There are several sorts of ingredients or types of aquatic plants to choose from that will be used to plant out different levels or depths in the pool. There needs to be a representative selection of plants from each type to help with the balancing act in the pool, and as each type of plant takes up its role in the new environment they will provide a welcome home for any fish you subsequently add to your pool.
1-The most essential Aquatic Plants Are Oxygenators
These are underwater aquatic 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. They need to be given oxygen 24 hours a day but in return can digest waste organic matter and dead algae converting them into simple compounds like nitrates that the plants in the pool, including the oxygenators, can take up for their own nutrition and growth.
The best and most efficient oxygenator is, without a doubt, Laragasiphon major, otherwise known as Elodea crispa or Curly Pondweed even though this is known as an invasive plant in the USA (North America)
Some folks claim that these aquatic plants are too rampant, but they only grow if there is 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 aquatic plants 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 and nutrients will be absorbed all over the surface of the plant. In hard water, a limey 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 proserpiacoides (Parrots Feather), Elodea Canadensis (Canadian Pond weed),
2-Next in importance are the deep water aquatic plants and water lily varieties
These aquatic plants are mostly water lilies, Nymphaea. Available in virtually every color of the rainbow except blue, the larger varieties act like great “Hoovers” of excess nutrients on the bottom of the pool. They also come in all sizes suitable for growing at specific depths from 6ins to 6ft (15cm to 180cm). Try to get a variety that is suitable to the size and depth of your pool and allow one lily for every 2.3 sq m (25 sqft) of pool surface.
These aquatic plants need to be planted into large aquatic baskets in a heavy clay loam, but only at half their final depth to begin with. Gradually introduce them to deeper water as their leaves get established on the surface. Beware that generally, the cheaper water lilies are, the more vigorous they are. But even the most vigorous types of aquatic plants will need a feed of slow-release fertilizer or bonemeal pellets to get them going. They can be planted at any time from late spring onwards, as long as there is strong growth from a strong plant. Weaker specimens need to be nurtured later in the season.
Keep them away from fountains and waterfalls as disturbed or flowing water upsets their growth.
Other deep-water babies are the amazing Aponogeton distachyos or water hawthorn and the various forms of Nuphar lutea or brandy bottle plant. Owners of small ponds or clay-lined ponds beware of the latter.
These float on the surface of the pool throughout the summer helping control algae by depriving them of light and using up their mineral resources. Native species like the Stratiotes aliodes or water soldier and the Hydrocotyle ranae (Frogbit) over-winter in various forms on the bottom of the pool. Species like the water hyacinth (Eichornia crassipes) and the water lettuce (Pistia stratiotes) are frost tender and need to be over-wintered under glass.
Be wary of any relatives of the duckweed including the floating fern Azolla coronilla. They make great duck food but very quickly and irretrievably cover the pool if there are no ducks to keep things under control.
Whatever you choose, there is no ceremony in planting them. Just put them in. If they sink to the bottom they will soon sort themselves out.
Marginal plants come in all shapes and sizes. They generally sit at the edge of the pool with the water lapping more or less at the soil level. Some plants do revel in a depth up to 15cm as in the case of the Menyanthes trifoliata (bog bean) or Iris pseudacorus (the flag Iris) which makes some people like to classify some of the plants as deep water marginals, but these plants are generally tolerant of any depth and will grow out to the deeper depth anyway.
Marginal plants have the dual function of softening the edges of the pool area and using up the mineral resources in the pool. They provide secure cover for wildlife and act as a jetty for the activities of wildlife in and around the pool. Early spring color, their beauty in reflection and their often striking foliage also help make them an essential ingredient for the water garden.
Allow at least one plant for every 0.5 sq m (5 sqft). Plant them in aquatic baskets and place them in groups of the same variety in larger pools. In smaller pools, I am not sure that having more than one species in one basket works, certainly not in the long run. One of them always seems to win out over all the others.
Beware of what you choose, if there were ever any hooligans in the plant world, then a good number of them would be found amongst the plants often sold as marginal plants. For owners of smaller pools, be particularly cautious in choosing some of the larger and indigenous marginal plants like Typha (Reed Mace), Scirpus (Bulrush), Phragmites australis (Norfolk Reed). They are definitely questionable bedfellows. But you will find that even with these fast-rooting, shooting pond fillers, their misbehavior is moderated by a good cross-section of other more ponderous representatives.
5-Fertilizing Pond Plants
You need to take care here since adding too much nitrate will encourage massive algae growth and even blanketweed invasion. The types of fertilizer available can be granular, liquid (added directly to the water and benefits floating plants most), or in aquatic tablet form. The last mentioned type is added directly to the container at the time of planting.
6-Choose Your Plants To Have A Purpose
Choose the aquatic plants to add color, to add height, to create shade, or to deter algae for example. Use a variety of plants to make an interesting focal point. Remember some plants grow very tall and do this very quickly. Plants create breeding areas for your fish. Eggs stick to the stems and leaves and when the baby fish hatch these plants prove essential cover to prevent all the eggs from being eaten … most will be eaten but generally, a few lucky ones survive to become adult fish.
A rule of thumb for well-established ponds is to provide plant leaf cover for about 50% of the pond surface area. Waterlilies are best for this. The extra shade and cover benefit both the fish and clear water since algae growth is reduced. Algae are also pond or aquatic plants albeit very small water plants.