This section is from the book "The Gardener's Monthly And Horticulturist V26", by Thomas Meehan. See also: Four-Season Harvest: Organic Vegetables from Your Home Garden All Year Long.
The conditions which I recommend for successfully growing tropical aquatics (i. e., still, warm water, and a rich compost) favor the growth of a low form of vegetable life called confervae, or green scum, which becomes very unsightly and troublesome unless eradicated. As the result of several years' experience, I am quite positive, that if abundance of goldfish are kept in the tank or pond, there will be no trouble in this direction. Other kinds of fish which are vegetarian in habit might perhaps answer as well, but the German carp is not to be recommended for tanks kept solely for the choicer varieties of aquatics, on account of their propensity for rooting in the mud, and feeding upon the fibrous roots which proceed from the rhizomes of the lilies. Should it be determined to keep a few German carp in the "lily garden" it will be necessary to place whole pieces of roofing-slate, or large pebbles, on the soil around the crowns of the tender Nymphaes.
Innumerable kinds of aquatic insects breed in the water, and some of their larvae prey upon the leaves of the lilies, but the common watersnail is the greatest enemy of aquatic plants. The goldfish assist very materially in destroying these larvae and snails, but I have found a complete preventive of injury to the foliage from this source, by keeping in the tank, in addition to the goldfish, some of the common spotted sunfish. They are carnivorous in habit, and very alert and active. Moreover, it is impossible for mosquitoes to breed in a water lily basin in which abundance of the above-named fish, or those of a similar habit, are kept - or, more strictly speaking, their larvae can never leave the water alive.
Thus, one objection to locating these tanks or ponds in the vicinity of the dwelling-house is removed. Their beautiful appearance and the ease with which they may be taught to feed from the hand (though it must not be done too frequently), make them a charming adjunct to the water garden. If the tank is two feet or more in depth, they can be left in it all winter with perfect safety in this latitude. Sometimes, towards autumn, brown aphides or plant-lice become troublesome on the lily leaves. A somewhat new insecticide which any one can prepare has proved effectual with me. It is called the kerosene emulsion, or kerosene butter, and is prepared as follows: Take two parts of kerosene and one part of thick sour milk. Warm the latter (to blood heat only), put the two liquids together, and agitate violently with a greenhouse syringe or a force pump. They will soon completely unite, and form a white soapy mass. This kerosene butter mixes readily with tepid water. One part of the butter should be thoroughly mixed with fifteen parts of water, and applied to the infested leaves with a syringe.
With me, one application entirely destroyed the insects without any injury whatever to Nymphaes. A weaker solution of the emulsion must be used on any plants which are found to be injured by the proportions above given. Experience will be a guide in this matter. Very few applications of the remedy will be needed during the season. I am indebted to the Rev. Dr. J. H. Brakeley, of Bordentown, N. J., for the suggestion as to the use of the kerosene emulsion for this purpose. He had previously experimented with it upon the cranberry worm, and had met with gratifying success.
Those who attended the meetings of the American Pomological Society, last September, will remember that Prof. Riley also gave this insecticide great prominence. Why can it not also be used in the greenhouse and the flower garden? Is any one experimenting? If so, let us hear the result. In its native waters Nelumbium luteum is sometimes infested with a worm which penetrates the leaf at its junction with the stem, and eats downward into the heart of the stem. It also feeds upon the leaves, partially rolling up a portion of the edge and spinning a web under which to work. If their progress is unchecked, they will do much mischief to the foliage, and as yet there seems to be no remedy but killing them by hand. Great care should be taken that this insect (for no doubt the parent of the worm is a moth) is not brought to our gardens. "Forewarned is forearmed." I therefore caution any who attempt to transplant N..luteum from its habitat during summer time with foliage attached to the plants. They should be carefully examined and every worm destroyed. As the tubers are formed under water, if these are removed while dormant, of course no insects will be carried with them. I would here remark that few who try to dig tubers of N. luteum out of a muddy pond will ever attempt it a second time.
It is a little too much like going after Chinese yams under water. Nelumbium speciosum is never attacked by this worm, unless infested plants of N. luteum are placed near it. Bordentown, N. J.