Spring should be upon us in April/at Easter, with the whole garden waking up, including waterlife. So it’s time to prepare your plants, pumps and take a stand against predators…
A timely tip for Koi keepers
Even though it’s getting warmer it’s still important to keep monitoring water temperatures, and to start feeding when they reach 10°C. Remember to check that the fish are interested in the food and if not, stop feeding and try again in a week or so.
Pondwork for April/Easter: beat the bloom
Pond and pondside plant info for April/Easter: plant and divide
Pond(side) plant of the month: April
Fishkeepers: Pondwork for April – equipment check
Fishkeepers: Pondwork for April – deter predators
Ponds: beat the algal bloom
If your pond is going to turn green at all, it’s likely to be around now because of the increased light levels that enable algae to make use of nutrients in the water. Later in the year, water plant growth makes use of surplus nutrients and shades out light; without this competition, any algae in the water can multiply rapidly.
To provide competition and reduce algal blooms, use starwort (Callitriche autumnalis), which is a British native plant that remains active throughout winter. This plant is usually sold as a weighted bunch of cuttings to just drop into the pond, or they can be potted up and submerged with around 18in water over them. They soon establish, with the star-shaped leaves growing as a floating mat on the pond’s surface, providing some shade and a habitat for insects, amphibians and fish. If the foliage begins to take up too much of the pond, it’s easy enough to pull some out.
Alternatively you could grow some floating and submerged aquatic plants (from Pondkeeper or Thompson and Morgan) indoors over the winter, ready to introduce to the pond once frosts have finished. These plants will prove to be more active than those left overwintering in the outdoors pond, and will give a head start on beating the unsightly green algae.
Although aquatic plants are available mail order online, it’s easy to phone round your local aquatics/water gardening suppliers (see Yellow Pages or online yellow pages) to see what you can pick up.
Plant and divide
Start planning which perennial plants to split up, either for tidiness or for filling in gaps around the garden, and pot up any spares you’ve got to swap with other gardeners. It’s best to split up congested water lilies, marginals and bog plants once they begin growing again at this time of year, but leave irises until after they have flowered otherwise you’ll miss out on their display.
If you have a plant clump which is growing in the ground, dig it up completely to divide it. If the plant is in an aquatic planter, you may have to destroy the container to extract the plant. Shake off as much compost or soil as possible before cutting off or prising away the outer portions of the clump, and discard the older central section and re-plant the divisions into individual planters or spaced out in the ground. Use fresh aquatic compost for planters and top off with gravel or pebbles.
Jargon buster: The crown is the lowest visible part of the plant, where the stems emerge from the soil.
Plant of the month
Marsh marigold (Caltha palustris) is a favourite plant in the water or bog garden at this time of year. It suddenly bursts into colour with its shiny solidly yellow 5cm wide flowers giving a promise of sunshine, and it keeps on flowering from as early as March to as late as July.
It should be planted in the bog garden or in a pot on the edge of the pond so that its roots are always moist, but the crown should not be submerged. Look out for double-flowered variants such as Plena or Monstrosa and the compact white-flowered version Alba.
Also look out for marsh marigold in packs of marginals, such as from Pondkeeper.
Fish-keepers – equipment check
With the weather becoming milder your pond heater shouldn’t be necessary now, so it’s best to remove it. You will need to dry it out thoroughly and store it out of the way until the chilly weather returns. But before you store it, look for any visible signs of deterioration, especially around the cable and connections, and repair or replace them if needed. Your heater should be stored away from temperature fluctuations in order to prevent heat and ultraviolet light prematurely degrading any materials.
If you switched off the air pump for winter, the time has come to check it over. When the weather warms up and the fish activity increases, more oxygen is needed to ensure effective breakdown of waste in the filters with enough air left over for the fish. Most Koi keepers favour an airstone or two in the filter system, and one or more in the pond. Additionally, an air dome over the bottom drain can benefit the water quality of your pond because it introduces air to the water, which is similar to the job performed by the venturi inlet to the pipework.
By carrying out these routine equipment checks you can relax this summer in the knowledge that all will be in full working order when you want to use them again.
Fish-keepers – scare predators
You can prevent herons from wading into your pond by using trip wires or low fences. A net on a frame over your ponds surface is also a good barrier, and, if fitted to the top of a pergola over the pond, will camouflage Koi without impeding your view or the growth of surrounding plants. For those more serious Koi keeper there are also various birdscarers which can be installed, based on predator eyes or loud bangs triggered by motion sensors (which could be annoying at night!). Just don’t fall for the plastic heron (unless as an ornament) since we’ve seen herons fishing close to each other – they are just not territorial enough to be deterred by another’s presence. In fact it could indicate to them that there’s good fishing to be had.
Cats are more difficult to deter, although they often look rather than strike. Making the surrounds high enough above the water to put the fish out of reach is one answer, but there are also motion sensor ultrasonic devices that deter cats from lingering too long. An automatically resetting deterrent using a water jet is extremely effective at repelling cats too, and perhaps herons, but remember to turn it off before going into the garden otherwise you’ll get a soaking. We speak from experience.