Preparing for aggressive plants

Plant growth habits can sometimes come as a surprise. Plants may start to spread more than there is space for. How can unwanted spread be prevented? What should be mowed around, what blows in the wind, what needs competition, what will move downhill. With the numbers of native plants available in stores today, it would be impossible to list each one here but I will describe a few of the frequent offenders.

Ashy sunflower spreads into large colonies using underground runners. Since the plant is tall, it can over shadow smaller plants while also crowding them out underground. To keep this plant in check, plant it next to barriers like sidewalks or walls. Or be prepared to trench around it each year. Many sunflowers like plants in helianthus, silphium, and heliopsis have this characteristic of forming colonies by expanding their root system. Because of the spreading issue I like to add these plants after other plants have become established and staked out their own turf. The sunflowers also make nice prairie plantings when mixed in with other equally aggressive species.

Wild plum really wants to be a shrubbery. As the roots spread out, they form root sprouts that can come up over 10 feet away from the parent plant. Cutting off these sprouts often leads to even more sprouts coming up. Digging up the sprouts can damage the roots system and they often do not transplant successfully. Plant shrubs like plum, dogwood, hazelnut, willow, and sumac in areas where their root system will not be disturbed so they are less likely to produce suckers. Shrubby garden borders are great places for this type of plant.

Asters and goldenrods spread not only by spreading their roots but also by seeds. Aromatic aster is great at expanding its colony by roots while Drumund aster is better at spreading it’s seeds far and wide. Field goldenrod will send out long rope like roots and pop up a new plant every foot along it. When pulling up asters and goldenrods, make sure to dig down and get the whole root out. Seed spread can be limited by collecting the stalks before they ripen. Seeds need bare soil to germinate so minimizing bare soil near seedy plants can give them less spots to sprout. Asters and goldenrods look great in large clumps and are necessary for fall pollinators.

Joe pye makes a lot of seeds. Since it is such a tall plant, most gardeners can not work with the random volunteers of this giant plant all over the garden. Although seeds are important for birds, this is one of the plants that I dead head to prevent hours of work later weeding out the babies. After the flowers fade there is a window of time to get out in the garden and cut the seed heads off. Other plants that need their seeds clipped are rattlesnake master, and culvers roots. I like to plant these three together so I can maintain them together. Germinating seedlings should be pulled as soon as you can before they develop a deep tap root.

Blue lobelia makes thousands of dust like seeds that float on water. This means that baby blue lobelias will pop up anywhere downstream from their parent plant. The water dispersal technique is also used by many of the sedges. To prevent the spread, place these plants at the lowest point in the yard or block seed flow with a small dam. Planning for these water loving plants to move downstream can be used to your advantage by planting them upstream from where you want to planting to be densest.

Understanding how a plant will spread can be used to the gardener’s advantage when planning a garden. Plants that form colonies quickly can be given the amount of space they will need and use less plants to do it. Plants that are tall and aggressive can be paired with likeminded plants so they can keep each other in check. Very aggressive plants can be given firm borders, like sidewalks. Avoid using fertilizer on native plant beds to limit weedy growth. While this information might require some extra research, it is worth it in effort saved fighting the natural tendencies of a species with wanderlust.