Planting Aquatic Plants in Containers
In my view aquatic plants are best grown in containers. Not that they do any better, but they are certainly easier to manage. If the pool needs cleaning out they are easy to remove. Likewise, when the plants need lifting and dividing they can be swiftly dealt with. Container cultivation also restricts one variety to its allotted space. A free-for-all amongst aquatic plants leads to an almighty tangle that is very difficult to care for and results in the ultimate demise of weaker and often more desirable plants.
Pots are sometimes recommended for aquatic plant culture, but these are generally unsuitable on two counts. First of all they are of the wrong shape, having too narrow a base, taller plants like irises and rushes continually toppling over. The more important point is that a number of water plants, notably waterlilies, quickly diminish in size if grown in a container that does not have lattice-work sides to allow the free passage of their roots. There would appear to be no scientific explanation for this, and therefore, one can only speculate, but it is a practical fact that many aquatic plants are stunted by normal pot culture.
Proper aquatic planting baskets are now made of plastic and are either round or square with open-work sides and broad bases to ensure stability. Occasionally it is possible to get old-fashioned wooden planting crates and these are equally suitable, if less durable.
If you read a gardening book written at the beginning of the last century, when, as we know it, was in its infancy, it will be noted that all kinds of concoctions are recommended for the culture of water plants. Old rotted cow dung was a particular favourite for waterlilies, together with turf and decayed leaves. Fortunately, we have now discovered that all these old formulas are unnecessary and in many cases can be harmful.
The introduction of rotted manure and turf to a garden pool creates almost instant green water, for the mineral salts liberated as it absorbs the water are legion. If perchance the manure was not in such a state of decomposition as recommended, it could itself pollute the water and kill the. As we will see later, we now do all we can to prevent leaves falling into the pool and creating problems, rather than deliberately introducing them in the compost.
A suitable compost for all aquatic plants consists of gardenfrom which all the debris like sticks, leaves, and pieces of turf has been removed. It should not have been collected from a part of the garden that has been recently dressed with artificial fertiliser, for, like organic matter, this also encourages an algal bloom. Under no circumstances should soil be removed from wet, low-lying areas as this often contains the seeds of pernicious water weeds which may be difficult to remove later.
Having cleaned the soil up and run it through a sieve to remove any large stones, a little fertiliser can be added. This must be of a slow release kind like bonemeal or hoof and horn. It should be used sparingly and in as coarse a grade as possible. The finely powdered form quickly clouds the water and can be toxic to fish.
Before planting, the prepared soil should be dampened to such a consistency that when squeezed in the hand it binds together, yet is not so wet that water oozes between the fingers.
Planting aquatics differs very little from planting ordinary garden plants. Firmness, and positioning at the correct level in the soil being of the utmost importance. Slight variations of technique do apply to certain waterlilies and all submerged oxygenating subjects.
Hardy waterlilies have two different modes of growth. Those derived fromodorata and N. tuberosa producing horizontal rhizomes, while the marliacea, laydekeri, and intermediate varieties usually grow from bulky, log-like rootstocks with fibrous roots arranged like a ruff around each crown. These are planted vertically or at a slight angle with the crown just above the compost.
Before planting a waterlily remove all the old adult foliage. This will eventually decompose anyway and in the meantime will give buoyancy to the plant and may even lift it out of the basket.
Fibrous roots should be trimmed back to the rhizome and any dead or decayed tissue cut back to sound healthy growth. Exposed areas of sound tissue should be dusted with powdered charcoal to reduce the risk of infection and help seal the wound. If a rhizome looks somewhat gelatinous and has an objectionable smell, destroy it immediately. This is almost certainly the highly infectious waterlily.
Marginal subjects are planted in the same manner as one might any other container or pot grown plant. However, submerged oxygenating plants are treated differently. These are usually sold as bunches of unrooted cuttings fastened together near the base with a strip of lead. Although seeming to be clinging precariously to life, once introduced to the pool they rapidly initiate roots and grow away strongly.
They do not rely entirely upon nutrients supplied by the compost and can indeed exist for a considerable length of time just floating about in the water. But rooting gives them stability. The important point to remember when planting the bunches, whether into a container or directly into soil on the pool floor, is to bury the lead weight. If exposed to the water it quickly rots through the stems and the top of the plant falls away.
When all the containers are planted, firm the compost down and add a layer of pea gravel over the surface. This prevents fish from nosing in the soil and stirring it up. At the same time it traps any organic debris in the soil mixture which may float about in the water. The baskets can then be given a thorough soaking with water from a watering can in order to settle the compost and drive out all the air.
Planting the natural way
For gardeners who have a natural water garden, or those who desire to plant directly into the pool, a slightly different technique has to be adopted. Gardeners with an artificial pool are, in my opinion, ill-advised to use direct planting methods for the reasons I outlined earlier in the section on planting in containers. Certainly plants growing in containers are easier to manage and keep within bounds.
The only advice I can offer to those who insist upon direct planting, is to be sure to have a substantial depth of soil, at least 15cm, for the plants to root into. Also cover the entire surface of the soil mixture with pea gravel to prevent the fish from stirring it up.
In a natural pool one has no option but to plant into the floor and banks. Making a hole and pushing the plant into the margin is seldom successful with reeds, rushes and the like. I like to get a plant which has been pot grown and with a decent rootball, for this has stability and grows away much more quickly.
Waterlilies can be placed directly into the pool in a plastic basket or wooden crate. But a more tidy approach is to parcel them up in a square of hessian with a good helping of compost and lower them into position. The hessian eventually rots, but in the meantime the waterlily roots will push through and ramify the soil on the pool floor. Submerged oxygenating plants can be merely tossed in. The lead weight pulling them down into the mulm. Some will come adrift as the lead rots through the stems, but most will take root.