How to Identify Perennials You Can’t Divide
By The National Gardening Association, Bob Beckstrom, Karan Davis Cutler, Kathleen Fisher, Phillip Giroux, Judy Glattstein, Mike MacCaskey, Bill Marken, Charlie Nardozzi, Sally Roth, Marcia Tatroe, Lance Walheim, and Ann Whitman from Gardening All-in-One For Dummies
Gardeners know that producing more plants is the main reason to divide your perennials, but not all perennials can be divided. Division works best on perennials that grow into colonies — groups where each new plant develops its own set of roots and leaves. Similarly, most bulbs reproduce by forming clusters of new bulbs which you can divide in exactly the same way that you divide colony-forming perennials.
Some types of perennials reproduce themselves so quickly that they can overrun the whole flower bed if you don’t intervene. Whenever you feel the need to restore order, dig up these miscreants, put a piece of them back where you originally planted them, and give the remaining pieces away.
A young perennial starts out with only one tuft of leaves and one set of roots. Many perennials reproduce themselves by sending out a length of root or stem from which a whole new plant grows. Eventually, a cluster of loosely connected but separate plants forms. The process of pulling clumps of perennials apart to create new ones is called dividing. Each piece then grows into a new clump that you can divide, and so on.
A few perennials die out in the center of their clumps as they spread, creating a noticeable bald spot. Instead of contemplating some sort of a floral toupee, you can easily correct the problem by digging up the whole plant and dividing it.
Perennials with a single, large taproot and those with multiple stems arising from a single crown don’t like to be divided. The following perennials don’t tolerate division well:
Monkshood (Aconitum napellus)
Butterfly flower (Asclepias tuberosa)
Basket-of-gold (Aurinia saxatilis)
Blue wild indigo (Baptisia australis)
Pinks (Dianthus)
Bleeding heart (Dicentra spectabilis)
Gas plant (Dictamnus albus)
Globe thistle (Echinops exaltatus)
Baby’s breath (Gypsophila paniculata)
Candytuft (Iberis sempervirens)
Sea lavender (Limonium latifolium)
Blue flax (Linum perenne)
Lupine (Lupinus)
Oriental poppy (Papaver orientale)
Balloon flower (Platycodon grandiflorus)
False lupine (Thermopsis carolinian)
Growing perennials from cuttings involves creating a new plant from a stem that starts out with no roots at all. If you’ve ever stuck a stem of ivy in a glass of water and watched it grow roots, you already have some idea how this technique works. Not all perennials can grow from cuttings. Use the cutting method for perennials that don’t tolerate division.
Gardening Glossary
annuals
Plants that complete their entire life cycle within one growing season. The plant germinates from seed, grows and blooms, and then produces seed and dies.
Gardening Glossary
biennials
A plant that take two growing seasons to complete its life cycle. It germinates and grows leaves and stems in the first year; produces flowers and fruit (seed) in the second, and then dies.
Gardening Glossary
bolt
When a plant flowers or produces seed prematurely.
Gardening Glossary
cold frame
A wooden or concrete block box in which you can grow plants or hold dormant during the cold winter months.
Gardening Glossary
cole crops
A family of vegetables, including broccoli, cabbage, cauliflower, kale, and Brussels sprouts. They thrive in cooler weather.
Gardening Glossary
complete fertilizer
Any fertilizer that contains all three of the primary nutrients, N-P-K (nitrogen, phosphorus, potassium). Phrase is based on regulations governing the fertilizer industry. Does not mean that the fertilizer literally contains everything a plant needs to thrive.
Gardening Glossary
deadheading
The practice of pinching or cutting off spent flowers
Gardening Glossary
evaporative-pad humidifier
A humidifier in which fans blow across a moisture-laden pad that sits in a reservoir of water.
Gardening Glossary
harden off
The process of acclimating plants grown indoors gradually to the brighter light and cooler temperatures of the outside world.
Gardening Glossary
hardiness
The ability of a plant to survive is called its hardiness.
Gardening Glossary
humus
A stable end product of organic-matter decomposition that's believed to increase microbial activity in soil, improve soil structure, and enhance the root development of plants.
Gardening Glossary
Bacillus thuringiensis Bt
An effective bacteria that attacks only the larvae of caterpillar family insects. It is safe to other insects, animals, and humans.
Gardening Glossary
macronutrients
Mineral nutrients that plants need in the largest quantities: nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur.
Gardening Glossary
mulch
Organic or inorganic material placed over the surface of soil, usually directly over the root zone of growing plants. Used to conserve moisture, kill weed seedlings, modify soil temperature, provide attractive covering to garden beds.
Gardening Glossary
organic matter
Once-living stuff like compost, sawdust, animal manure, ground bark, grass clippings, and leaf mold (composted tree leaves). Used to enrich soil and improve soil texture.
Gardening Glossary
perennials
Any plant with a life cycle of three or more years. Herbaceous (non-woody) perennials include flowering plants and herbs, mainly. Woody perennials include trees and shrubs. Longevity depends on the plant and growing conditions.
Gardening Glossary
pH
The measure of soil's acidity. Soil with low pH means it's too acidic; soil with high pH means it's alkaline. Most plants grow best in soil with a pH value between 6.5 and 7.2. Neutral soils measure 7.
Gardening Glossary
photosynthesis
The process through which plants take nutrients from the air and from the water in the soil to produce sugars that fuels the plant's growth.
Gardening Glossary
primary nutrients
Nitrogen, phosphorous, and potassium are the three nutrients plants need in the largest quantities.
Gardening Glossary
root crops
Plants with edible underground roots such as onions, carrots, beets, potatoes, turnips. Most root crops are cold-weather crops.
Gardening Glossary
self-blanching
A type of cauliflower with leaves that naturally curl over the head and exclude light. Requires cool temperatures for leaves to curl effectively.
Gardening Glossary
sets
Small onion bulbs, about 1/2-inch wide, that were started from seed the previous year. Grow onion sets with the pointy end up.
Gardening Glossary
side-dressing
The act of adding a small amount of fertilizer around or "on the side" of plants after they're growing.
Gardening Glossary
succession planting
Planting small, 2-to-4-foot patches of plants every two weeks throughout the growing season so that you can harvest a crop over an extended period of time.
Gardening Glossary
thinning
The act of cutting the least robust seedlings in your garden to give the healthier plants more room to grow.
Gardening Glossary
vining crops
Crops that grow on vines, such as cucumbers, melons, pumpkins, and winter squash. They usually require support (staking, trellising, etc.) to keep them off the ground.
