I have put in hay nets of barley straw in the past (barley straw is difficult
to source now) but it does work in about 60 per cent of cases. Why it 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.
This time I am adding barley straw extract instead (from Agagroup),
which is quicker and easier to manage, but if it does not work I will try Aqua
Activ Algo Universal from Oase, which has a helpline for
pool-related queries (01264 333225). This control does not last as long as
the more natural straw 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
150sq m.
Another common pest problem is invasive vegetation (reeds etc) which can cover
the whole pool. To combat this, either you can 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 sq m 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). You
should add some bunches of submergents such as spiked water milfoil (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.
I originally planted lilies directly into the soil on the base of my pool some
30 odd years ago, using a rampageous white water lily. Now I have contained
them in baskets so we can see some water. These vigorous lilies start
pushing their leaves way up out of the water when they become congested and
every few years we lug them out, split and replant them in the spring.
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
you have left it untouched, you probably have anyway. If you are not sure,
take a scoop out and smell it. If it stinks of rotten eggs or methane, then
maybe you have some anaerobic or partial decomposition. In which case add
some Aquabio (calcium sulphate, from Agagroup). You have just time now to
add it, or wait until late summer; it will slowly sweeten it.
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.
If you want to add marginal plants now, maybe to hide your liner, a great way
to do it is to add pre-vegetated coir rolls. These are sausage-shaped
2m-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 you are starting a new pool or pond, the choice of liner is very important.
Butyl has been superseded; EPDM rubber is far better. It is not degraded by
UV light and has a 25-year guarantee. Make sure it is 1mm thick. I always
specify a blanket underlay (NP 300) below and usually above the liner too.
If labradors, children and deer are going to stray in, it protects the
liner.
