By Mel Bellar
Last month, I explored the idea of volunteers in the garden. “Volunteers” being the polite term we use for seedlings that are welcome, somewhat welcome or at least require a second’s thought before pulling. Today I want to talk about the more insidious and less random root spreaders. Plants that spread via rhizomes or stolons are often considered to be thugs and some serious (maybe OCD is a better characterization) gardeners won’t even use them in their gardens. However, I am not one of those gardeners and often welcome a good spreader in the garden, especially if I want a workhorse to cover a lot of area quickly.
In an attempt to be a little more knowledgeable about my subject, I set off to do a little research and, after very little time, my head was about to explode. The difference between rhizomes and stolons gets really technical! There are different types of each and some stolons grow below of the surface and some roots producing new plants are not rhizomes and some plants spread through rhizomes AND stolons. I think I will stick with the common layperson view that rhizomes are below the ground and stolons above the ground (pretty much anyway). Rhizomes are roots (or root stems) and stolons are stems. They both have nodes and these nodes often produce new little roots and subsequently new plants.
Plants that spread through rhizomes should be approached with much caution. There is great range in the vigor and threat of these plants. Japanese Knotweed is the poster child of horrible invasive plants that spread primarily through rhizomes. As a gardener, rather than an environmentalist, I consider Bishop’s Weed (also known as goutweed, ground elder, herb gerard, gout wort and snow-in-the-mountain) to be the devil incarnate. The botanical name of the this plant is Aegopodium podagraria and the list above (and there are more that I left out) shows why gardening professionals use botanical names, not to be snooty, but to be clear about what we are talking about. This plant is nearly impossible to get rid of after it once takes hold in a garden. I live in fear of having it introduced into my garden and will not take divisions or gift plants from anyone who I even suspect of having Bishop’s Weed in their garden. Furthermore, I would not buy a property with this evil plant on any adjacent property because I know that its evil would eventually make its way onto my property.
Now for a look at aggressive garden plants that require caution but can be useful. Gooseneck loosestrife (Lysimachia clethroides) is a very attractive plant that can be useful as a groundcover for large areas in the sun or as an ornamental perennial as long as you don’t put it where it can get tangled up with less thuggish plants. It has nice flowers for several weeks in July/August and good fall color. Obedient Plant/False Dragonhead (Physostegia virginiana) is a native plant that has erect lavender flowers that blooms late in season. It is pretty manageable but will still cover some territory. Helianthus ‘Lemon Queen’ is another summer perennial I like that adds a lot of color (if you like yellow) and some height to the garden and spreads through rhizomes fairly aggressively. Here are some others I like that are a little less aggressive and useful (if this were online and I were famous I know I would get SO MUCH pushback on some of this!): Sun: regular garden phlox (Phlox paniculata), queen of the prairie (Filipendula rubra), evening primrose (Oenothera), various fleece flowers (persicarias bistorta and amplexicaulis are 2 I love), geranium maculatum ‘Cappuccino’). One of my favorite rhizomatous plants is Astilbe chinensis ‘Pumila’ (sorry, no common name) which will do well in sun or shade, blooms late and stays close to ground. There are, of course, many, many more in every category.
Shade: There are many shade plants that spread via rhizomes as well. Here are some that I use and like (no botanical names!) ostrich ferns, sensitive ferns, Canadian ginger, European ginger, foamflower, golden ragwort, wild geranium (especially the cappuccino variety). Again this is just a smidgen of the list.
There are a few shrubs that spread readily through rhizomes. Annabelle hydrangea will spread to cover quite an area if uncontrolled but I love them and use them constantly. Sorbaria sorbifolia (misleading common name is false spirea) is one that I would never put in the ground and only use in pots. The SEM variety is very beautiful in a pot. Bush honeysuckle (Diervilla lonicera) is another great native ground covering shrub that runs rampant via rhizomes.
Last but not least, stoloniferous plants. Luckily there are not as many and I don’t use/love that many of them. Here are a few perennials and ground covers that I like: strawberries (numerous varieties), ajuga and thyme and my favorite big root geraniums (Geranium macrorrhizum). The big root geranium is the best ground cover I know in that it looks good in all seasons (it is evergreen), the deer don’t eat it and it has a nice fragrance. The bottom line regarding volunteers and spreaders is that you need to know your plants before you put them in the ground. Ask the nursery or the gifter about the plant before you commit a spot in your garden to it. I promise something less geeky next month.~
Mel Bellar is the owner of Zone4 Landscapes and a passionate Andes gardener.