Some plants spread or reproduce aggressively in our gardens by rhizomes (roots).
These sometimes “bad actors” in our gardens are often not labeled as such. Initially we envision their beautiful flowers gracing our garden in healthy substantial clumps. Only later do we learn, after the damage is done, that we have a resident thug in our garden.
It may be several years before we understand that their fecundity of growth is without end and will gobble up everything in the surrounding area, eventually usurping the entire garden.
By this time, the plants may be difficult to confine or eradicate. As the old adage goes: “The first year it sleeps, the second year it creeps, and the third year it leaps.”
Mint is the first plant that comes to mind when topic of spreading plants is mentioned. It quickly and aggressively spreads by underground rhizomes, a small piece capable of recolonizing a clean area.
A well-watered mint may achieve a 2-foot spread over the course of a summer. As the adage describes, a plant strengthens and gains potential for spreading as it gains root area and top growth.
Not all spreaders behave the same way in all circumstances. When established, in coastal areas the stunning Matilija poppy (Romneya coulteri) can send out strong shoots several feet from the original mother plant each year, and quickly gains momentum.
In hot inland areas with limited irrigation, it grows slowly, may only enlarge by 6 inches a year, and is easily controlled. Control is key with these plants, many of which have beautiful flowers and many redeeming traits. If growth is cut back on a schedule, they can be good citizens in our gardens.
These aggressively reproducing plants can both be a problem or a blessing in our gardens depending on the situation and circumstances.
Mint, when confined by concrete, becomes a wonderful scented groundcover, with profuse flowers that bees, butterflies and beneficial insects eagerly seek out. The spreading ornamental oreganos make a floriferous low groundcover that looks handsome all year. Some grow well under trees in shade, which are difficult areas to grow other plants.
The important thing is to be aware of how these plants grow and site them accordingly so their best qualities can be utilized and their propensity to spread is contained. Mulched soil may make it easier to remove them.
The list below should be useful for this purpose:
Mexican evening primrose (Oenothera speciosa syn. berlandieri). Native to the southwest and Texas areas, this lovely poppy-like plant with pink flowers grows to 1 foot tall. It graces spring gardens but goes dormant in July. It spreads quickly by thin runners that are hard to remove. They’re great under drought-resistant shrubs.
Hairy sunflower (Helianthis hirsutus). An absolutely beautiful perennial sunflower, it grows to 5 feet tall and spreads over time. It dies to the ground and is easy to cut back in winter. It can tolerate some shade.
Giant sunflower (Helianthus angustifolius). It has big, coarse stems that grow to 9 feet tall. It has small but very showy flowers. It comes late and is hard to cut back. However, it dies back to the ground. Great in very large gardens or vineyard edges.