Some of my favorite groundcovers are periwinkle, thyme, sedum, and veronica. I know that sounds quite broad, particularly when veronica offers almost 500 species alone, but it's intended to suggest that there are groundcovers for all landscapes and regions in all sizes, shapes, and colors. I use periwinkle, or vinca minor, to smother weeds at the base of my irises; I love the little violet flowers and almost evergreen foliage. Thymus lanuginosus, or woolly thyme, and sedum anglicum surround the flagstones leading into my backyard; they help keep the slight slope from eroding, require little water, and look spectacular, especially when their little flowers bloom. Veronica pectinata, or blue woolly speedwell, is a new addition along the sloped edges of my stone patio.
As most of these groundcovers grow, they'll add little roots along their expanding branches. Where a small stem, branch, or leaf touches the soil a root may develop. This helps the plant gain a larger foothold for increased growth and nutrient absorption.
By lifting up on the edge of an established plant and pulling back the branches and leaves you'll get to the spot where young roots have started anchoring new growth to the soil. With very little effort you can dig up a section of the plant and transplant it to a new location. The mother plant will continue to grow and send out new branches to cover the bare spot. The transplanted piece will begin growing soon because it already has roots in place. This saves time from taking a clipping and waiting for roots to develop.
I begin by determining what plant should be added to which new spot. In my stone walkway I intersperse thyme and sedum, but along the edge of my patio I'm focusing on Veronica pectinata, a plant first given me by my good friend Della. She has it covering a large, steep slope in her landscape where it presents a beautiful sea of green. The section I'm planting is smaller and not as steep, but I want the same seemless coverage the plant provides.
A mother plant is selected, one that is healthy and large enough to handle losing some of its growth. I lift up on the edges until I find a spot that is full of healthy, young growth and abundant roots.
With a trowel I'll dig under the plant to access some of the older roots too and lift out a section of the plant, with soil included. With my other hand I'll gently separate the main plant from the removed piece. The branches and leaves of groundcovers often intertwine and you have to be careful not to crudely rip apart tender foliage.
By selectively removing pieces of strong plants and moving them to new spots, an even larger area can be covered. Both old plants and new plants will grow and spread and will eventually meet. The process can be continued indefinitely. I'm patiently waiting for my patio border to fill in and expect the entire area to be covered within two years.
I tend to do much of my propagating in late summer. The heat and stress of the summer peak is over and the mother plants are as strong as they'll be. I can also see the bare spots that still need to be filled. Setting new transplants in place gives all of them opportunity to grow roots before winter sets in. Depending on their hardiness, I know I'll lose some over the cold months but when spring comes I'll have an increased number of plants beginning to grow. By the end of next summer, some of the transplants will be big enough to offer themselves for more propagation.
As with all plants, groundcovers do best when planted in the proper location. Once the right plant is in the right spot it will grow strong. Take advantage of that and let it spread with a little of your propagating knowledge.