Roots on Roots
By BETSY STRAUCH
HAVE YOU EVER TRIED to get all the bindweed or
goutweed—or mint—out of your herb bed, only to discover new plants
flourishing a few weeks later? All that hoeing and digging you did
just chopped up the roots and rhizomes, and each bit turned into a
new plant. Aggravating as this tendency can be when you’re trying
to get rid of an unwanted plant, it can be turned to your advantage
to multiply desirable herbs.
Herbs that have fleshy roots or that tend to produce suckers are
good candidates for this kind of propagation. They include
bayberry, sassafras, horehound, bee balm, butterfly weed, purple
coneflower, violets, salvias, sea holly, perennial mullein,
Oriental poppies, and sea lavender. Root cuttings can give you more
plants than division, and the technique is easier than stem
cuttings, at least for many herbs. Vegetative propagation using
root cuttings is an especially useful method for increasing prized
cultivars or hybrids that don’t come true from seed.
Taking cuttings
Comfrey is a fine choice for your first attempt at this
technique, as the root pieces readily form roots and tops. For the
greatest likelihood of success, take root cuttings early this
spring before the plant has put out a lot of new top growth or or
early next fall after flowering is done. When the plant is putting
its energy into flower production, stem buds form less readily in
the root tissue. Even so, most of the root cuttings of comfrey that
I took late last spring when the plant was several feet tall showed
new top growth within five weeks.
Taking cuttings from large roots takes less dexterity and
fussing than with stem cuttings. You can dig up an established
comfrey plant (or other herb) and cut off roots with pruning shears
or a sharp knife, or leave the plant in the ground and just dig up
soil next to it that contains some of the larger roots.
You are after the fleshy roots 1/4 to 1/2 inch thick, not the
fine feeder roots. Cut these thick roots into 2-inch lengths and
gather several together with a rubber band to keep them oriented in
the same way that they grew. You can cut the tops of the pieces
straight across and the bottoms diagonally to help you recognize
which end is which, but the plant needs no such reminders. The end
of the root piece that was originally uppermost will sprout a stem
and leaves, and the opposite end will sprout roots, no matter how
it is planted, but orienting the piece correctly enables it to
expend the least amount of energy in sprouting.
Herbs that have fleshy roots or that tend to produce
suckers are good candidates for this kind of
propagation.
Into a mix
Weeds obviously root perfectly well in ordinary garden soil, but
the ideal rooting medium for more challenging plants combines good
drainage with good moisture-holding ability—qualities that may not
be present in your garden soil. Equal parts of peat and sand,
vermiculite and perlite, or peat and perlite are commonly used
soilless potting media that drain well yet hold moisture. I have
tried them all, with varying degrees of success.
If you want to root a lot of cuttings at once, select a flat
that is a little deeper than they are tall. If you are rooting only
a few large cuttings, you may wish to place them in individual
pots. This will also save one step in transplanting after they
root.
You may place roots in the container vertically, diagonally, or
horizontally. If you lay them horizontally, you won’t need to worry
about which end is which, and you can use a shallower container
than you’d need if you oriented the roots diagonally or vertically.
On the other hand, horizontal cuttings occupy more surface area,
which may be a consideration if you have very limited space for
this project and want lots of new plants.
Fill the container to within 1/2 to 3/4 inch of the top with
dampened rooting medium. Place the cuttings in neat rows in
whichever orientation you choose. You don’t need to poke holes for
the vertical and diagonal pieces unless they are quite thin, nor do
you need to use a rooting hormone. Fill the rest of the container
with dampened medium, covering the root pieces.
Vegetative propagation using root cuttings is an
especially useful method for increasing prized cultivars or hybrids
that don’t come true from seed.
Time to grow
If you take cuttings in the fall, you may place the filled flat
in a cold frame or cool porch for the winter. Don’t expect to see
any top growth until spring. Alternatively, you may bring the flat
indoors and keep it in a warm spot or on a heating cable. Top
growth may begin in a few weeks, and you will then need to
transplant the cuttings to pots and keep them indoors until spring.
Keeping them outside is a lot less bother.
Flats of cuttings taken in spring may be placed in the shade and
kept moist but not wet. They should begin to show top growth in
three weeks to two months.
A comfrey experiment
I tried using three rooting mixes (peat/sand,
vermiculite/perlite, and peat/perlite) and two orientations
(horizontal and vertical), with six cuttings of comfrey root in
each category. I placed filled flats under a rhododendron where
they would get some morning sun. I checked them every few days and
watered them only if the medium seemed dry.
At the end of five weeks, top growth was evident on all of the
peat/sand cuttings, all six horizontal and five of the six vertical
vermiculite/perlite cuttings, but only four horizontal and two
vertical peat/perlite cuttings. But top growth told only part of
the story.
When I examined the roots on the cuttings, I discovered five
well-grown root systems on the horizontal peat/ sand cuttings and
one cutting with no roots at all, even though it had a top. All the
vertical peat/sand cuttings had well-developed roots, but two were
growing in the wrong direction (I must have planted them upside
down). The roots, like the tops, of the horizontal
vermiculite/perlite cuttings were all well developed, but only
three of the vertical pieces had both tops and roots; two had tops
and no roots, and the remaining one had a single root and no top.
Only one horizontal peat/perlite cutting had well-developed roots;
the others showed signs of overwatering. The vertical cuttings in
this flat had rotted roots or no roots at all.
I transplanted one of the better-looking plants from each
category into a 41/2-inch square pot filled with a potting mix
containing about equal volumes of peat, perlite, vermiculite, sand,
compost, and soil; watered it; and placed it under the
rhododendron. After a month of warm weather, all of the plants had
developed healthy tops, and each had a nice cube of soil nearly
filled with fine roots. The time from cutting to transplant ready
to go into the garden was just over two months, no matter what the
cutting’s orientation in the flat or which potting mix it had
rooted in.
Lessons on root cuttings
I learned two lessons from this experiment. One was the
likelihood of overwatering. I hadn’t figured on the contribution of
natural rainfall. Even though I watered only when the medium seemed
dry, the peat/perlite mix could be overwatered by rainfall
alone.
The other lesson came as a surprise. Although more cuttings
developed roots and tops in the heavy peat/sand medium than in the
other two mixes, it was very difficult to remove rooted cuttings
from the flat without breaking off many of the small roots. I would
avoid using this formulation again in flats, although it would work
fine when rooting cuttings in individual pots where they could
remain for some time after forming roots. For rooting cuttings in
flats, I would choose the vermiculite/perlite mix. The orientation
of the cuttings makes little difference.
Don’t unintentionally multiply your herbs (or weeds) by tilling
in the root zones of plants that increase readily by root
cuttings—unless you want to create a bed of the stuff. To prevent a
sea of unwanted herbs, carefully dig up the soil with a shovel
between the plant and the area to be tilled and pick out every bit
of root before bringing in the tiller.
Betsy Strauch is assistant editor of The Herb Companion. She and
her husband, Joe, are rooted in Lenox, Massachusetts.