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Pond maintenance is essential to ensure that your pond is in the best possible shape to survive the winter and be ready to thrive when spring comes around. It is also important to ensure that your pond doesn’t become overwhelmed by algae blooms and blanketweed in the spring.
If your pond is well established, it may to a certain extent maintain its own healthy ecosystem, particularly if you have a good balance of pond plants to keep the water oxygenated. However, newer ponds may need a little extra maintenance to keep everything on an even keel. Here are some jobs to do this autumn.
Rotting leaves can give off toxic chemicals as they decay, so use a net to remove any leaves that have fallen into the water. If there are deciduous trees near to your pond, trim them back to minimise leaf fall. Some people choose to put a net over the pond to prevent leaves from entering, but this can interfere with the wildlife, particularly if you have a lot of frogs, so try and ensure that are still some exit and entry points.
Remove excess vegetation
Some species of submerged aquatic plant can grow prolifically during the summer, and they should be thinned out to avoid them overtaking and choking out other plants. Use a rake to lift out vegetation, and leave it by the side of the pond for at least a couple of hours before putting it in your garden waste bin to allow any aquatic creatures to crawl safely back into the water.
The pond should have around one third of the surface clear of floating vegetation to allow enough sunlight to reach the water, so clear enough overgrown plants and blanketweed to allow for this. Duckweed is a real nuisance in ponds as it quickly spreads to cover the entire surface. Apart from looking untidy it will cut out all light getting into the water which harms submerged aquatic plants and can deoxygenate the water.
Whilst it dies back in the autumn it hasn’t gone away, as its spores sink to the bottom of the pond and will re-emerge in the spring. Remove as much as you can before it disappears and stock up on some eco-friendly duckweed control product so that you can start to treat it as soon as it reappears next year.
Trim back marginal plants
Remove any leaves and flowers that are beginning to wilt from plants to avoid them decaying in the water. Upright marginal and emergent plants should be cut back to about 15 cm growth above the water level (unless the care instructions say otherwise: there are some species of grasses and ferns that shouldn’t be trimmed). The foliage of some reeds and rushes looks attractive even when it has died, so as long as it is not rotting down it can be left if you wish to provide winter interest and cut back in early spring before new growth emerges.
Remove any dying growth and dead plants, but be careful not to get rid of perennial plants that may go brown in autumn and winter and renew themselves in spring. Plants that are completely dead will have mushy roots that have rotted and will smell a little unpleasant, whereas plants that are dormant as part of their natural growth cycle will still have healthy roots.
If you are not sure, carefully pull the plant up and take a look at the roots. Get rid of anything that has died, and consider if you need to replace it. Maybe your pond did not have ideal conditions, such as part shade or part sun, for the plant to thrive, so consider this when choosing a new plant.
Reduce excessive growth of submerged oxygenating plants
Submerged pond plants such as Willow moss and Hornwort are essential to help oxygenate the water and create a healthy environment for wildlife. They absorb excess nutrients such as nitrogen and phosphorus to help reduce the growth of algae.
In the springtime, these plants also play an essential role in providing shade, food, and shelter for wildlife. Amphibians and insects will use the leaves to lay their eggs on. Ideally, there should be a bunch of floating plant for every 1-2 sq metre of pond, and they should take up about 25-30% of the volume of the pond.
If any growth has been getting out of hand, pull or rake out any excess, leaving it by the side of the pond to allow any pond creatures to escape back into the pond. While you are maintaining the vegetation, keep an eye out for any banned invasive species, which are listed on the Gov.UK website.
Signs your pond might need extra care
A wildlife pond is best not completely cleaned out, because you may disturb dragonfly and other insect larvae, and disturb amphibians that may be overwintering in the pond. However, sometimes a pond can become polluted by too much decaying matter and a lack of oxygen. You may notice a noxious smell and a build-up of sludge on the bottom of the pond.
In this case, you will need to use a fine net to remove the layer of silt and sludge from the bottom of the pond. Do not remove all of it as it contains essential nutrients for the other organisms in the pond and huge amounts of beneficial bacteria which help to maintain a healthy pond
A very neglected pond may need completely clearing out, and autumn is an ideal time to do this when breeding wildlife should have left. However, be vigilant for any creatures that you may find during the clean out. Shake plants to dislodge any hiding creatures, and leave the plants for a day or two to allow any remaining creatures to escape.
Any creatures you do find should be placed in a bucket of pond water rather than tap water, to avoid exposing them to harmful chemicals.
When emptying water from the pond, store as much of it as you can rather than drain it away, because it will be rich in nutrients. When the pond is empty, check the liner for any splits and damaged areas, and apply patches if necessary. Do not be tempted to scrub the liner clean as this will be hard work and you will damage the natural biofilm (aka slime!) that has accumulated over the years: this contains billions of pond-friendly bacteria that are an important part of the ecosystem and help keep the water healthy.
When refilling the pond, use as much of the conserved water as possible, and top it up with rain water collected in a butt, or allow it to be refilled naturally when it rains. This is far preferable to using tap water that contains chlorine and other chemicals, because it will inhibit the growth of plants and may damage the wildlife.
Decide which plants you want to return to the pond, ensuring that you have a good mix of submerged, floating, and marginal plants. Where possible, choose native species that are hardy enough to survive the winter and will be non-invasive and wildlife friendly.
Hardier species can be planted in autumn, but avoid bare rooted water lilies and irises, because these will do better when planted in the spring.