The Washington Post

Adrian Higgins on spring gardening

Courtesy Ball Horticultural Co.
Apr 14, 2016

Washington Post gardening columnist Adrian Higgins took questions on gardening.

Is there a reliable way to know if the rhubarb that's been long up and sporadically protected from the frosts we've had is ok? I gather the oxalic crystals go into the stalks from the leaves if frozen, rendering them inedible. Some of the leaves are obviously wilted with rubbery stems, while others seem normal. Thanks.

Greetings everyone. I hope you're all enjoying the spring, which so far has been both hot and cold -- seeing some frost damage on a few things, but not as bad as I had feared. Rhubarb is grown for the leaf stalks, tart and delicious, but the leaves contain a toxic glycoside. I haven't heard of this compound moving to the stalks in a freeze. I suppose it's possible, but when I think of all the rhubarb clumps in Northern Europe and the constant dance there with frost in spring, I would have thought this phenomenon would be well known. Anyone else heard of this?

Here is a link to Adrian's most recent story, on assembling and caring for a succulent garden.

I live in "The Valley", the Shenandoah one, and put Yukon Gold, Red Pontiac potatoes in around St. Patricks day as 'the signs' dictate. Usually this works out fine, but of course this year we've had endless flurries, overnight freezes, etc. Do you think the crop may be lost or can the cut pieces withstand the delay in sprouting?

If I were planting in cold soil with sliced seed potatoes that had not been sprouted or chitted first, I might worry a bit about them rotting. I try to get small seed potatoes and don't cut them so that I don't have to worry about rot so much. If I did cut them (to increase seed amount), I would certainly let them cure for a few days before planting and perhaps dust with a sulfur powder. I usually put mine in  in late March (there's still time), and I don't bother with sprouting them first, and they grow fine.    

I have heard that ducks will eat harmful insects in the veggie garden and I've had awful trouble with cabbage bugs. What kind of ducks should I get?

Hungry ones. I haven't kept ducks, I would worry about them scratching and generally uprooting transplants and seedlings. I know gardeners who like the walking ducks. Any you get would have to be protected from predators. Any duck minders out there?  

Adrian - My hydrangeas have really taken a hit over the past couple of weeks - all the tender green leaves have been damaged by our recent cold spell. Do you think there's any hope that they will flower at all - did the cold also damage the buds?

The frosts followed an early spring and did real damage to hydrangeas. Just leave the shrubs alone and see what grows back before doing any grooming, pruning. They may flower, if somewhat not as much. This is why reblooming hydrangeas have become all the rage.  

Is the bloom schedule early this year due to the warm winter? I live in NYC and I've seen lilacs already blooming, and they usually don't come out around here for another month. Also, my daffodils bloomed in February, then got killed by a cold spell. Do I need to replant them, or will they grow back next year like they usually do?

The Tidal Basin cherries bloomed early, in late March, but dodged the frost bullet, which came after flowering. Some blooms are three weeks ahead of schedule -- my single late tulips are now in flower and in prior years they would have bloomed in another two weeks. I think a lot of gardeners have given up viewing anything as normal and are resigned to enjoying flowers when they appear. It's unusual for daffodils to die from cold, they will flatten if it gets down to a deep freeze, and the flowers will get damaged when it's really cold. Jonquil daffodils like hotter conditions and may be damaged by late freezes, but they wouldn't have been in bloom in  February.You don't say if the daffodil foliage has been killed, but I would leave the clumps well alone and see what happens next year. Lifting them now won't be of any help.

How best to encourage zoysia grass to completely take over a lawn? Right now it is only in patches, so in the cool months it looks like a patchwork of brown and green.

I would take a long handled bulb planter and extract plugs to replant in the areas where you want them to spread. You may have to cut your cool season grass shorter or more often to prevent it from smothering the zoysia as it spreads. 

Hi again Mr. Higgins - I have one fairly sunny spot in my garden and last fall I moved some boring bushes and planted a couple hundred tulip bulbs -- and they are making a glorious display at the moment, so I figure I'll do it again this fall. Any ideas for what to plant there over the summer so that I can add bulbs in the fall? Annuals I assume? Afternoon sun, and would love not to have to water every day. Thanks!

I have a little border where I grow dahlias and tulips. I lift the dahlia tubers in November for overwintering, and then stick in the tulip bulbs. I pull those in early May after flowering when the dahlia tubers are ready to start growing. This system is based on the idea of discarding the tulips, the best approach for most hybrid varieties. 

When is a good time to divide irises?

Bearded irises are usually divided in mid to late summer. Here is a link to the American Iris Society website

Have you planted your beans yet? My experience is if in when the soil is still rather cool they tend to rot. Also folk should be reminded not to rush with the tomatoes until evening temps above 50.

Good advice. I know people who have sown beans already, but I think they will regret it. White beans tend to rot in cold wet soil more than other colors, but I wouldn't sow any green beans until early May, and I wouldn't sow lima beans until late May. My tomato plants are still safely indoors under lights. When they get leggy, I pot them up and bury the stems a bit. I won't plant my tomatoes until the first week in May at the earliest. 

My beautiful dwarf Japanese maple was leafing out before the last freeze and now most of the leaves are withered and brown. Will it leaf out at all this year?

What a shame. Mine (in Alexandria) seem to have been spared. I wouldn't do a thing, except wait to see if they resprout. You might want to give them a boost of balanced fertilizer to help them out. 

I have had a craving for a few years for a white, fragrant Lilac. Found one a couple of years ago but it died without advancing much. Do you have any suggestions for one that will do well in our area? Many thanks!

I'm about to write about lilacs so keep checking our website this week. I'm not a big fan of white lilacs, but if I were to grow one, I'd pick Betsy Ross, which is a National Arboretum introduction adapted to warmer climates. 

Mr. Higgins, I've gardened on a wooded lot in Reston for nearly 20 years. I don't have any grass, and have tried many times to transfer moss that's grown on my brick patio to bare-ground areas where I have no plantings, pachysandra or hardscape. No luck til this spring, when I suddenly have a beautiful explosion of moss on these areas. No idea why it came up this year, but it looks wonderful! Is there anything I could be doing to nurture and maintain it so it survives and summer and comes back next year? Thanks for sharing your knowledge!

If you were 50 miles west (at a higher elevation) your moss might be happier, but you can develop a moss garden with a bit of persistence. Moss likes shade and poor, compacted soil. It loves moisture but isn't a swamp plant. So find a patch of clay in the shade, plant and peg some moss sheets in the area, and give it  a spray of water regularly, especially if things turn dry. Keep it free of fertilizer and fallen leaves and other litter. This is one instance where a leaf blower, gently yielded, may be better than a rake. The moss may brown out in the summer, but will spring back when it gets cool and moist again. 

Hi Adrian, I am looking to start a container garden or window boxes on a garden and am at a loss as to where to start. Can you suggest any good resources on how to determine what size containers to get and what type of plants? We get a lot of afternoon sun, if that helps.

Check out my huge feature this week on succulents, which would be perfect for your situation. I would be inclined to use hypertufa containers on  a balcony, for weight reasons:

I'm looking to do some container gardening on my patio. I plan to buy small plants at the store rather than starting from seed, and I'm looking to grow herbs, tomatoes, and berries. When should I plant them for best results? (I'm in Northern VA.)

And if you don't want succulents, I would grow such things as sweet basil, parsley, thyme and oregano in containers, remembering that the pots must drain and that the larger they are, the less stress on the plant. I would plant determinate varieties of tomatoes in containers. As for berries, few would be happy in a container with the exception of strawberry plants kept well watered. 

Hi Adrian, you wrote an article several months ago expressing a lack of love for amaryllis bulbs. You were so right! I was given a gigantic bulb at Christmas. The sentiment was great - it's a flower, it's biodegradable, no waste for the landfill or recycling. I dutifully planted the bulb according to the directions, and waited... and waited... and waited... It sloooowly sent out a stalk. And because this was a giant amaryllis, the stalk kept getting taller and taller. It wound being a single 2 foot tall stem. It finally sent out a few flower trumpets at the top, which lasted 2 weeks. So that's roughly 10 weeks of waiting and giant stem, for maybe 2 weeks of flowering. It was pretty funny, honestly. Little return on the time invested.

Amaryllis are inscrutable. I planted 10, most of which shot into growth and bloom. One is still sitting in its pot, jsut showing a green tip. Maybe I should start talking to it, avoiding the word, Runt, at all costs. 

I've have been pleased that a clump of French tarragon wintered over nicely, but as I experienced last year, the new growth no longer has the wonderful licorice taste. Is this a spice that should be considered an annual?

It's conceivable that the desired flavor will express itself in the new growth, so wait a month. But I view many perennial herbs as annuals or biennials in our climate, and part of the fun of spring is planting afresh. 

They'd started to bloom before that last freeze and are now drooping and brown. I know they won't bloom again this spring but will they survive?

I would hope for another flush of growth, but coddle them this spring with some fish emulsion or the like. 

Our small backyard needs some screening from the yard of our next-door neighbor. A fence is one idea, but are there landscaping options you recommend? For what it's worth, I don't like arbor vitae.

My advice for years has been to give up trying to block out every unwanted structure, but to create a diversion for the eye. This can be achieved by installing an attractive fence -- it might be something as simple as a paddock or picket fence -- and then clustering a planting in front of it. I have become a big fan of Eastern redcedars as a medium sized evergreen screen. Brodie and Evergreen Sentinel are good cultivars for this.  

Should they be put away for the summer? Do the birds do anything helpful for the plants that would make you leave the bird feeders out year round?

Ironically, this is the time of year when birds need feeding the most, because all the winter berries and seeds are gone. Keep cats away from your feeders. 

Hi, what flowers are your favorites to brighten up balcony with lots of afternoon sun? They will be in (large) container pots, so something hardy and heat/drought resistant is a must!

I would pick some lantana cultivars and calibrachoa, both of which take hot, dry conditions. Zinnias are good too. Folks, we've run out of time. See you back here soon.

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Adrian Higgins
Adrian Higgins is The Washington Post's gardening columnist. Read his latest columns and stories here and follow him on Twitter.
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