Managing ponds

By Steve Head and Adrian Thomas

Ponds are definitely not no-management garden features, but they can be left to get on by themselves for most of the time.  If you are lucky enough to have a perfectly pure water supply, and can avoid other ways of nutrient build-up, you pond may need little routine maintenance beyond adjusting the spread of vigourous plants to suit your tastes.

For most garden ponds, with a water supply (including tap water) that includes nutrients, the danger is the pond will become increasingly productive or eutrophic.  At best this manifests as extra-vigourous plant growth which quickly covers the pond.  For most wildlife this isn't much of a problem, but amphibia prefer some open water, and so do most gardeners.  At worst, ponds can become cloudy with green "pea soup" water, choked with growth of submerged plants such as Ceratophyllum, and anoxic at the bottom with smelly sulphurous water that will kill many bottom living animals.

Managing submerged plants

Dense accumulations of submerged plants can usually be removed using a lawn rake.  Carefully put it into the water upside down, and use it to scoop out the plant growth.  Make sure you don't damage the liner.

Managing floating and emergent plants

We recommend that plant cover should be between about 50 and 75%, but many water plants grow and spread so fast that they can easily double their area in a season.  They need to be pruned back in the same way as shrubs and trees to maintain the appearance you want.  Be aware however that different invertebrate species favour every stage of pond succession, so by cutting back you will be selecting a particular range of species, often not the rarest.

Floating plants such as Bogbean can be cut back by simply cutting their stems.  Water lilies grow out from a sunken or floating rhizome which can be split as they grow, and old dead lengths removed.  Free-floating water soldier plants can simply be removed if there are too many.

Emergent plants can be easy to remove if (like water mint often is) they are rooted in among other plant roots - just carefully pull them out. Yellow flag iris grows from a rhizome with side roots, and this can be removed in lengths. Other emergents can make substantial masses that can be hard to split and remove.  This is the big problem with densely rooted plants, especially Norfolk reed, which should be avoided in all but the largest ponds.  If you have reeds, you will find they grow out below the water through horizontal stems, which later bind together with knotted roots.  If you regularly (twice a year) prune off the underwater stems, you can significantly hold up the outward growth.

The photos below show the consequences of allowing extensive reed growth in a large garden pond.


Hacking out Phragmites reed from Steve Head's pond.

Top left: Using a tree lopping saw to cut through the dense floating mass of tangled stems and roots in squares. 

Top right: the resultant cube of roots. Pieces larger than this, saturated with water, are too heavy to lift.

Left: The debris pile half way through the massacre.

Removing blanketweed.  Above left: using a rake to slowly pull sheets of weed away from the mass and into reach. Centre: turn the rake upside down and scoop out the weed, drawing and lifting it away. Right: the stranded weed on the bank, with lots of life - common newt and snail eggs visible.  Blanketweed looks horrible but is good habitat!


Dead leaves and debris

It's surprising how fast ponds can begin to fill with coarse debris, and you are advised to avoid putting ponds under trees.  Remember that some leaf debris is good in a pond, providing habitat for caddis larvae, and food for detritivores.  Too much, and the pond bottom (especially if the water is deep and doesn't circulate) can get stagnant, anoxic and smelly.   One solution is to stop the leaves getting into the pond in the first place by netting over the surface and regularly clearing and composting what you catch.

If things have got out of hand and the pond has gone stale in deeper water you might also notice persistent blanket weed overgrowth - there is just too much stored nutrient load in the pond.  The solution can be to net-out the accumulation of debris with a fine pond net.  This is hard work, and disturbs the bottom, filling the pond with suspended debris, and potentially causing a big temporary drop in dissolved oxygen.  If the pond is large, you might be well advised to drain it completely, enabling you to do a proper job. Hire a sludge pump which can cope with small chunks of solids which will foul an ordinary centrifugal pond pump.  Put the sludge on your vegetable patch, where it will be excellent fertiliser.

You should not need to do anything so drastic more than once every few years, unless you have a big leaf and nutrient problem.

Saving pond life during management

We are always advised in pond guides to leave plant material extracted on the side of the pond so beasts can escape and find their way back in.  Certainly newts and large dragonfly larvae seem to be able to do this, but many small creatures including water snails won't be able to.  It's worth remembering that you will have removed much of the habitat these creatures needed to live in, so they may be hard put to survive even if they do find their way back in.  Most of us will leave the material for a while to salve our conscience, but don't let it rot or all the nutrients could wash back into the pond.

If you are forced to pump-out and drain the pond, you will completely disrupt its communities, but many invertebrates will survive among the roots of plants, so will recolonise if you are able to refill the pond quickly after cleaning.  As the pond drains you can rescue beasts you see.  Newts and frogs are best put into moist deep shade, while larvae and snails can be put into shaded bowls - don't let them heat up.

Seasonal management

Spring is the time when ponds come back to life after the winter. The level and duration of sunlight rises, increasing photosynthesis, while the water temperature increases, speeding up metabolism and the pace of life of cold-blooded pond animals.

Over the winter, debris will have blown into the pond and if floating, this can be removed.  There may have been further growth of submerged plants after the autumn clearance, so this can be checked and removed if necessary.

During the winter, slow decay and bacterial action will have raised nutrient levels, and winter winds will help to mix them into the water column.  As water temperature and light levels increase, there may be a temporary burst of algal growth, including blanketweed and duckweed.  This should be removed, and as other pond plants start growing, the nutrient spike should vanish.

Newts and frogs return to your pond to breed in late winter and spring, so this isn't a good time to undertake any heavy maintenance.

Summer:  This is the time to enjoy the beauty of the pond, with growth and flowering of your plants, and the weekly new discoveries of emerging insects and other activity.  Hopefully there shouldn't be much problem with duckweed and blanket weed because submerged and other classes of pond plants are growing so fast.  You may find the submerged plants are growing fast enough to need a little thinning.  It's also worth removing obviously dead vegetation like lily flowers and leaves before they rot and sink.

Autumn:  The pond remains pretty active until the weather gets cold, but amphibian seasonal inhabitants will be leaving the pond to over-winter outside.  Emergent and floating vegetation begins to die back, and can be removed before it falls into the water.  If you do have reedmace however, leave the stems intact, and you will be charmed by goldfinches taking the seeds during the winter. Mid autumn is probably the best time of the year to do any major removal of vegetation or if necessary, cleaning out the bottom.

If your pond is close to a tree, consider netting it over so that the falling leaves are prevented from getting in.

Winter: Hopefully you will have done any major pond clearance while the day is still wrm enough that you don't get chilled.  Other than removing debris falling in and floating, there isn't much that needs to be done, as with the cold weather, the pond essentially shuts down.

If the weather gets really cold, ponds will freeze over which people assume reduces oxygen levels.  This is entirely natural, and isn't a problem for pond wildlife which is a) cold-blooded and torpid and b) are adapted to variable and low oxygen levels.  Surprisingly Jeremy Biggs of the Freshwater Habitats Trust has discovered that oxygen levels in his shallow clean garden pond actually rose during icy spells as the ice prevented loss of oxygen, while photosynthesis below the surface continued.



Resources available from this page:

Managing blanketweed and duckweed
Marginal plants

These are managed much like normal perennial plants, but this can be complicated by the way their roots are matted and embedded in dense muddy soil.  It can be helpful to cut out squares using a sharp spade - but don't damage the liner!  As a general rule, if something is growing fast, don't leave it too long before you intervene.

Blanketweed and duckweed

Both of these are entirely natural, but most gardeners don't like them as blanketweed in particular is very unsightly.  They can appear whenever pond nutrient levels are high, and this can be the case in spring.  Blanket weed can be removed with a garden rake, and duckweed with a pond net.  For more on this see our leaflet Managing blanketweed and duckweed by Ian Thornhill. 
Search
Managing ponds

By Steve Head and Adrian Thomas

Ponds are definitely not no-management garden features, but they can be left to get on by themselves for most of the time.  If you are lucky enough to have a perfectly pure water supply, and can avoid other ways of nutrient build-up, you pond may need little routine maintenance beyond adjusting the spread of vigourous plants to suit your tastes.

For most garden ponds, with a water supply (including tap water) that includes nutrients, the danger is the pond will become increasingly productive or eutrophic.  At best this manifests as extra-vigourous plant growth which quickly covers the pond.  For most wildlife this isn't much of a problem, but amphibia prefer some open water, and so do most gardeners.  At worst, ponds can become cloudy with green "pea soup" water, choked with growth of submerged plants such as Ceratophyllum, and anoxic at the bottom with smelly sulphurous water that will kill many bottom living animals.

Managing submerged plants

Dense accumulations of submerged plants can usually be removed using a lawn rake.  Carefully put it into the water upside down, and use it to scoop out the plant growth.  Make sure you don't damage the liner.

Managing floating and emergent plants

We recommend that plant cover should be between about 50 and 75%, but many water plants grow and spread so fast that they can easily double their area in a season.  They need to be pruned back in the same way as shrubs and trees to maintain the appearance you want.  Be aware however that different invertebrate species favour every stage of pond succession, so by cutting back you will be selecting a particular range of species, often not the rarest.

Floating plants such as Bogbean can be cut back by simply cutting their stems.  Water lilies grow out from a sunken or floating rhizome which can be split as they grow, and old dead lengths removed.  Free-floating water soldier plants can simply be removed if there are too many.

Emergent plants can be easy to remove if (like water mint often is) they are rooted in among other plant roots - just carefully pull them out. Yellow flag iris grows from a rhizome with side roots, and this can be removed in lengths. Other emergents can make substantial masses that can be hard to split and remove.  This is the big problem with densely rooted plants, especially Norfolk reed, which should be avoided in all but the largest ponds.  If you have reeds, you will find they grow out below the water through horizontal stems, which later bind together with knotted roots.  If you regularly (twice a year) prune off the underwater stems, you can significantly hold up the outward growth.

The photos below show the consequences of allowing extensive reed growth in a large garden pond.


Managing ponds

By Steve Head and Adrian Thomas

Ponds are definitely not no-management garden features, but they can be left to get on by themselves for most of the time.  If you are lucky enough to have a perfectly pure water supply, and can avoid other ways of nutrient build-up, you pond may need little routine maintenance beyond adjusting the spread of vigourous plants to suit your tastes.

For most garden ponds, with a water supply (including tap water) that includes nutrients, the danger is the pond will become increasingly productive or eutrophic.  At best this manifests as extra-vigourous plant growth which quickly covers the pond.  For most wildlife this isn't much of a problem, but amphibia prefer some open water, and so do most gardeners.  At worst, ponds can become cloudy with green "pea soup" water, choked with growth of submerged plants such as Ceratophyllum, and anoxic at the bottom with smelly sulphurous water that will kill many bottom living animals.

Managing submerged plants

Dense accumulations of submerged plants can usually be removed using a lawn rake.  Carefully put it into the water upside down, and use it to scoop out the plant growth.  Make sure you don't damage the liner.

Managing floating and emergent plants

We recommend that plant cover should be between about 50 and 75%, but many water plants grow and spread so fast that they can easily double their area in a season.  They need to be pruned back in the same way as shrubs and trees to maintain the appearance you want.  Be aware however that different invertebrate species favour every stage of pond succession, so by cutting back you will be selecting a particular range of species, often not the rarest.

Floating plants such as Bogbean can be cut back by simply cutting their stems.  Water lilies grow out from a sunken or floating rhizome which can be split as they grow, and old dead lengths removed.  Free-floating water soldier plants can simply be removed if there are too many.

Emergent plants can be easy to remove if (like water mint often is) they are rooted in among other plant roots - just carefully pull them out. Yellow flag iris grows from a rhizome with side roots, and this can be removed in lengths. Other emergents can make substantial masses that can be hard to split and remove.  This is the big problem with densely rooted plants, especially Norfolk reed, which should be avoided in all but the largest ponds.  If you have reeds, you will find they grow out below the water through horizontal stems, which later bind together with knotted roots.  If you regularly (twice a year) prune off the underwater stems, you can significantly hold up the outward growth.

The photos below show the consequences of allowing extensive reed growth in a large garden pond.


Marginal plants

These are managed much like normal perennial plants, but this can be complicated by the way their roots are matted and embedded in dense muddy soil.  It can be helpful to cut out squares using a sharp spade - but don't damage the liner!  As a general rule, if something is growing fast, don't leave it too long before you intervene.

Blanketweed and duckweed

Both of these are entirely natural, but most gardeners don't like them as blanketweed in particular is very unsightly.  They can appear whenever pond nutrient levels are high, and this can be the case in spring.  Blanket weed can be removed with a garden rake, and duckweed with a pond net.  For more on this see our leaflet Managing blanketweed and duckweed by Ian Thornhill. 
Dead leaves and debris

It's surprising how fast ponds can begin to fill with coarse debris, and you are advised to avoid putting ponds under trees.  Remember that some leaf debris is good in a pond, providing habitat for caddis larvae, and food for detritivores.  Too much, and the pond bottom (especially if the water is deep and doesn't circulate) can get stagnant, anoxic and smelly.   One solution is to stop the leaves getting into the pond in the first place by netting over the surface and regularly clearing and composting what you catch.

If things have got out of hand and the pond has gone stale in deeper water you might also notice persistent blanket weed overgrowth - there is just too much stored nutrient load in the pond.  The solution can be to net-out the accumulation of debris with a fine pond net.  This is hard work, and disturbs the bottom, filling the pond with suspended debris, and potentially causing a big temporary drop in dissolved oxygen.  If the pond is large, you might be well advised to drain it completely, enabling you to do a proper job. Hire a sludge pump which can cope with small chunks of solids which will foul an ordinary centrifugal pond pump.  Put the sludge on your vegetable patch, where it will be excellent fertiliser.

You should not need to do anything so drastic more than once every few years, unless you have a big leaf and nutrient problem.

Saving pond life during management

We are always advised in pond guides to leave plant material extracted on the side of the pond so beasts can escape and find their way back in.  Certainly newts and large dragonfly larvae seem to be able to do this, but many small creatures including water snails won't be able to.  It's worth remembering that you will have removed much of the habitat these creatures needed to live in, so they may be hard put to survive even if they do find their way back in.  Most of us will leave the material for a while to salve our conscience, but don't let it rot or all the nutrients could wash back into the pond.

If you are forced to pump-out and drain the pond, you will completely disrupt its communities, but many invertebrates will survive among the roots of plants, so will recolonise if you are able to refill the pond quickly after cleaning.  As the pond drains you can rescue beasts you see.  Newts and frogs are best put into moist deep shade, while larvae and snails can be put into shaded bowls - don't let them heat up.

Seasonal management

Spring is the time when ponds come back to life after the winter. The level and duration of sunlight rises, increasing photosynthesis, while the water temperature increases, speeding up metabolism and the pace of life of cold-blooded pond animals.

Over the winter, debris will have blown into the pond and if floating, this can be removed.  There may have been further growth of submerged plants after the autumn clearance, so this can be checked and removed if necessary.

During the winter, slow decay and bacterial action will have raised nutrient levels, and winter winds will help to mix them into the water column.  As water temperature and light levels increase, there may be a temporary burst of algal growth, including blanketweed and duckweed.  This should be removed, and as other pond plants start growing, the nutrient spike should vanish.

Newts and frogs return to your pond to breed in late winter and spring, so this isn't a good time to undertake any heavy maintenance.

Summer:  This is the time to enjoy the beauty of the pond, with growth and flowering of your plants, and the weekly new discoveries of emerging insects and other activity.  Hopefully there shouldn't be much problem with duckweed and blanket weed because submerged and other classes of pond plants are growing so fast.  You may find the submerged plants are growing fast enough to need a little thinning.  It's also worth removing obviously dead vegetation like lily flowers and leaves before they rot and sink.

Autumn:  The pond remains pretty active until the weather gets cold, but amphibian seasonal inhabitants will be leaving the pond to over-winter outside.  Emergent and floating vegetation begins to die back, and can be removed before it falls into the water.  If you do have reedmace however, leave the stems intact, and you will be charmed by goldfinches taking the seeds during the winter. Mid autumn is probably the best time of the year to do any major removal of vegetation or if necessary, cleaning out the bottom.

If your pond is close to a tree, consider netting it over so that the falling leaves are prevented from getting in.

Winter: Hopefully you will have done any major pond clearance while the day is still wrm enough that you don't get chilled.  Other than removing debris falling in and floating, there isn't much that needs to be done, as with the cold weather, the pond essentially shuts down.

If the weather gets really cold, ponds will freeze over which people assume reduces oxygen levels.  This is entirely natural, and isn't a problem for pond wildlife which is a) cold-blooded and torpid and b) are adapted to variable and low oxygen levels.  Surprisingly Jeremy Biggs of the Freshwater Habitats Trust has discovered that oxygen levels in his shallow clean garden pond actually rose during icy spells as the ice prevented loss of oxygen, while photosynthesis below the surface continued.



Resources available from this page:

Managing blanketweed and duckweed
Hacking out Phragmites reed from Steve Head's pond.

Top left: Using a tree lopping saw to cut through the dense floating mass of tangled stems and roots in squares.  Top right: the resultant cube of roots. Pieces larger than this, saturated with water, are too heavy to lift. Below: The debris pile half way through the massacre.

Removing blanketweed.  Above left: using a rake to slowly pull sheets of weed away from the mass and into reach.Above right: turn the rake upside down and scoop out the weed, drawing and lifting it away. Below: the stranded weed on the bank, with lots of life - common newt and snail eggs visible.  Blanketweed looks horrible but is good habitat!