To keep grape hyacinths from taking over your yard, plant them in a few inches of soil on top of concrete.
Grape hyacinths (Muscari species) are charming spring bulbs. The “grape” in the name presumably refers to their small balloon-like flowers that grow in clusters that resemble upside down bunches of grapes.
However, these little plants can be too much of a good thing. Below is a picture of them taking over somebody’s yard.
When I bought my house, there were numerous clumps of grape hyacinth spreading through the garden. When conditions are good, grape hyacinths can multiply rapidly. Below ground, new small bulbs bud off old ones. Above ground, they scatter seeds. Where they become abundant, the soil can be a nearly solid mass of bulbs!
Be careful digging them out. Any scattered dirt can spread them around. I managed to beat them back to manageable numbers by lifting out chunks of soil and literally cooking it in a glass bowl in an old microwave oven.
Now, I enjoy grape hyacinths in moderation. Prevention is better than cure. That means making sure their growing conditions are, well, not so good. It’s helpful to understand the ecology of bulbs.
Our familiar spring garden bulbs evolved to survive through an inhospitable part of the year, usually a dry summer. Also, lack of sunlight for photosynthesis, such as under trees that leaf out and cast a dense shade. During this off season, the entire life of the plant is in the bulb. There are no stems, flowers, leaves or even roots. In this state, bulbs are remarkably resistant to drying out, and to freezing.
In the brief time of year when conditions are good, bulbs leap into action. They “spend out their bank account”, rapidly pushing up leaves and flowers. While the good times last, they capture solar energy to create next year’s bulb. As soon as conditions worsen, the plants shut down operations, and retreat back into bulbs. If the overall balance sheet for the year is positive, the plant shows a profit: A bigger bulb than it started with, a few new side bulbs, or some seeds.
This is why you are advised not to trim off the ratty foliage of, say, your tulips and daffodils, after they have bloomed. The plants need those leaves for photosynthesis, to restock their bulbs.
If you have ever “forced” bulbs, such as paperwhite narcissus, or hyacinths, you can see why they are typically treated as a one-time thing. The bulb has enough “bank account” to flower, and make some leaves. But after that, it’s pretty much broke. The conditions to restock are not there. You had the bulb in water, with none of nutrients it would normally get from soil. It’s in your dimly lighted house, where it can’t photosynthesize. If you do stick it out in the ground, the indoor-adapted leaves sunburn and the water-adapted roots struggle to adjust. If the plant does survive, it retreats to a bulb much smaller than the one it started as.
The Pacific Northwest is heaven for bulbs. In our mild winters, they get started early. After they bloom, they have a long, moist springtime to rake in the photosynthetic profit. Many of them open branch offices. A few tulips or daffodils soon become dozens.
It’s not like that everywhere. I lived for ten years in Colorado, where summer slams down hard. Tulips would bloom, then shrivel in the baking heat. Whether they pulled ahead or fell behind would be a matter of microsite. For example, on the north side of a fence, the soil was shaded and stayed a little more moist. In spring, tulips would stay alive long enough to replenish their bulb, plus store up a bit extra. Each year, there would be more blossoms. But on the south side of that same fence, tulips would slowly fail. They dried down early. In a year or two, they stopped blooming, only put up leaves. The leaves got smaller every year. Unless rescued, they would finally die.
Incidentally, here’s a trick to rescue bulbs, or just move them when they are in the best stage to move, namely completely dormant. Maybe you think you’ll remember where they are. But lo! Those lush blooms and foliage disappear without a trace. It’s midsummer, and the ground is hard and dry. Maybe you poke around with a trowel, and occasionally stab one of the bulbs, and cut it in two. How can they hide so well? Next spring, there they are back again, blooming. But at that stage, it is very stressful on them to be moved.
Here’s the trick. When the bulbs are blooming, slip a bamboo skewer down beside each stem. A package of 100 costs only a few dollars. If you accidentally poke into a bulb, it does little harm. Then, just wait for summer. The skewers look significantly different from anything else likely to be in your garden that time of year. The ground is dry. Just tunnel down by each skewer, and there is your bulb. If you want to sort out different kinds of bulbs, make up a barcode, and mark each skewer with a grease pencil (all other kinds of ink fade away). Say, one band means yellow, two means purple, and so on.
Different kinds of bulbs are more and less aggressive, and grape hyacinths are the toughest ones I know. Take note: Grape hyacinths start pushing up new leaves after the first rains of late summer. So, they are in business months before anybody else! No wonder they multiply like mad.
So here’s the method to control them. Put a few inches of soil on top of bare concrete. Use the worst soil you have. Plant grape hyacinth bulbs in that.
In the winter rains, the bulbs will grow. In spring they will bloom.
But as soon as the rains slack off, the season’s over. The minimal soil dries out, and the plants go dormant. They do not get to spend the long luxurious spring months drawing moisture from the subsoil, to increase themselves, and bud off side buds and make seeds.
They just about break even. They will sleep all summer, and be back next spring.
Here’s an actual planting done this way. The concrete steps run right over to the adjacent concrete foundation. There is no other soil. (This photo is from late March.)
The large straplike leaves mixed in are tulips. The tulips produce leaves every year, but have not been able to make enough headway to bloom.
In May, as things dry out, the grape hyacinth plants are packing away everything they have into their bulbs. They do not have the resources to even try making many seeds. In the photo below, notice how few pods there are. Some of these are not even filled. If the stalks do manage to ripen a few seeds, they are stranded out on the concrete, not likely to fall any place they can grow.
A similar method, using the same principle, is to confine grape hyacinths to pots. These look pretty good when in full bloom. They fill out, and don’t even look like potted plants.
Put they are entirely in pots.
I have a line of these pots set, again, on top of concrete, up under an overhanging eve. They get only the rain that drifts in on them during the winter. They provide some welcome spring color, then die back and disappear for the rest of the year.
They start growing as early as September. These started after an anomalous August rain.
There are some other flowers I treat in a similar way. I grow them where they can barely survive.
This is Kenilworth ivy (Cymbalaria muralis).
Here, I have it on a mossy concrete block in the midst of, you guessed it, an expanse of concrete. It gets a little drip irrigation overspray during the summer, but not much. This plant is so invasive, I don’t let it get anywhere near topsoil! Even this little patch of it, I come along periodically and rip half of it out.
This is the annual forget-me-not (Myosotis sylvatica).
Yes, they have pretty blue flowers in the spring, but each plant can make thousands of seeds. Here, I’m letting it root where it can, in chinks at the base of a concrete block wall. These blocks are not on the soil, but on top of (somewhat dirty) outdoor carpet. The plants manage to snake their roots down enough to grow and bloom. But they die when the weather turns dry. Even so, they still make more than I want, and I weed out the extras,