Dividing Perennials
To lift a perennial with minimal root damage, begin digging at its drip line. The roots will generally extend that far, so digging there 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 outer 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 it.
In early spring, divide while the new growth is still low to the ground, so the handling of stems is not usually an issue. In summer, tie stems together before lifting the plant to avoid damaging them during the digging. In fall, cut plants back before digging them for division. Perennials can be divided at any time of the year if you give the plant appropriate care afterward. Divide 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 stay low, out of the sun and wind. After dividing, replant pieces that are, at most, 20 to 25 percent of the original clump. Smaller sections grow more vigorously and tend to produce stronger, longer-lasting blooms. Dividing a hosta, for example, into pieces with about seven growing points will yield the best results. Perennials multiply exponentially — one stem is likely to triple or quadruple itself each year. So if all you do is halve an overgrown clump this year, it will more than double in a season and need dividing again the next year. When you dig up a perennial, you will see that it fits into one of five basic root types: roots that form clumps or offsets, surface roots, underground running roots, taproots or woody roots. How you proceed depends on what root type your plant has.
Offsets: To divide a plant whose roots form offsets (small plants growing at the base of a larger one), snap the connection between any of the sections to obtain a piece with ample roots and three or more growing points (or “eyes”). Some denser clumps may have to be cut apart. Plants that form offsets include asters, coneflowers, hostas, tickseeds.
Surface roots: Some perennials have roots that run on or just below the surface of the soil. They form new crowns and roots when they reach open spaces or make
contact with the soil. If you cut between any of the stems as you would cut a piece of sod from a lawn, you will have a division with its own stems and roots. Plants with surface roots include bee balms, black-eyed Susan's, creeping sedums, creeping speedwells.
Taproots: Plants that have taproots can be divided by using a sharp knife to slice down the length of the root. Every piece that has at least one eye, some of the taproot, and a few side roots is a viable division. Plants that have taproots include balloon flowers, butterfly weeds, cushion spurges, Oriental poppies.
Underground running roots: Underground running roots can develop suckers as they grow beyond the shade of the mother clump. These suckers can be cut away from the main plant, or you can dig up the main plant and cut away any piece with an eye or sucker already forming. Plants with underground running roots include hardy geraniums, Japanese anemones, ostrich fern, plume poppies.
Woody roots: Woody perennials often form roots when stems rest on the ground or are buried by gradually accumulating mulch. Make a new plant by simply cutting
between the rooted stem and the mother plant. Plants that have woody roots include candytufts, euonymus, lavenders, sages.
From Fine Gardening 97, pp. 39-43 by Janet Macunovich
To lift a perennial with minimal root damage, begin digging at its drip line. The roots will generally extend that far, so digging there 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 outer 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 it.
In early spring, divide while the new growth is still low to the ground, so the handling of stems is not usually an issue. In summer, tie stems together before lifting the plant to avoid damaging them during the digging. In fall, cut plants back before digging them for division. Perennials can be divided at any time of the year if you give the plant appropriate care afterward. Divide 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 stay low, out of the sun and wind. After dividing, replant pieces that are, at most, 20 to 25 percent of the original clump. Smaller sections grow more vigorously and tend to produce stronger, longer-lasting blooms. Dividing a hosta, for example, into pieces with about seven growing points will yield the best results. Perennials multiply exponentially — one stem is likely to triple or quadruple itself each year. So if all you do is halve an overgrown clump this year, it will more than double in a season and need dividing again the next year. When you dig up a perennial, you will see that it fits into one of five basic root types: roots that form clumps or offsets, surface roots, underground running roots, taproots or woody roots. How you proceed depends on what root type your plant has.
Offsets: To divide a plant whose roots form offsets (small plants growing at the base of a larger one), snap the connection between any of the sections to obtain a piece with ample roots and three or more growing points (or “eyes”). Some denser clumps may have to be cut apart. Plants that form offsets include asters, coneflowers, hostas, tickseeds.
Surface roots: Some perennials have roots that run on or just below the surface of the soil. They form new crowns and roots when they reach open spaces or make
contact with the soil. If you cut between any of the stems as you would cut a piece of sod from a lawn, you will have a division with its own stems and roots. Plants with surface roots include bee balms, black-eyed Susan's, creeping sedums, creeping speedwells.
Taproots: Plants that have taproots can be divided by using a sharp knife to slice down the length of the root. Every piece that has at least one eye, some of the taproot, and a few side roots is a viable division. Plants that have taproots include balloon flowers, butterfly weeds, cushion spurges, Oriental poppies.
Underground running roots: Underground running roots can develop suckers as they grow beyond the shade of the mother clump. These suckers can be cut away from the main plant, or you can dig up the main plant and cut away any piece with an eye or sucker already forming. Plants with underground running roots include hardy geraniums, Japanese anemones, ostrich fern, plume poppies.
Woody roots: Woody perennials often form roots when stems rest on the ground or are buried by gradually accumulating mulch. Make a new plant by simply cutting
between the rooted stem and the mother plant. Plants that have woody roots include candytufts, euonymus, lavenders, sages.
From Fine Gardening 97, pp. 39-43 by Janet Macunovich