Dr. Leonard Perry, Extension Professor
University of Vermont
Three questions you may ask this month include when to divide perennials, or to even know which need dividing, what to look for in buying plants, and whether to start a lawn from seed or sod.
The best time to divide most perennials is early in the spring, as soon as you can work the ground and as growth is beginning. Common exceptions are bearded iris (divide in late summer after bloom), and peonies (divide in fall). Some perennials may never need dividing, or only need it once every ten years or more. These include peonies, garden phlox, false indigo (Baptisia), and blue stars (Amsonia).
Perennials that grow quickly may need dividing every year or two. This includes perennials such as bee balm (Monarda), bearded iris, and Helen's flower (Helenium), or spreading plants such as Mugwort (Artemisia) and New York asters. The signs that it is time to divide are clumps with open centers, the presence of many thin stems, or few flowers.
You can divide plants using a sharp, square-tipped spade. Find a logical point in the plant, such as between clumps or stems. Slice down, dividing half or part of the plant off and lifting it out of the ground, leaving the rest. You may also dig the whole clump, divide it into smaller pieces with whatever tool works best for you (from trowels to saws to hatchets), and then replant or give away the divisions. Some prefer dividing a clump using two spading forks, placed in the clump back to back, and used to pry apart divisions.
Since it takes just as many sore muscles to get good plants in the ground as poor ones, it makes sense to be picky when buying flowering plants. Margaret Hagen, from the University of New Hampshire, recommends buying plants that are almost as wide as they are tall. If you have a choice between small plants, and tall ones with roots growing out of the bottom pot holes, choose the smaller ones. Plants that have grown just enough to fill the soil area in the pot are ideal.
Young, actively growing plants can be transplanted with little damage to their root systems. Those that are root-bound don't make the transition as well, and may never root out into the soil once planted. Don't be afraid to turn pots over, holding your hand on the soil, and slip plants out to inspect their roots. Healthy roots should be white, and fibrous, and not tightly circling the pot.
It is also best to buy flowering plants just coming into bloom. This way you can guarantee the color you see on the tag, or want, is the color of the bloom. Yet if they are just starting to bloom, you'll still get good growth and rooting once planted.
If you are renovating, or even starting, a lawn, consider the advantages to both seed and sod. Sod is simply a lawn that has been grown by professionals under ideal conditions, then cut into strips you can lay down for an immediate effect.
The biggest problem with getting a lawn to establish from sod is not preparing the soil well, just as you would for a seedbed. This includes tilling and raking out stones, incorporating plenty of organic matter, and adding lime or fertilizer according to a soil test from your local Extension office.
Dr. Lois Berg Stack, from the University of Maine, gives four factors that might affect your choice of seed or sod. First, because most available sod is Kentucky bluegrass, you'll have to start from seed if you want a different species. For instance, you may want a fescue for shady or dry sites. A mixture of grass types, especially on a variable landscape, may result in less maintenance over the long term.
Second, it can be challenging to establish a uniform lawn from seed on a slope subject to erosion. Sod might be an easier and more successful choice there. Sod is also a good choice if you need to walk on an area soon after put down. You will have to stay off a seeded lawn for many weeks while it establishes.
Third, high quality sod contains no weeds, and the grass root systems are already quite tight and competitive with any weed seeds that might be in the soil. This helps reduce, or eliminates, the need for weed control while the lawn gets established. This means fewer or no herbicides, and less potential harm to the environment.
Finally, seeding a lawn is most successful in either spring or fall,
but sod can be successfully installed anytime during the growing season.
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