All ponds need regular maintenance to prevent them silting up and turning into bog gardens.

Small ponds need a complete overhaul to remove debris every five years, while large ponds need thorough cleaning every 10 years.

The best time to clean ponds is in late autumn when many creatures are less active. See our separate page for more on maintaining a wildlife pond. Below are some tips on general garden pond care:

Pond cleaning

• Start by preparing a holding tank in a shady spot for fish and deep water plants; use some pond water in the tank, unless it is particularly cloudy. Marginal (water’s edge) plants will survive out of the pond as long as they are kept moist and shaded
• The easiest way to drain the pond is to use a pump, which can be rented for the day from a machinery hire shop
• As the water level falls, remove fish as they become visible
• Remove plants as the water levels drops, placing them in the holding tank. Take the opportunity to re-pot or divide plants if necessary
• If you find any, put larger pond creatures into the holding tanks
• Place decaying plant material on the side of the pond, so any smaller creatures hidden away can return to the pond
• Scoop up the silt from the base. You can use this on your border, but retain a little to add back to the pond as it will help re-establish tiny organisms
• Clean the liner with a scrubbing brush and water, bailing the dirty water out with a bucket
• Return the saved silt and any saved pond water. Next, refill with water (rain water if possible), positioning pond plants as you go
• Finish by returning the fish and any other creatures. After cleaning out the pond, it can take several months or years to return to a balanced ecosystem

Summer pond care

• Water evaporates during windy or hot weather, leading to the water level dropping. The reduced surface area can be damaging for fish as there’s less oxygen available, so top up the pond if necessary. Ideally use rainwater from a butt as tap water is rich in nutrients that causes algae to prosper
• If you do have to use tap water and you keep fish, add the tap water gradually in small amounts to prevent the cold liquid shocking the fish in the pond
• On hot, humid nights, spray water over the surface of the pool from a hose to break the surface and improve oxygen levels in the water. Alternatively, install or turn on a water feature to keep the surface bubbling gently
• Floating weeds can quickly cover the surface of a pond if left unchecked, so twirl these out with a stick or use a net to scoop them out. Leave weeds and algae on the side of the pond overnight, so that larger creatures can return to the water. Rinsing the material in a bucket of pond water can help release smaller creatures which can then be returned to the pond
• Check on any wildlife ramps to make sure they are still in place. These are important in formal ponds where the sides are steep to ensure wildlife can get safely out of the water

Winter pond care

• If the pond is stocked with fish and it does freeze over, melt the ice by placing a hot pan on the surface, or install a pond heater or water feature to prevent freezing occurring. Floating a ball on the water in cold weather can also delay freezing. Never smash the ice, as the shock waves can harm fish
• Improving the oxygen levels in the water by circulating it with a pump benefits both amphibians and fish, particular in deeper ponds where oxygen does not diffuse readily through the water. However, making a hole in the ice is not essential for ponds not stocked with fish
• Ensure plenty of light gets to the pond by pruning back overhanging branches and brushing off snow. This will allow submerged plants and algae to continue to photosynthesize and replenish oxygen levels in the water. Consider adding more oxygenating plants in the spring if there aren't many
• Water levels naturally drop during hot, dry spells in summer but if the drop continues even in winter you may have a leak which will need repairing

Pond plant care through the seasons

• Mid-spring through to early summer is the best time to buy pond plants as the water is warming up and plants will respond by growing away rapidly
• Aim to keep around 50 percent of the surface free of vegetation by thinning out plants occasionally during the summer
• Deep water aquatics with floating leaves, such as water lilies, benefit from regular dividing and re-potting, carried out in spring. Place containers on raised bricks lowered in stages as the plants grow, so the leaves can always reach the surface until the final depth is reached when the plant is mature
• If not being potted on, water lilies benefit from a supplementary feed in the spring with a specialist aquatic plant food to encourage better flowering
• Snip off any tatty leaves, along with any fading flowers in summer. Remove dead leaves and debris from plants early in the autumn to avoid decomposing vegetation building up in the pond
• Thin out excessive growth of underwater oxygenating plants. Four to five bunches (each containing three to four stems) should be sufficient for each square metre or yard of pond surface area​

In late spring, pond algae and weed growth can be rife. There are various ways of controlling and preventing these problems. If you have a large pond with a serious weed or algal problem, then you may choose to contact a contractor or specialist centre for advice.

Links

Centre for Aquatic Plant Management
National Association of Agricultural Contractors (NAAC)