Pond work for May

Last updated 22nd January 2018 from a series written by Alec and Val Scaresbrook for Koi, Ponds and Gardens magazine.

Your pond is starting to really liven up for spring now, and for many, it’s finally time to get the pumps going. Here’s what pond work to do in May.

Plant of the month

Buff up pond plants

About every five to seven years a garden pond is ready for an overhaul. You’ll need to remove the plants, then divide and re-pot any that are bursting out of the their containers. Use sterile loam or aquatic compost. Never use garden soil, because it could contain pesticides or fertiliser.

Clear the majority of sediment from the pond’s base with a pond vacuum. If you want a more thorough clean out, then empty the pond completely, pumping it out with a filter over the inlet to prevent sucking out the aquatic life. Store the last few bucketfuls that harbour all sorts of useful creatures.

If there are fish you’ll need to provide a temporary home for them and net them out before beginning the emptying operation. Fill a suitable container with pond water and cover the temporary home with a net or board to stop the fish jumping out, or being flooded out during heavy rain.

Duckweed control
Duckweed (Lemna minor) is a single-leafed plantlet that floats on the surface and feeds from a fine root beneath its leaf. It dies off in cold winters, with some sinking to the pond’s bottom to reappear in spring, doubling daily in good conditions to rapidly carpet the pond. Although this is useful for blocking out sunlight and using up nutrients, thus reducing blanket weed algae, it is a nuisance for many reasons, depending on your pond’s purpose. You lose the reflective water surface, it shades out submerged oxygenator plants, cats and dogs think it is a solid surface so try to walk on it (possibly damaging the liner when they scrabble out), and birds no longer recognise a possible watering/bathing place

As you can’t stop duckweed appearing, because it is carried from pond to pond on the legs of visiting wildlife, you need a few strategies to control it, unless its presence really doesn’t bother you. If you have fish, they will probably eat most or all of it, but if you don’t have fish, you can only skim out as much duckweed as possible – starting the moment you see it and continuing daily to keep it to a minimum. You could try flushing it out occasionally by flooding the pond but we’ve found that there is always quite a residue that clings to items and plants in or around the pond, and that there’s the danger of soil (and more nutrients) draining back into the pond.

Duckweed thrives in still water, so a fountain, waterfall or other water movement will prevent it proliferating. There are also some duckweed treatments sold (eg from Bradshaws Direct and Pondkeeper) that claim to work selectively without harming any other plant or animal life, but we don’t know anyone who has tried these out so cannot say how effective they are. Since the instructions tell you to remove most of the duckweed first to ensure success, you have to start now, or even earlier, for a fighting chance of skimming out the majority before using the treatment.

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Plant of the month: Hostas

Hostas are unfurling their beautiful leaves now for a foliage display that will last all summer (slugs and snails permitting). They are good for moist conditions in bog gardens, pondside beds and pots in shade or some sun, with the bonus of white or pale blue flower spikes in summer.

The textured leaves are attractive when plain green or blue-green, but many gardeners love the yellow or white variegated forms. There are hundreds of different types to choose from, including ‘Sum and Substance’ or ‘Invincible’ which are less likely to be damaged by pests.

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A timely tip for Koi keepers

When your Koi begin feeding well, mix normal food with winter food before changing completely over to normal food. Always use freshly bought food, never stale leftovers or out-of-date tubs from last year. Bradshaws Direct and Pondkeeper stock food for different seasons and fish.

UV checks
Make the most of your UV unit now and you could have a green-free pond all summer.

Over the next few months you’ll want your UV unit working at its best to combat the seasonal algal build-up. You should routinely replace the bulb at six month intervals to guarantee optimum performance, and check over the connections at the same time. Be sure that the UV tube is covered up if you’re working near it and it’s switched on, otherwise you risk damaging your eyes. You should get into the habit of regularly checking all fittings and joints for good seals especially as you bring equipment back into service for the summer, putting new strains on old connections.

Pump check
If you didn’t get around to servicing your water garden pump before storing it for winter, you need to take a good look at it now. Dismantle it according to the manufacturer’s instructions, clean up the component parts, before reassembling it and checking the pump’s performance.

Covers off
You should remove any winter covers now because they’ve done their job of insulating the pond and the occupants from the chill and will soon have an overheating effect. Poolside plants that are under cover will be forced into unnaturally early growth, and will show their dislike of the great outdoors by turning brown. Try to cover the plants at night for a week or so until they’ve hardened off (i.e. gradually acclimatised to outdoor cool night temperatures).


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