have a small garden, maybe 6 x 10. There's a strawberry patch and a grape vine. We generally plant tomatoes, peppers, and squash. We seem to have problems with our tomatoes not growing as well as we'd like and the grape vine only produced a couple of bunches this year. What should we do this fall to better prep and restore the soil so that our plants will produce as much as they can? Thank you!

I had poor luck with tomatoes this year (but great luck with peppers). I think it was too hot. I tend not to grow strawberries because, as perennials, they take up a lot of precious real estate that could be productive all season with something else. The key to good fruiting in a grape vine is winter pruining. You want to train it to have two or four laterals, and prune them back in winter to seven buds or so. 

I read your article on tulips today with great interest. Although I love tulips, I am too lazy to treat them as annuals. In the past I had good luck with the Darwin hybrid Pink Impression, which reliably returned for at least 5 years (then we moved so I don't know). Have you found this to be the case or was I just lucky?

There are some hybrids that come back, especially those of the Grieggi. Fosteriana and Kauffmania species. I just find that most hybrids return so weakly, and that life is too short for wan tulips. That's my philosophy.  Pink Impression may be a great perennial, good to hear.

Just wanted to say thank you for acknowledging that tulips can be grown in containers. We're moving into the city and will have no flower beds at all. I was very sad to be leaving my tulips and daffodils behind; knowing I can grow them in containers perked me up! Thank you for the tip! (And I'll gladly take any more container ideas you'd like to share!) :-)

Thanks. I really like Angela Jupe's idea of taking a dark container and stuffing it with Exotic Emperor.

Dear Mr. Higgins, my dear husband gifted me one of those tent-like greenhouses for our first anniversary. I would like to do some gardening in there this winter. But how do I even begin? What plants should I start with? Herbs? Dwarf citrus trees? Salad greens? Tropical plants? A link to a resource would be helpful, too. Thanks, as always.

I would start simply with salad greens and things like lettuce, spinach, chard and kale. I assume you're not heating the greenhouse, and all these hardy greens will love the extra protection of a cool house. You must make sure it ventilates on mild, sunny days, or the temperatures can reach 80 degrees or more, seriously stressing you plants. You could also grow hardy herbs such as parsley, thyme, oregano and rosemary. 

Last winter I had to move my peonies when we relocated from Loudoun to Fairfax. I put them in as sunny a spot as I could find, trying to get as close to where they did well at our previous home. This house has far more mature trees than our old house, so the options were somewhat limited. They didn't flower at all this spring, did not grow nearly as tall, and some of the leaves were a bit browned, even in the height of summer. Is there anything I can do this fall or winter to coax them back into blooming for the spring? When do I contemplate whether they need to move to a different location? I'd really like to save these peonies, as they belonged to my grandmother's aunt, and have moved several times with me. Up until now it has always been with great success.

The crown buds should be buried between one and two inches to promote flowering. Peonies don't like being moved, and they are probably just sulking. Give them a year or two.

Hi -- We have 16 40-year-old avocado trees of various flavors (basically, everything except Haas). Each year about half of them bear fruit and half don't. Any suggestions on evening that out, or is that just the natural cycle? Thanks.

You're taunting us up here in the frigid north. I don't know, I've never grown avocados into trees, but they do benefit from cross pollination for a good fruit set.  In a wet year, the pollinators tend to stay home.

Adrian, my back yard is quite the perfect shade garden or would be if I could figure it all out. The biggest problem is an elm tree that grows in one large bed area and hogs all the water and has many large roots passing below where I cannot dig a hole to plant. So the bed has barren gaps featuring mostly shredded mulch and some creeping jenny. Prostrate yews grow well to one side on a small rise away from the roots. But heuchera, toad lily, astilbes have all failed. Trying some ferns this year. Any thoughts for 2013? Thank you.

I think I would try some hellebores, which can take dry conditions once established. 

Hi - I'm the one asking about the tree for for moist soil. Are there any vendors you can recommend? Do I just go into a nursery and ask them to order and plant it? Thanks.

I don't recommend vendors (a slippery slope), but go by species and variety and remember that a smallish tree establishes much better than a larger one and soon catches up in size. The nursery is the place to examine an individual specimen to make sure that it has the central leader that you would want and doesn't have nasty trunk injuries, etc.  I remember mail ordering buckeyes once and they arrived with significant rodent damage on the bark and the nursery gave me a hard time when I insisted they replace them. If you can see the plants before you buy, so much the better. 

When should glads be pulled out of the ground? We've not had a freeze yet. Once they are lifted, how should they be stored? Thanks!

Traditionally, you dig them in leaf in the next few weeks and then set out the bulbs to cure in the sun for a couple of days. Cut off the leaves and store the corms in ventilated bags in a cool area that doesn't freeze. (A cool cellar, perhaps).   Plant them in the spring.

The last two summers have been so miserably hot that I haven't been able to stay ahead of the brambles that are taking over the azaleas that form our foundation planting on one side of the house. Is the only solution to dig up the whole hedge, pull out the brambles, and try to stay ahead of them next summer? They're so thorny that it's a major job to crawl under the azaleas to try to cut them down.

Brambles root where they touch the ground, so you can't ignore them unless you want a bramble hedge. (Great cover for cat stalked birds). If you wear thick pants and a long sleeved shirt and heavy work gloves, there is no reason not to tackle them. Use a garden fork to uproot them. Alternatively, azaleas are easily dug, and can be moved now.

I planted one of these a few summers ago since you said they were supposed to be hardy in this zone (I'm in Ellicott City) but I wasn't too surprised when it died over the winter. I put in another one this past spring and it has gone hog-wild, spreading beautifully. Is there a chance it will live since it's gotten so big, or do I just plan to buy another next spring?

They're supposed to be perennial here. That's the adventure of gardening, you don't know what type of winter lies ahead. I have a friend who is convinced we are going to have an awful winter this year because last winter was so mild. But who knows? Certainly not the almanacs. 

I bought (I think on your advice) a sharp, thin hoe for weeding (mine is a collinear hoe from Lee Valley). I was out using it last weekend, getting after all the cool weather weeds that seem to spread a foot a day this time of year. Anyway, after slicing under the weeds, I'm left to wonder whether I need to gather up all the bits and pieces. Or is simply cutting them off at the roots good enough?

This has to be the last question, sorry. So glad you are using a hoe and not chemicals. Thank you. Keep a file handy to keep it sharp. If the weeds are not flowering and seeding, you can let them lie on the ground, they will enrich the soil as they decay. Loads of weeds are now germinating for the winter. Don't wait until April to attack them. Thank you for all your questions: Keep reading gardening advice and fun stories in Local Living and other parts of the Post. 

I just want to say that we miss you terribly! Welcome back and hope to hear from you soon. - Richmond, Va

In This Chat
Adrian Higgins
Adrian Higgins is The Washington Post's gardening columnist. Read his recent story on the National Arboretum's koi sale and follow him on Twitter.
Recent Chats
  • Next: