As a garden designer, I’m always recommending plants to plant. A good, fragrant shrub for below a window. A plant with blooms in late winter. A disease-resistant perennial for shade. It’s one of the funnest parts of my job. But sometimes it’s even more important to know what plants to stay away from. They are invasive perennials. Not just because they replicate quickly but because you will most likely never be able to rid them from your yard. Take Bluebells (Hyacinthoides non-scripta) or English Laurel (Prunus laurocerasus) as examples. People plant them because they’re pretty or useful, then realize after several years they have a problem on their hands. Here are the top three invasive perennials (or grasses) I see in clients’ yards. They bully out other plants and drastically take over the garden bed. They may or may not be on the noxious weed list, but I spotlight them because homeowners still plant them for ornamental purposes.
Japanese Blood Grass
(Imperata cylindrica ‘Rubra’). On first sight, Japanese Blood Grass is a cool, two-toned red and green grass. A lot of designers use it in modern home landscapes. Nurseries still sell it. It definitely has an alluring tall, wispy form. But resist the interesting color and gentle texture because once established, this grass runs happily and quickly, creating thick masses in almost any soil. I’ve often pulled it from the cracks of sidewalks when it’s slipped out from its parking strip boundaries. You’ll need to dig a wide, deep swath that goes on for several feet to get rid of it.
St. John’s Wort
(Hypericum perforatum). This is a voracious, evergreen perennial that spreads through rhizomes. I’ve tried to clear away this noxious plant more times than I can count in clients’ yards. Though it sports cheery, yellow flowers in June, it multiplies like crazy once established. What’s worse is it has stiff stems that are difficult to pull and roots that dig in to soil as if planted in cement.
One thing to note, however, is there are several cultivars that supposedly do not spread like the common species. One form you can pay me to plant is Hypericum x moserianum ‘Tricolor.’ That cultivar has awesome, three-tone foliage in green, white, and pink. It looks better out of bloom, since the flowers are also bright yellow, which in my opinion, clashes with the foliage.
(Iris foetidissima). With a mediocre, purplish flower, these irises are prized for their pods of reddish orange seeds. The seeds, which look like berries, add color and interest in the winter landscape, but when they ripen, they drop and roll in all directions. This leads to more irises, like dozens and dozens of them. To remove them is difficult. The foliage is strappy and often breaks off at the base, leaving the iris’s rhizome to create more leaves. Also, the root system digs in like a strong claw, making it difficult not to leave a broken piece of rhizome in the soil. Some people still like Stinking Iris because it will grow in deep shade, but I’d say you’re better off with nothing at all or plain, cedar mulch.
In my next post, I’ll talk about the invasive groundcovers you can’t pay me to plant. In the meantime, what are other grasses or perennials that have taken over your garden and drive you crazy?