As spring progresses, water
lilies and marginals send shoots to the water’s surface to begin their seasonal
cycle anew. Have you looked below the water’s surface? While you may have been
busy this spring potting decorative plants in patio containers, you might not
have thought to lift your aquatic plants to see what’s going on inside their
Like other perennial plants,
aquatic plants increase in size each year. Many aquatic plants grow from
rhizomes or tubers that would spread out to form a larger clump each year if
they were growing in their native habitat. Since they are confined to pots,
they can become crowded and stunted if not maintained.
There are a few
techniques that differ from dividing and potting up terrestrial plants. First,
the planting containers need to accommodate roots that grow horizontally rather
than vertically, so shallow but wide containers are the best. Water garden
experts recommend using either plastic pots without drainage holes or mesh bags
designed specifically for growing aquatic plants.
Second, you need
to use clay
loam or special aquatic plant potting soil. Regular bagged potting soil usually
contains peat, ground bark, perlite and possibly pumice—all of which will float
to the top of your pond as soon as you submerge your aquatic plant. Since I
have an abundance of clay soil in my garden, I collect a few shovels-full in
the area where I’m working. I sift through the soil to remove plant roots and
In most cases, you will fill
a container one-half to three-quarters full of clay loam, and will arrange the
plant’s rhizome, bulb or roots in the pot before topping it off with more clay
loam. Aquatic plants and marginals prefer to have their crowns at the same
level, or just above, the soil’s surface.
Once you’ve positioned
plant in its new container and filled it with soil, top off the pot with an
inch of pea gravel. The gravel will support the plant’s crown and keep soil
from washing into your pond.
Before the season progresses any further, roll up your
sleeves and divide your aquatic plants! Here are some suggestions for repotting
different types of aquatic plants.
Water Lilies (Nymphaea)
Water lilies have vigorous rhizomes (fleshy roots) that
can cause their pots to bulge after just one season. The second season after
you bring home a water lily you may notice that it has two crowns sprouting
leaves instead of the original one. (I poke a couple of fertilizer pellets down
into the soil of my second-season plants.) If your water lilies have been in
their original pots for more than two seasons, they will produce fewer and
smaller leaves and flowers. It’s time to repot!
Remove your water
its pot and use a hose to wash the soil away from its roots. If you simply want
to repot your water lily, select the strongest-looking crown, and cut away
excess rhizome, roots and damaged foliage, leaving four or five inches of
healthy rhizome attached—and discard the rest. If you want to propagate
additional plants, leave sections of root attached to all the crowns that look
healthy and pot each up separately. Use an old kitchen knife, a root saw, or
pruners to cut the rhizome. Fill
your container three-quarters full of soil. Place the plant’s crown against the
side of the pot and spread the roots toward the center of the pot. Then,
backfill around the roots with more soil to just below the plant’s crown. Add
your one-inch layer of pea gravel, fill the container with water, and place it
in the pond.
Plants With Rhizomes
Use the same technique to
wash soil away from the rhizome of plants like iris or cattail. Cut the rhizome
into good-sized, four-inch sections, making sure each section has an “eye” or
crown. Remove any soft, mushy portions and discard.
Fill a wide container with soil, leaving four
inches or so
between the top of the soil and the top of the pot. Lay the rhizome
horizontally on top of the soil, with the crown near the edge of the pot.
(Positioning the root at the edge of the pot allows the plant’s roots to grow
across the surface of the soil.) Just cover the rhizome with soil and add an
inch of gravel. It’s ready to return to the pond. This technique works for any
marginal plant with a large horizontal rhizome.
There are a number of plants that
grow happily in flower
beds as well as in the pond. These plants are divided in just the same way as
they would be for terrestrial planting. The only difference is that the soil
should be clay loam, and it needs to be topped off with pea gravel. Leave the
crown of the plant just level with or slightly above the surface of the soil
and the gravel will support it.
Unlike water lilies, marginal plants need to have the tops
of their containers just a few inches below the water’s surface. They are ideal
for placement on the shelves or shallow areas near your pond’s edge. They won’t be happy where the top of the
pot is a foot or more below the water’s surface.
Aside from the differences in containers
repotting aquatic plants isn’t any more difficult than other garden plants.
Your plants will thank you!