Last updated March 2018Updated from a series written by Alec and Val Scaresbrook for Koi, Ponds and Gardens magazine.
August is a quiet time for pond work, but as we move through the month, it is worth thinking, alas, about the end of summer, so you can plan essential chores and planting.
Plants – planning for colour around the pond
Plant of the month – chameleon plant (Houttoynia cordata variegata)
Plant pests – look for vine weevil
Pond – planning how to deal with autumn leaves etc
Fishkeepers – monitor fishponds for health and water problems
Plan ahead for planting
Thinking ahead, what will your pond’s surround look like once your summer plants finish flowering, or die back altogether? The area could end up looking rather bleak. For a more interesting look during autumn, choose some temporary or permanent evergreen plants for their attractive leaves. Also, choose some plants with colourful flowers, fruit or stems to cheer the scene.
These autumnal brighteners can be planted in pondside beds or containers. The plants in containers will need more care because plant roots are naturally below ground where they are insulated from the cold winter air. To make the roots less vulnerable choose large containers that take plenty of insulating compost. Consider lining the inside of the container with bubble plastic or polystyrene chips, or alternatively use naturally insulating tubs made of wood or polystyrene.
Temporary plants include autumn and winter bedding such as pansies, polyanthus, ornamental daisies and ornamental brassicas. For a range of seasonal bedding plants (sold as plugs) and seeds, look at Jersey Plants Direct, Suttons Seeds, or Thompson & Morgan
Permanent plants that are possible include autumn/winter flowering heathers (check whether they need an acid soil), , and shrubs with attractive stems such as dogwoods (Cornus spp), corkscrew or dragon’s claw willow (Salix matsudana or S. babylonica var. pekinensis‘Tortuosa’), dwarf conifers and snakebark maples (Acer spp).
Looking ahead to January onwards, plan which early-flowering bulbs you should order and plant in autumn for a colourful display next year. See our guide to bulbs for more information.
Some water plants (such as water chestnut (Trapa natans) and water hyacinth (Eichhornia crassipes)) are tender and are killed outright by cold weather, so if you don’t want to buy more next year move these soon to a frost-free place. Some bog garden plants may not survive winter either without some protection, such as a thick mulch. Fortunately, Gunnera manicata, which looks like a giant rhubarb, provides its own mulch as its large leaves are very useful for folding over the crown (i.e. main growing point) and protecting it over winter. However, not all of us have large enough gardens to accommodate this impressive plant. If so, there is a smaller cousin, Gunnera magellanica for good ground cover, and it’s hardy.
Some aquatic plants die down to buds that then sink to the bottom of the pond, until things warm up again in spring. There’s no need to do anything with these because they can survive our winters if the pond is deep enough. However, they will take a while to get going again in the spring.
If you want some pond plants to grow as early as possible to combat the inevitable algae in spring, take some fairy moss and frogbit indoors and bring them into the warmth early on. You can then return them to your pond as soon as the air and water temperatures rise again.
Plant of the month:Houttuynia cordata variegata
This is a popular water garden plant, known as the chameleon plant, with colourful leaves and creeping habit, although once it takes hold it can creep too far for comfort. It will grow in damp borders as well as in water, and is happy with up to 2in of water above its crown, so it is a good plant to grow at the edge of a pond to disguise the liner.
The plant has heart-shaped leaves of gold, green and red, growing on red stems. Planted for its attractive foliage, it also puts on a show of small white flowers in August and September. You can probably buy it locally from your garden centre, but if not, try mail order from Thompson & Morgan.
This prominent gardeners’ enemy has taken a liking to many plants, not just vines. The first you may know of it is when your favourite plant keels over. The adult weevil (always female) eats the edges of leaves, producing a scalloped effect, but far more damage is done after the adult lays its eggs close to a plant stem.
The larvae that hatch burrow their way down to the roots and feed on them for about three months, causing the plant to wilt and then die. Each adult can lay 500 to 1,200 eggs over a few months, usually in spring, but sometimes they are as late as November, and even over the winter in greenhouses.
Fortunately, control is possible. Switching to loam-based composts such as John Innes types and avoiding peat is the simplest. Kill any adults you find (look at night with a torch) and use a biological method to control the larval stages, treating the soil/compost with nematodes that are the larvae’s natural enemies.
There are also two pesticides available to gardeners to treat compost in containers but we would prefer not to use them since they are neonicotinids, even though they are not the types that have been banned while the effect on bees is investigated. Thiacloprid (available as Bayer’s Provado Vine Weevil Killer 2) is toxic to aquatic life, should never be used in the ground, only in containers, and should never be used for edible plants. Acetamiprid (available as Scott’s Bug Clear Ultra Vine Weevil Killer) is not considered particularly toxic to aquatic life but again is only for use for non-edible plants in containers. The problem with soil drenches is that any that runs out of the bottom of the container could enter your pond, your garden soil or be taken up by food plants. We think bees are so precious to human life that using any neonicotinid is risky until thorough testing has proved they are safe for pollinators.
Dealing with debris and autumn leaves
All you need to keep out debris this autumn is a fine-mesh net. Secure pegs in firm ground around the pond and stretch a nylon fishing line across the pond beneath the net to stop it sagging in the middle. Nets do a wonderful job of keeping out leaves and other debris, so consider buying one if you haven’t already (Bradshaws Direct and Pondkeeper have a range). If you already have one in the shed, find it now and check it over for damage. Make sure that you know where the securing pegs are too. If you haven’t enough, tent pegs are also useful for keeping the net in position. Once the leaves begin falling and pond plants start to die back, usually after the first frosts, cut your pond plants back to the top of their baskets to make it easier to spread the net over them.
Powered surface skimmers are a less obtrusive way of dealing with debris, with Bradshaws Direct and Pondkeeper having a selection. Some skimmers connect to a pond pump; others have an integral pump. For example, Oase’s pond surface skimmer, which looks like a chimney, is simple to weight down in a pond with the inlet able to adjust automatically by 12cm to follow fluctuating water levels. Lotus have a similar product but this is set manually to the height required. Floating versions are also made by Oase and others.
See our full guide to surface skimmers too.
Fish – monitor for health and water problems
Keep an eagle eye out for parasites and other health problems, and remember that your Koi may be gasping because of gill problems, not lack of oxygen in the water. A quick water check with an oxygen test kit will help you decide where the problem lies – test kits are available from Koi specialists such as East Riding Koi Co.