Saturday, May 24, 2008
Invasive plants go from hindrance to help
Libba Wolfe
Libba Wolfe's column appears twice monthly in Extra.
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One of the first things I noticed when I moved here from the flatlands of eastern North Carolina was the steep driveways. It seemed as if every house had a bank. The back yard went straight up or the front dropped straight down. Sometimes that was reversed. I'd never seen folks wear cleats to mow on a slant.
I've been thinking about invasive plants this spring. "Invasive" has an ugly ring to it but planted in the right place it is the perfect choice. A steep bank may be the ideal spot for a spreader that might be too aggressive for the rest of the yard.
My first project (and it's an ongoing struggle) in our yard was the short, extremely steep bank beside the driveway. I knew I had to get it planted right away because every hard rain produced a flow of red mud. The soil is almost impenetrable rocky clay but topsoil and mulch slid right to the bottom. Add to this list of delights its location in full sun, especially the baking summer afternoon blaze.
The obvious choice would have been ivy but I wanted a more varied and colorful view from the kitchen window. I got out the pick axe and got to work.
My experiments
First I hacked holes for two evergreen hollies and they're doing well. I ignored the recommendation to dig holes "twice as big as the root ball." Ha!
I wedged in some small caryopteris. I love its graceful silvery foliage and blue fall blooms. They have reseeded, and I encourage every seedling to take up space.
I ordered inexpensive bags of naturalizing daffodil bulbs that quickly spread by producing more bulbs. They certainly were not planted in the proper 8-inch deep holes but they've done well and even started to spread.
The daylilies have also spread. The special, refined varieties went in the good soil at the bottom of the incline. I've seen ditch-bank daylilies coming up through asphalt so I put them in spots where I could barely dig. They love it, and I'll probably have to divide them next year.
One of my favorite spreaders is perennial dianthus, "Bath's Pink." A 3-inch pot I put in three years ago is now a 5-foot-square, thick mat of, well, not evergreen but ever-silver, ground cover. Last month it was a mass of pink blooms with a strong spicy fragrance.
I thought it might work on the bank. Because digging is so difficult, I bought pre-retail plugs from a local nursery. The tiny slips have taken off. I have great hopes.
Anytime I see a plant label that says "ground cover" and "tolerates poor soil," it becomes part of the experiment. I've had many fatalities. This year I'm trying different spreading succulents. We'll see.
Be prepared for hardiness
If you're dealing with a bigger bank and better soil, there are more options. If you're envisioning evergreen shrubs, experts at local nurseries can help you select the right ones for your site. There are more shrubs for banks than junipers.
If you want a low ground cover and maybe some bloom color or variegated foliage, you have interesting options. There are many varieties of ajuga. Its early spring blue spires rise over foliage that ranges from green to deep burgundy. There's even a pale variegated ajuga. Although it hasn't taken off on my bank, it's usually a fast spreader in difficult sites.
Hypericum calycinum, commonly called St. John's wort, grows in full sun or full shade. I love its yellow blooms. Sweet woodruff is a great spreader on shady banks. Lamium maculatum also thrives in partial to full shade. Even the lamium galeobdolon "Yellow archangel" I warned you about last month might be perfect on a shady bank if you understand that nothing, but nothing, will stand in the way of its aggressive spread.
Ivy and perennial vinca are two popular covers for banks. Both are lovely but they are labeled tenacious and vigorous for good reason. They won't stop when they reach the stopping point you had in mind. You'll be clipping and pulling out. You may change your mind, but they won't change theirs.
Even after several applications of special, super-strength ivy killer, you'll find sprouts. The vinca will leap and grow at a rate that rivals kudzu's. I'm not saying "don't plant them." I'm just asking you to consider a plant's natural growth habits before you start digging.
Other thoughts
Another pre-digging must is weed elimination on your bank. Even though you are planting a cover to retard weed growth, it will take a few years before your ground cover is thick enough to do a good job. Any weeds you leave will take full advantage of the water and fertilizer you apply to get your new ground cover established.
Fall leaf cleanup is something else to think about. Balancing on a steep bank with a rake tangled in vines is no fun. A leaf blower seems to be the best solution.
Take a walk around your neighborhood. Drive around a new one. Make note of creative ways to handle steep banks. If anyone's working in the yard, stop for some information and maybe some cuttings. Browse the nurseries and read the plant tags.
Picking the right ground cover can make your yard more attractive and your life much easier. But pick the right one. They don't call 'em ground covers for nothing.
TO DO
It's time to get tickets for the fourth annual Hahn Horticulture Garden Gala. The theme is "Blue Ridge Blooms" and will feature music by the Celtibillies, who were recently chosen to represent the best music of Appalachia at the Smithsonian Folklife Festival. A new section, the Hahn Meadow Garden, will be dedicated.
I can tell you the food is delicious, the garden is lush, the company is fun and the auction is full of unusual plants and garden items.
When: 5:30 to 9 p.m. June 14
Where: Virginia Tech
Info: Visit www.hort.vt.edu/hhg/ or call 231-5970
