by Kit Knotts - Click images to enlarge
Pea soup may be fine in the kitchen but not in your pond!
Having clear water is sometimes the greatest challenge that faces
the water gardener. In most cases the answer is a simple one
- leave the pond alone.
We believe that clear water is best achieved by allowing the
pond to achieve natural balance. This means finding the proper
combination of plants, fish, snails, beneficial bacteria and,
believe it or not, algae. Expensive and/or complicated filtration
Green water is the worst way a pond can be murky. This occurs
when nutrients in the water exceed the plants available to utilize
them, allowing single celled algae to thrive and turn the water
green. This often happens in spring as the water warms. In a
healthy pond, plant growth will soon catch up and the single
celled algae will go away on their own.
In our view, the quickest way to establish the health of a
new pond (or one recovering from winter) is to add dirt, debris
from other ponds (even from the compost pile), fish, snails,
and any plants available. We will even "transplant"
mossy or rooted algae.
One of the first water gardening books we read contained the
sentence, "Algae is your friend" or something like
that. There are thousands of types of algae, some awful to look
at, some annoying and some rather attractive. The mossy type
that adheres to the sides of a healthy pond is very beneficial,
as are the rooted types. The point is that you can choose what
you want to inhabit your pond.
Dirt, sludge and silt (the combination sometimes called "mulm")
on the bottom of the pond provide a home for beneficial bacteria
necessary for overall pond balance. We never clean our ponds
but, if it should be necessary, we would consider jump-starting
the bacteria population with one of a number of multiple-bacteria
products on the market for ponds.
As a rule of thumb, 40% of the water's surface should be covered
with foliage of some kind in cooler months, increasing to 70%
in the warm months. The foliage shades the water, keeping it
cooler (discouraging algae) and the plants utilize some of the
nutrients in the water (discouraging algae).
Encouraging plant growth discourages algae growth. Most aquatic
plants require at least five hours of full sun to grow well,
more sun whenever possible. Because algae is more adaptable,
it can out-compete plants in a pond that is too shady. Plant
selection for shade tolerance is a factor in this case if pruning
to provide more sun is not possible.
Fertilizing plants will NOT promote algae growth, as many
seem to think, if applied properly. Aquatic fertilizer tablets
are designed to break down quickly once wet. It's important to
place them well into the soil and cover the hole after doing
so. This will prevent rapid escape of the nutrients into the
water. The benefits of fertilizing regularly far outweigh the
risks of creating more algae.
Probably the second least desirable algae to the single-celled
type are string algae. Other than increasing plant coverage,
there is no remedy for them except manual removal. They will
go away when plant coverage is adequate for pond balance without
them utilizing the excess nutrients.
Water hyacinths (if they are legal where you live) utilize
nutrients and absorb heavy metals far better than any other pond
plant. If used, they should be anchored to the side of the pond
with string or wire. Even though they are floaters, they don't
like to float around. Overgrowth is easily remedied by thinning
but disposal must never be in an open waterway as they are
Waterfalls and fountains are pleasant additions to many ponds
but a pump placed on the pond bottom can keep sediment stirred
up, making the water murky. Elevating the pump off the bottom
will solve the problem in most cases.
Small native fish are the best choice for pond balance, are
usually self-limiting in numbers and they reduce or eliminate
mosquito development. Fancy fish can keep the sediment stirred
up. They also contribute their waste to the nutrients available
for algae growth. Limiting the fish population and feeding them
little if any supplemental food (beyond what is available naturally
in the pond) will help keep the nutrients at a manageable level.
Snails are the pond clean-up crew, eating decaying matter.
Ramshorns are the best bet. Large decorative snails from the
pet shop should be avoided as they do eat healthy foliage.
Soil selection for planting can also be a factor in water
clarity. Top soil can turn the water black and clay can make
it milky. Both will settle out in time but the discoloration
will return any time the pond is disturbed. Placing a layer of
plain sand or gravel over the soil will reduce its escape into