Water is one of the most vital ingredients in our gardens.  

Few of us are lucky enough to have natural water or man-made pond large enough so that they do not need intervention (400 square metres and 1.5 metres deep in parts).  Anything smaller and there will be a need to tinker with it to keep it sweet.

Blanket weed's quite a nuisance, probably caused by too much nitrate or phosphate which trigger blanket weed to grow at a phenomenal rate.


Rainwater is also a big culprit, as it tends to be full of nutrients, and we have had several deluges over recent months.

Hay nets of barley straw which works in about 60% of cases, but it's difficult to source these days.  Why is does not always work is a bit of a puzzle to the freshwater biologists.  It does take a good month or two, though, and you must remove it before it starts to disintegrate, otherwise it increases the nitrogen levels and causes even more algae.

One idea is to add barley straw extract instead (from agagroup.co.uk), which is quicker and easier to manage, but if it doesn't work then it's suggeted that we try Aqua Activ Algo Universal (oase-livingwater.com) from Oase, which has a helpline for pool-related queries (01264 333225).  This control does not alst as long as the more natural method.

The fail-safe but expensive, method is to use a sonic machine that zaps the weed continually but it costs around £800 for an area of water around 150 square metres.

Another common pest problem is invasive vegetation (reeds etc) which can cover the entire pool.  To combat this, either use glyphosate carefully to spray the vegetation (it is not harmful to fish if used correctly) or you can cover the base before they emerge (or cut down first) with a needle punch root barrier (£2.35 per square metre from Aga group, as before).  You will need to weigh it down initially with rocks or silt.

The best way to avoid the pea soup situation is plants, plants and more plants.  Ash Girdler, a pond expert for the Aga group, recommends covering two thirds of the surface area with floating leaved plants such as water lilies, water soldier (Stratiotes aloides) and frogbit (hydrocharis).  Another three-quarters of the sides, at least, should be planted with emergent and marginal plants such as irises, flowering rush (Butomus umbellatus) and water forget-me-not (Myosotis scorpioides).

It'a a good idea to add some  bunches of submergents such as spiked water milboil (Myriophyllum spicatum), not to be confused with the highly invasive parrot's feather (M. aquaticum).  Fish, especially carp, will gobble these up, though, so you may need to cage the plants.

Lilies are best contained in baskets so that some water can be seen.  These vigorous lilies start pushing their leaves way up out of the water when they become congested and every few years the need to be hauled out, split and replanted in the garden.

Some gardeners think their pool base should look like the bottom of a clean bath.  This would be quite horrible for wildlife.  What they really want in the base is about 150mm or more of good, healthy hydrasoil (mud!), which if it has been left untouched, will be there anyway.  

If not sure, take out a scoop and smell it.  If it stinks of rotten eggs or methane, then maybe there is some anaerobic or partial decomposition.  In this case add some Aquabio (calcium sulphate, from Agagroup).  This should either be applied in early June or late summer; it will slowly sweeten the pond.


Planting marginal plants directly into the soil, which covers the whole pool/pond base, gives a better balance.  Small quantities of basketed plants can look rather wimpy.  Topsoil is too rich and makes everything turn green and clay subsoil and fish are a bad combination, as the clay fines cloud the water when the fish move. A poor, sandy subsoil is best.

A good way to hide the liner is to add pre-0vegetated coir rolls.  These are sausage-shaped 3m-long rolls, 200mm in diameter.  They bend and can be fixed either just below water level, or partially above it and they will sprout wonderful, lush, emergent plants (ornamental and native mixes, from the Aga group).

If starting a new pool or pond, the choice of liner is very important.  Butyl has been superseded; EPDM rubber is far better. It's not degraded by UV light and has a 25 year guarantee.  Make sure it's 1mm thick and put a blanket underlay (NP300) below and usually above the liner too.  If labradors, children and deer are going to stray in, it protects the liner.



From an article by Bunny Guiness (The Telegraph Life Gardening pages, 9 June 2013)