Choosing and planting water plants - Part1: submerged aquatics, plants that oxygenate the water

The most essential ingredient in any pond are the plants that oxygenate the water, often referred to in the aquatics trade as the OXYGENATING PLANTS or submerged aquatics. But what are the best and what ones do you want to avoid. Then how do you plant them?

These are underwater plants that will provide oxygen during the day for the fish and other animals in the pool, but also for the bacteria at the bottom of the pool. These are integral to the whole ecology of the pool and without them the pool would just fill up with dead plant material and fish muck very quickly. These bacteria need to be given oxygen 24 hours a day, in return they digest waste organic matter and dead algae. In a process described as oxidation they convert them into simple compounds like nitrates that all the plants in the pool, including the oxygenators, can take up for their own nutrition and growth. Bascially any plant that grows with it leaves under water is going to release oxygen into the water during the process of photosynthesis. This is the process by which all most plants use carbon dioxide and sunlight to create the building blocks for growth, the sugars and the starches. Some plants are better at this than others. Some are too good at the process for their own benefits and very quickly overtake the pond.

Laragasiphon major syn. Elodea crispa, aka curly pondweed.Hottonia palustris or water violet: Most oxygenators have insignificant flowers that just come up to rest on the surface of the water, but the water violet sends up above the surface a raceme of lilac flowers.
The best and most efficient oxygenator is without doubt Laragasiphon major, otherwise known as Elodea crispa or Curly Pond weed. Some folks claim that it is too rampant, but it only grows if there is the sustenance being created by the pool. It is easily kept under control, with a bit of judicious harvesting.
Most oxygenators are generally sold in bunches of five cuttings. Just push these into a small container of gravel to keep them in place then sink them to a level of roughly half a metre. Allow one bunch per 0.2 sq m (2 sqft) of pool surface. The cuttings will produce roots for anchorage as soon as they begin to grow whilst nutrients will be absorbed all over the surface of the plant. In ‘hard water’ (water with a high pH), a dusty sediment precipitates itself onto the leaves. This should be gently brushed off to allow the leaves to function uninhibited.
Avoid certain plants, in particular Hydrocotyle vulgaris (Marsh Penny Wort), Myriophyllum proserpinacoides (Parrot’s Feather), Elodea Canadensis (Canadian Pond weed). They are permanent problems in ponds and water ways particularly in the south of the country.Myriophyllum proserpinacoides or Parrots Feather: The 'Jekyll and Hyde' of pond plants
Myriophyllum proserpinacoides or parrots feather is often sold as a marginal for its tinted foliage in autumn but it also has submerged foliage that helps oxygenation. Either way it is a pest especially in Cornwall.However recently, demand has revived for it from people wanting to establish 'swim ponds' - the new concept of pond plus swimming pool that has arrived from Austria. For 'swim pond' enthusiasts, one of the main problems that always develops in the water is the build up of phosphates and it has been found that parrots feather is particularly good at absorbing phosphates from the the water. Elodea is a good performer in this respect as well.
Elodea Canadensis has many names like water thyme, water pest, ditchmoss and Babington’s curse. It is the legendary plant introduced in Victorian times that spread the length and breadth of the country at lightening speed along the waterways. I use it to smother surface of marginal plant baskets.

Having told you the worst and best, if you want to see what variety there is availble and that might suit your needs go to the Plant Directory and click on 'oxygenating plants' at the 'Contents' list at the top of the directory. After all, some like Myriophyllum spicatum, water milfoil, loves water with a very high pH and Ceratophyllum demersum or Hornwort is very tolerant of great depth or shade.

Another one to avoid is Stonecrop, Crassula helmsiiThe demon Stonecrop in close up

BUYING OXYGENATORS

For UK residents building ornamental pools, if you want the most efficient oxygenator buy Elodea crispa usually
referred to in books as Largarosiphon major. This can be rampant but it
does the job and canCanadian pondweed, anacharis or Elodea canadensis can be rampant unless kept to the margins easily be kept in check. Dont get palmed off with
Canadian Pondweed (Elodea canadensis, sometimes referred to as Anacharis
or Water Thyme). In a freshly established nutrient rich pond this
really is rampant. But on the plus side, I do find it quit effective
planted almost at water level in the same basket as some vigorous
reeds. Here it can provide an effective green carpet that works as a
useful marginal 'ground cover'.
Whatever you choose, it will be sold in bunches held together with
lead wire. This wire may be heavy enough to sink the bunch if it is
just dropped in. If you did this the weed would probably send out roots
quite quickly and effectively, but ultimately you will find it best to
establish a properly planted group that can be cut and trimmed to size
in relation The dreaded pennywort, Hydrocotyle vulgaristo the point at which it anchored. If you have to hack into
a mass of weed with no beginning and no end you find yourself pulling
most of it out in one long strand and any still in the pool is left
floating on the top.

PROPAGATING AND PLANTING OXYGENATORS

You may not need to buy oxygenators. You may have a friend who has an excellent and well balanced pond that has masses of pond weed in it. All oxygenating weed gets straggly and out of hand. Just cutting the weed back encourages the plants to shoot from bare stems near the point of anchorage or rooting. So taking a few cuttings will be as much a service to your friend as a favour to you.

Collecting cuttings of Elodea crispa all roughly the same length.
The raw material is the fresh growing tips of the plants.These must be kept moist at all times. In bunches of 4 or 5, push them into a basket of inert gravelBreak off tips or lengths of weed 10-20cm (4 to 8 ins) and collect 5 or 6 together in a bunch. Commercial growers tie them together with lead wire.

Push the bunches deep into an inert type of gravel or grit.
Collect tips 4"-8" in length in bunches of 5 or 6 and push these into a planting basket full of pea gravel. It is not absolutelyimmerse the cuttings slowly into the pond. About a foot or 30cm is enough until they get established. necessary to have soil in the basket although some say it helps them get established more quickly, but essentially they just need anchorage.

Place the basket in its position as soon as possible under water at a maximum depth to begin with of no more than 18ins (500mm) but preferably little more than 300mm or 1 foot