Pond work for July

Last updated March 2018
Updated from a series written by Alec and Val Scaresbrook for Koi, Ponds and Gardens magazine.

Hot days, balmy nights, perfect gardens. We can only hope that this year’s summer will turn out to be truly summery.

Of course, perfect gardens do require some work, and warm weather means evaporation, so ponds and water features will need frequent topping ups, with good quality water in the case of Koi ponds. Warm weather also means active fish and filters, so oxygen demands will be high, especially during still nights.

The long light evenings provide plenty of time to get on with essential tasks, so here’s a list of what to do in July before you relax to contemplate the results of all your hard work.

Plants – add more
Plant of the month – water lily
Blanket weed control
Duck weed control
Project – self-contained water feature
Fish – ensure aeration
Fishkeepers – holiday arrangements

Add more plants

With ideal conditions of warm air and water, aquatic plants grow strongly now, so those planted this month will establish quickly and help your fight against algae.

Use sterile loam or aquatic compost to pot up plants into special containers with mesh sides (see Bradshaws Direct). Never use garden soil because it could be contaminated by algae-encouraging fertiliser, and poisons such as slug killer. To prevent fish disturbing the plants and the compost, add a layer of pebbles to the pot.

Submerged aquatics are the easiest to plant. Sold as bunched cuttings, you simply push these into pots before placing at the recommended depth. Even easier is Hornwort (Ceratophyllum demersum); you just throw it into the pond to grow just below the surface.

Floating plants do a very good job of cutting out light, but beware of those that spread so well that they hide the water’s surface altogether. Fairy moss (Azolla) is one of these. And some, such as water lettuce (Pistia stratiotes) and water hyacinth (Eichhornia crassipes), won’t survive frosts, so you’ll have to overwinter them indoors or buy ankew each year.

Marginals (eg from Pondkeeper and Thompson and Morgan)are the other big group of aquatics, preferring some water above their pots, but not too much. It’s important to get the depth right otherwise the plants won’t thrive, but most labels and catalogues give detailed information about each plant’s requirements.

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Plant of the month: Water lily

Water lilies are the stunners of the water garden, providing a glorious display of colour floating on beds of broad leaves during long summer days.

White, yellow, red and orange shades are available, but be sure to look at vigour as well as flower colour. The most vigorous lilies are suitable for lakes, not garden ponds. At the other extreme, the least vigorous are better suited to water barrels than ponds.

The key to choice is water depth, so be sure to check recommendations before buying. Specialists give details in their catalogues, so you can be sure of obtaining exactly the right plant for your pond.

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Blanket weed control

Warm water, high light levels and excess nutrients all contribute to blanket weed problems. This nuisance is an algae that produces thread-like growths, which wrap around plants and block equipment. Excessive growth is unsightly, with clumps floating at the surface, although these are easier to rake out than the strands clinging to pipes and so on. It occurs in all types of pond, with or without fish.

In our pond, which has no fish, we’ve seen frog tadpoles eat the blanket weed, and in recent years since our frog population crashed, we’ve seen fewer tadpoles and more blanket weed, so they were probably keeping it down at a critical time of year.

Blanket weed can be minimised with good pondkeeping practice. So fish keepers, especially Koi keepers, should make sure that fish are quickly eating all the food provided (if food is uneaten, it adds to the nutrient levels in the water). The filters should also be working as efficiently as possible to deal with the high levels of fish waste at this time of year. And make sure that nutrients in the form of garden fertilisers aren’t washing into the water.

If possible, shade the water with submerged and floating plants (mentioned in the previous section), or grow large-leaved prostrate plants at the water’s edge to overhang and shade some of the pond. Shade netting stretched over a pergola at the sunniest times of year is another good way to reduce light levels.

There are also a variety of devices and treatments available (from Bradshaws and Pondkeeper), but do check if they are compatible with fish and other water life. One device that water gardeners either scoff at or report success with is in-line magnets, with the more expensive type (requiring mains electricity to induce the magnetic effect) appearing to be far more useful. Possibly these magnetic devices are better at flocculating algal spores than the long strands of weed, so need to be in place before there’s much of a problem? This might be the reason for different success rates. As the cheaper version of permanent magnets fitted in line are reported by some as good at controlling lime scale, these might be worth a try anyway if you need to deal with this problem.

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Duckweed control

You need to keep on with controlling duckweed – see pond work for May for more information.

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Project – self-contained water feature

A small water feature on or by the patio is a great addition to the garden, even if you’ve already got a water garden or Koi pond. Small ponds in sunken pots, half-barrels or pre-formed liners add interest to a patio corner or to a planted border. Alternatively, a self-contained feature with water bubbling up provides a safe sound of water for those with children to consider.

The most important aspect to consider, if you intend to use a pump, is disguising the electricity supply cable. As you’ll have to remove the pump in winter to protect it from freezing, you should also think about the appearance of the feature without water flowing.

There are plenty of kits supplied complete with pump for you to set up your own self-contained feature quite quickly. To install a pebble fountain, you simply dig a hole to take the reservoir and pump, or, for a raised feature, build a sturdy surround to support and hide the reservoir. For a wall feature, be sure to use strong enough fixings to support the weight of the bowl plus water. And think about how to disguise the return water pipe, such as clipped behind trellis uprights.

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Fish keepers in general and Koi keepers in particular should keep an eye on aeration at all times, but never more so than during warm weather. At this time, when the pond water is warm, the fish are at their most active, since they are cold-blooded and react to the temperature around them. Then they feed well too, and in turn generate higher levels of waste that beneficial bacteria in the filters can convert to less harmful substances. However, bacteria can only convert the waste if there’s enough oxygen for them, and Koi need higher levels of oxygen too in this active phase. Unfortunately, the warmer water becomes, the less oxygen it can hold, so you need to do all you can to maximise aeration, so take a look at our articles and consider airstones, venturi, aerated bottom drains, splash returns, and waterfalls and fountains.

Do check the pond water’s oxygen levels regularly, and take some measurements at night too because plants (including blanket weed and other algae) add oxygen during the day, but use it at night. If the levels are worryingly low (around 6mg/l or less), install more aeration devices as soon as you can. And it’s sensible to keep waterfall and fountain pumps running at night, especially if you have a pea soup of a pond.

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Holiday time for fish keepers

If you’re planning a summer holiday and have found someone to care for your fish, it’s a good idea to show them round your setup earlier rather than later. Make sure that they know exactly what you want to do (draw up a list in advance so there’s time for queries) and for Koi keepers, be sure to give them a specialist’s contact details for emergency advice.

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