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Even though perennials provide us with blooms year after year, and are often carefree plants, that doesn't mean that you can just plant them and totally forget them. Most perennials grow larger every year, usually by spreading through underground stems or roots, and may need to be periodically divided. This is one of the rewarding aspects of perennial gardening, when your
perennials are going to benefit from being divided. The first time
or two dividing perennials you may be unsure of what you're doing. After you see most perennials have natural divisions and how easy it is to increase your garden, you will be hooked.
The three main reasons for dividing perennials are to
control the size of the plants,
help rejuvenate them,
- yellowing or hollow in the middle
- flower performance has declined
- soil nutrients have been exhausted
- weeds have infested the clumps
And the #1 reason - to increase their number.
Dividing will rejuvenate old plants, keeping them vigorous and bloomin.
Some perennials
can be simply pulled apart with your hands; others may
need to be sliced with a knife, spade or even cut with a saw. Almost
all
varieties of perennials can be divided, but there are a few that should
be propagated from seed, tip cutting or root cutting, How you divide a
perennial
will depend on the type of root system.
When dividing
perennials, timing and technique are important, but many
gardeners are known to break the rules when dividing perennials,
experiencing
relatively few problems. Nevertheless, spend a little time before
you start and decide where the divisions are going and take the
opportunity
to amend the soil.
WHEN
It is best to
divide perennials on cloudy, overcast days. Hot sunny day
can cause the plants to dry out plus you sweat it out.
In general, it
is best to divide spring and summer blooming perennials
in the fall, and fall bloomers in spring “if it blooms early, divide
late
and if it blooms late, divide early”. By dividing the plant when it is
not
flowering, the plant's energy can go to root and leaf growth. Many
perennials
can be satisfactorily divided in either early spring or early fall.
Spring division
should occur as new growth is emerging. New leaves and
shoots won't suffer as much damage as full grown leaves and stems plus
it
is easier to identify natural divisions. Some gardeners always
divide
in the spring because it also allows the plants an entire growing
season
to recover before the onset of winter (especially in northern
climates).
Most spring and summer flowering perennials divided in the
early
spring will flower the same year, possibly blooming a little later than
usual.
If you divide in
the spring, allow enough time for roots to settle in
before hot weather. If planting in late summer or fall prune the
foliage to stimulate growth, and have your new plants in the ground at
least 30 to 45 days before the first frost.
Most perennials
should be divided every three to five years. Some
perennials such as chrysanthemums and asters may need to be divided
every year or two. Bleeding hearts and peonies may never need to be
divided unless you want
to increase your stock.
HOW
Water plants to
be divided thoroughly a day or two before you plan to
divide them. To repeat myself, prepare and amend the area that you plan
to put
your new divisions before you lift the parent plant.
If the plant has
already bloomed or there is much foliage, prune to 6
inches from the ground to ease division and to reduce moisture loss.
Use a spading or
garden fork (or if you must, a sharp pointed shovel)
to
dig down deep on all four sides of the plant, at least 4 to 6 inches
away
from the plant. Pry underneath with your fork and lift the whole clump
to
be divided. If the dirt ball is very large, use the fork to loosen the
dirt
before lifting it.
When digging try
not to cut the roots especially the ones with tubers
(like daylilies, peonies, iris and hosta) or fleshy roots (like poppy,
balloonflower and bleeding heart).
You also have a
second option when dividing perennials. Use a sharp
shovel to slice down and remove sections of the plant, leaving part of
it intact. Generally it's better to dig the whole clump and carefully
split it into
sections.
SEPARATE THE PLANT
The basics of
dividing are simple - shake or hose off loose soil and
remove dead leaves, stems and roots. This will help loosen tangled root
balls and make it easier to see any natural points where the clump can
be easily separated. After each division split look for the next
natural division first. Certain perennials will almost fall a part,
others will need more effort, possibly a hatchet. Every new division
should have both green shoots as well as roots.
Perennials can
be divided in to small pieces that will take time to
reestablish or leave 3 to 4 growing points in each division for plants
that could bloom during the next cycle. Plants with fibrous root
systems can simply be cut into pieces with a sharp tool and reset. For
plants with rhizomes or tubers, use a sharp knife to cut the root
system apart. For plants with hard, woody root systems, it may be
necessary to use a hatchet or a very sharp spade.
Perennials have
different types of root systems. Each of these needs to
be treated a bit differently.
Spreading root
systems have
slender matted roots that originate
from many locations with no distinct pattern. Plants with spreading
root
systems include asters, bee balm, lambs ear, purple cornflowers and
many
other common perennials. These can crowd out their centers. Some can be
invasive unless divided frequently. They can usually can be pulled
apart
by hand, or cut apart with shears or knife.
Large, vigorous
plants with thickly intertwined roots may need forceful
separation. Put two forks back to back in the center of the plant and
use them to pry the pieces apart. Discard the center of the clump if it
is weaker than the outside edges.
Clumping root
systems
originate from a central clump with
multiple growing points. This group includes astilbes, hostas,
daylilies and many
ornamental grasses.
It is often
necessary to cut through the crowns (the central growing
area between the roots and the leaves or stems of the plant) with a
heavy, sharp knife. Keep at least one developing eye or bud with each
division. If larger plants are wanted, make it several eyes.
Rhizomes are stems that grow
horizontally at or above the soil
level. Bearded irises are the most common perennial with this type of
root system. Divide irises any time, from a month after flowering until
early fall.
Cut and discard
the rhizome sections that are one year or older. Also,
inspect rhizomes for disease and insect damage. Damaged rhizomes should
be trimmed and treated, or discarded if too badly damaged.
Iris divisions
should retain a few inches of rhizome and one fan of
leaves, trimmed back halfway. Replant with the top of the rhizome just
showing above soil level.
Tuberous roots
Tubers should be cut apart with a sharp knife. Every
division must have a piece of the original stem and a growth bud
attached. After
division they can either be replanted or stored for spring planting.
Dahlias
are an example of perennials with tuberous roots.
Plants that have
very tough, vigorous root systems (agapanthus, red-hot
pokers and ornamental grasses) may have to be divided with a shovel,
saw or
ax.
PLANTING
Never allow
divisions to dry out. Keep a pail of water nearby to
moisten divisions until they are planted. Trim all broken or damaged
roots with
a sharp knife, scissors or pruners before replanting, new roots usually
grow from clean cut ends.
Plant the
divided sections immediately in the garden or in containers.
If planting in containers use potting soil; the soil from your garden
becomes hard and compact, and plants suffer from a lack of oxygen at
their roots
Replant divisions at the same depth they were originally. Firm soil
around
the roots to eliminate air pockets. Water well after planting and for
most
plants, at least one inch of water per week for the first few months,
if
necessary.
Northern
fall divided perennials should be mulched the first winter to
prevent heaving caused by alternating shallow freezing and thawing of
the
soil. The best winter mulch is loose and open like pine straw.
If you
can't get everything planted right away, throw some dirt
on the roots and then water well, creating a slurry of mud. The mud
coats and protects the roots as well as the necessary mycorrhizae and
other fungi
attached to the roots.
PERENNIALS THAT
DO NOT LIKE DIVIDING
Avoided if
possible - baby's breath (Gypsophila), bleeding heart
(Dicentra), butterfly weed (Asclepias), columbines (Aquilegia), coneflowers (Echinacea), euphorbias, false indigo (Baptisia), gas plant (Dictamnus albus),
Japanese anemones, lupine (Lupinus), monkshood (Aconitum), peony (Paeonia), and
poppy (Papaver). If you must divide, try peonies in the fall, Oriental
Poppies in mid summer when they are dormant and true Lilies in mid to late
fall.
Lenten and Christmas roses (Helleborus) are very difficult to move when
more than a few years old. Look for tiny seedlings around the base.
Lavender cotton (Santolina chamaecyparrus) and several other perennials
are actually small woody shrubs and should not be divided. These include perennial candytuft (Iberis sempervirens), lavender, rosemary, southernwood
(Artemesia abrotanum), and several other artemesias. These plants often have
rooted layers (branches that have developed roots while touching the soil).
The layers can be cut off the parent plant, dug up and replanted as though
they were divisions.
Extra Tips
Easy to divide and multiply perennials are, ajuga, beebalm, campanula,
coral bells, coreopsis, daisy, daylily, hosta, iris, lily of the
valley, mallowsundrops, phlox, pinks, sedum and yarrow. Spring is the
best time for dividing most ornamental grasses, and especially the fall-flowering types such as Maiden Grass
(Miscanthus)and Fountain Grass (Pennisetum).
Chrysanthemum divide hardy mums in spring before the shoots
begin to lengthen. Healthiest shoots are taken from the outside.
Remember to pinch the new shoots back once or twice to force the new
growth into a bushy form.
Daylilies (Hemerocallis) can be
divided any time, but spring is
best. Daylilies may need to be divided every 5-6 years.
Hosta divisions are best done in the spring, but early fall
division should be successful. If dividing in spring, do it just after
the new growth pokes through the soil. Ideally, each clump should
consist of at least three healthy shoots.
Iris should be divided right after flowering. When dividing,
cut the foliage height by half. Remove any tubers that are soft or
rotten. A single fan of leaves can be planted, but for a flowering clump, set three fans in a triangle 10-12 inches apart with the fans facing the same direction. The shoulder (or top) of the rhizome should be only slightly covered with soil when it is planted. Well drained soil is very important.
Lily of the Valley plants are easily divided in spring or fall.
Keep the strongest pips (divisions) and discard the oldest ones.
Peonies can sometimes be left 10-12 years without dividing. They
are best divided and transplanted in the fall. Select divisions with
3-5 eyes (the pink buds on top of the clump) and discard the old woody sections.
Enrich the soil with peat moss or compost and replant the clumps so that the
eyes are about 1 to 1.5 inches below the soil surface (depending on your
Zone).
Phlox can be divided in spring or fall, but autumn is better. Tall
varieties may need to be divided every 2-3 years. Keep 3-5 stemmed sections
and discard the woody centers. Remember to plant them in a sunny location
with good air circulation. This will help prevent powdery mildew disease.
If phlox is dug in late summer or early fall, a circle of new plants may
arise next spring from the root tips that remain, but less likely with
spring transplanting.
Click on WHEN AND HOW
TO DIVIDE SOME PERENNIALS for more tips.
Fertilizing perennials: do not fertilize less
than 60 days
before first frost. Short acting liquid fertilizers may be applied a
little later
in the season. Lime and super phosphate can be added any time.
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