Timely tips for transplanting success
Perennials are best divided before they become decrepit looking or monstrous like many have this year. If a plant is looking good, divide it at the end of its blossoming season. Summer heat and lack of rainfall are hard on plants, so the day before you dig out the plant, water it down well along with the spot where it will be planted.
Before you dig out the plant, cut the foliage back to about half. This way a smaller root system won't have to support lots of foliage in the heat of the sun. To make the transplant more manageable, take twine or string and tie it around the part of the plant that you want to remove to transplant. To lift a perennial with minimal root damage, begin digging at its drip line. The roots generally extend out that far. Digging at the drip line lets you lift the plant with most of its roots intact. Dig a trench around the clump, cleanly severing any roots, then cut at an angle down and under the clump from various points around the edge until you can lever the plant out of the hole. For large heavy plants, you may have to first dig the trench, then slice straight down through the center of the plant as if it was a pie, halving or quartering the clump before undercutting and lifting.
Perennials can be divided any time of the year if you give the plant appropriate care afterward. However, the best time to divide is when the soil is warmer than the air for at least part of every 24 hour period. That's just before peak daffodil season in spring and in early fall right after the nights become cool. These conditions will allow the roots of the division to grow, while the tops will grow slower staying low, out of the sun and wind. Fall is a good time to divide because the plant tops are not growing and it puts all its effort into setting new roots before winter freeze up.
Dig the perennial and get it into its new home as quickly as possible so the roots don't dry out. Do this in the evening when the sun is going down and it is cooling off rather than in the heat of the afternoon sun. Place the division into a hole that is at least as wide as its roots when spread out. Don't turn a root tip up rather than down or curl it back and around on itself to fit into an undersized hole. This defeats the plant's natural regrowth mechanism. Root tip growth is regulated by chemicals which flow down from the tips of leafy stems to the roots. As in all flows, gravity is involved, so if you plant a root tip up when it was down, the normal flow is interrupted. At least temporarily, that root tip will not grow as vigorously as it could.
Before you place the perennial in its new hole, put some compost in the bottom of the hole. It is a good idea to add a root stimulator (which has a high middle number-Phosphate) to the water you use to encourage root growth. Place the plant in its new home, fill the hole halfway with soil and water well. This way the water soaks in and doesn't evaporate or roll off the soil's surface. Then fill the hole the rest of the way with soil, firm it well and add more water. This will get rid of any air pockets around the roots. Mulch around the plant, keeping the mulch a few inches from the plant's base.
Remember also the hole that you dug to take out this perennial. You need to replenish the hole with soil, compost or organic matter. If you removed a bushel full of perennials, then you should put a bushel full of compost back into that site to renew the soil. If the hole is left, the bed will settle, putting the remaining plants at a disadvantage in terms of drainage and air circulation.
Even plants which love full-sun will benefit from a shade shelter for a week or two after they are transplanted. Insert a few stakes in the soil on the west side of the plant to protect it from the hottest sun of the day. Tie landscape fabric or an old sheet to the stakes to make a screen. Finally, check your plant each day, and if it looks wilted in the morning or late evening, give it some water. It may need water daily for a few days after transplanting.
Kyle Schulz is a Wadena County Master Gardener from Sebeka, and the regular gardening columnist for the Wadena Pioneer Journal.