May is brimming with warm weather, sun and the promise of summer. It is also the time when nasty blankets of green filamentous algae appear on ponds. The mere sight of these algae drives into desperation owners of water features, and especially of the smaller kind.
The green algae are not all bad – they absorb quantities of water-soluble nitrates and phosphates before other aquatic plants spring into action. But they look slimy, they cling to water plant stems, they get in the way of fish, and so they need to be removed. Best way to do this is by using a garden fork or a rake – when hair-like colonies of algae get stuck between the thongs of the rake, twist it around a few times and pull the algae onto the pond edge. Be careful not to get into the water, seeing as the algae are quite heavy.
Leave them for a few hours on the edge of the pond so that all tiny creatures, such as beetles or small frogs, have time to disentangle themselves and return back into the water. Often algae contain small fish fry, so pick out the larger fish and put them back in the water. After a few hours, move algae to the compost heap, since this is an excellent fertiliser. But bear in mind – when out of the water and drying, the algae become a source of very unpleasant odor.
As soon as spring arrives and the weather warms up, green algae start appearing on all natural and artificial water features, which do not have water filters installed. This is only natural, and there is no need to despair. However, you do have a problem if algae keep growing all throughout the season. This indicates that natural balance of your pond is destroyed. Green algae also develop fast in brand new water features, which have not been stocked yet.
Warmth, sun, pH of water, water-soluble nutrients and shortage of oxygen – these are the main causes that encourage growth of algae. To prevent green algae and to keep their growth in check, plant a lot of aquatic plants, which are natural competitors of algae for absorbing nitrates. The common reed (Phragmites australis), broadleaf (Typha latifolia) and narrow leaf bulrushes (Typha angustifolia), sweet flag (Acorus calamus), reed manna grass (Glyceria maxima), species of pond weeds (Potamogeton) and Canadian waterweed (Elodea canadensis) are choice plants for the purpose. They are much better looking than the green filamentous algae, and they also help to keep water clear. Another group of important plants are the water lilies (Nymphaea). Their lush foliage provides ponds with shade, which inhibits growth of algae. It is also known that a warm and sunny spring is conducive to growth of algae. Besides, the water lilies assimilate great quantities of nutrients.
The moving and oxygen-enriched water discourages the growth of algae, so presence of underwater springs, fountains and fish helps. But be careful when introducing fish – too many of them, and their excrements will only increase quantities of nitrates in the water. So the biological balance of the water feature is all-important. The problem might also go away, provided the gardener has a little patience to wait for a few months, refraining from using any chemicals.
A number of other plants are useful oxygenators – water weeds, spike rushes (Eleocharis), water soldiers (Stratiotes) and floating frog bits (Hydrocharis). The growth of algae is discouraged by soft water, so small water features are best filled with the rainwater.
The water always becomes clearer after the rain, which cools, softens the water and enriches it with oxygen. Special biological additives are also useful (Penac, Septic Gobbler) – they disintegrate organic substances and help to form active sedimentary mud. However, unless you eliminate the underlying causes, the algae will reappear sooner or later. Therefore biological water filters are recommended for small artificial water features where natural balance is difficult to maintain. [banner]
Preventative measures against algae in an established pond:
* remove all fallen leaves and dead vegetation from the pond in autumn;
* do not fertilise soil around the pond;
* control numbers of fish and aquatic plants in the pond;
* remove any blankets of green algae from the water as soon as they appear.
Preventative measures against algae in a new pond:
* the prime task is to stock the pond with aquatic plants. Marginal aquatics absorb nitrates; deep-water plants assimilate nitrates and oxygenate water; and water lilies provide with surface cover.
* introduce fish only after the plants become well established. Do not overdo with the number of fish – both the common and Crucian carps need little encouragement to multiply fast.
* do not use ordinary herbicides to fight algae, they will only worsen the situation, besides, they are detrimental to aquatic fauna.
* keep small water features topped up with rain water during the hot days of summer.
* if you do not have time or willingness to fight algae, use water filters. They are important even if the pond is only to be used for keeping fish rather than plants.
Repotting marginal aquatics
There is no need to divide aquatics which are planted in the soil at the bottom of the pond, unless you need to prevent them from spreading too aggressively. Aquatic plant, grown in open-sided plastic baskets, should be lifted and repotted every year or every 2 to 3 years, depending on the size of the basket. Draw the basket with the plant out of the water and wait until the water drains. Remove an entire plant and divide into several pieces so that every portion has some healthy roots (or a piece of rhizome) and several growth buds. Fill the basket with heavy loam, and top it with a layer of gravel to prevent soil disturbance. The planting basket with wide-meshed sides should be lined with a piece of hessian or similar material.
Having planted the baskets, lower them slightly into the water and wait until the air bubbles stop surfacing. Move the baskets into their final planting position.
© Giedra Bartas, 2013