I am inclined to think that labeling plants as invasive is misleading. On one hand, we are supposed to be concerned that the jungle is being irreparably destroyed, but on the other hand, we are told to avoid a long list of vigorously growing plants. Do we want jungles or don’t we? Or do we only want them where we don’t live? I would like to suggest that the more useful question is, “How can you decide which plants are too invasive for your yard? Or, a more balanced way of putting it, “How do you decide what is an appropriate plant for your yard?” I have some criteria that might help you sort that out.
1. What sort of micro environments do you have? Everyone has areas with more sun, more shade, different soil composition, better water retention. A plant that is vigorous in a moist shady spot might be kept from unwanted reproduction by putting it in a location bordered by an area of full sun. My labrador violets thrive in the shade, filling in several square feet, but peters out where the sun is more regular.
2. Does it depend on watering? Some plants are more vigorous where they get multiple waterings a week, but other species like it dry and hot to do best. My mature maple trees spreads seeds over my whole acre, but they rarely grow in the area adjacent to the tree where there is no irrigation all summer long.
3. How hard is it to weed out unwanted plants? Some frustrating roots go down like monster tentacles, while others are like fists clenching the earth. Of course, this also depends on the soil quality or mulching. What is hard to pull in clay is not so much work in loose soil. However, I had some asters naturalizing a few years ago that made me shudder if I found a plant larger than a seedling anywhere. It was always a major excavation. Then, there are the pink evening primroses (Oenothera speciosa) whose roots seem to disappear into unknown regions of the ground, but I can’t be totally sorry when I see the delicate blooms again.
4. How large is your yard? Plants that might be a piece of cake to control on 1/4 acre can hide in a larger yard until they are of scarier proportions. My neighbor’s gigantic elm trees reseed prolifically, as vigorous plants often do. This is not a big deal when they are small, but when I don’t see them and their skinny saplings make it to even a foot tall, it takes quite an effort to dig them out.
5. How often do you see and tend an area of your yard? It is likely that you both notice and weed sections that are along more frequented paths. Plants won’t have as much of a chance to “take over.” Lamb’s ear can be kept very groomed if attended to enough, but if ignored for a while it gets quite wild, spreading by both root and seed.
6. Does a plant spread most by seed or by roots? If it is by seed, but the area has a mulch or ground cover, the seedlings may not get established or they will be easy to pull. If it is by roots, but the particular garden bed is bordered by roads or walkways, you won’t have to spend as much energy cutting them back. My mimosa tree is in the middle of the lawn. Seedlings are mowed out of existence on a regular basis, so I have no qualms about planting a few more. I planted a mound of mint in a small triangle bounded by asphalt on two sides and mature pine trees on the other. Sedum is a nice spreader that fills in along paths and in generally poor soil, but is easy to pull by the roots.
7. How much do you like to weed or deadhead? I actually find weeding to be relaxing. I like the feel of straightening the garden and the exertion of the process. I find deadheading to be more of a challenge, but manage a few select plant types that way because it is better than dealing with their roots. If you think weeding is a chore for the unfortunate and oppressed, you will want to be careful about growing plants that easily reseed. I have three clumps of chives just in view of the kitchen window that I dead head diligently. I had some before, growing in a more remote location, that nearly took over the front yard.
8. How much effort do you want to expend to coax a plant to grow well? This is the counterpoint to thinking certain plants are too vigorous. If a plant is not vigorous, it probably needs a different type of attention. It is often more expensive both to buy and to care for. Hybrid roses come to mind. In the last couple of years, I have cut back my hybrid rose population, but I still have a few to enjoy. I have alliums, for some earlier spring color in the rose bed, that need regular thinning.
9. How well do you like the flowers or fruit of the plant? There usually needs to be something about a plant to motivate you to grow it. Only you can decide if you like raspberries enough, for example, to be constantly battling it’s urge to spread canes like rabbits have babies. I love my hollyhocks and am quite willing to deal with all the volunteers in order to enjoy the tall stalks of large blooms along the fence each summer.
10. How thoroughly can you isolate a plant? I have already mentioned this idea in #6, when I talked about the mint. Isolation can also be achieved by planting next to a chicken yard, where they will peck away at any green or seedlings that venture over to their side of the fence. This is one of my methods for keeping comfrey down to dimensions that don’t overwhelm me.
If you like to garden, rather than just have a yard of rock and junipers, then you will probably decide to grow at least a few plants that have a degree of vigor that needs to be kept under control. I have some rules for myself that help a lot:
- When trying a plant of possible high vigor, only plant one to begin with.
- Be ruthless about weeding out volunteers when they are small.
- Have a clear idea of the boundaries of where you want it to grow.
- If your friends are interested in culling specimens, make it clear you will still be weeding on schedule and it is up to them to get it before then if they want it.
I think that what many gardeners really want is their own version of a well manicured jungle. Some like it more formal, but some enjoy more spontaneity in their plants. No matter what, there will always be a need for each of us to think about what grows well, in our particular environments, and how it can be maintained to our satisfaction. The plants are just trying to find a place to grow, because that is what they were designed to do. They are not out to get you.