The two troubles perhaps the most common are neither insects nor disease. They are gas and sour soil.
The faintest trace of furnace gas or of illuminating gas will cause trouble, indicated by the yellowing and falling of the leaves and unsatisfactory development of buds. Where there is no way of eliminating the presence of these gases the only way to success with the plants—unless they can be entirely shut off in an enclosed place as suggested in Chapter II—is to take every possible care about leaks, and to give all the fresh air possible.
Sour soil is the result of improper drainage conditions, too much water, or both. It causes the leaves to turn yellow and checks new growth. Making right the harmful conditions will usually renew the health of the plant, but in bad cases it will be far better to remove the earth, wash the soil from the roots, carefully clean the pot—if the same one is to be used—and repot in good porous fresh earth. Keep on the dry side until growth is resumed.
As a rule, insects do much more damage to house plants than is caused by diseases. One characteristic of nearly all plant insects which will astonish the amateur is the marvelous rapidity with which they increase. One to-day, and to-morrow a million, seems no exaggeration. While it may be true that, as one of our erstwhile best-selling heroes said, "a few fleas is a good thing for a dog; they keep him from broodin' on bein' a dog," a few bugs are certainly not good for a plant, because in a day or two there will be enough of them to endanger its life and surely, quickly to ruin its appearance. Never let the bugs get a start. If you take them in time they're easy: if not you have a very difficult and disagreeable task on your hands.
PLANT ENEMIES
Aphis. Aphis or green plant louse is the most commonly encountered of all the insect pests. It used to be dreaded, but with modern methods it may be readily and effectively exterminated. There are several forms and colors of these pests. If you have attempted plant-growing you are undoubtedly familiar with them. In the house, shaded places, crowded plants, poor ventilation, dry plants, all furnish environment favorable to the development of aphids. Change these conditions at once. The old method of fighting used to be by burning moistened tobacco stems, or steeping them in water and making a very weak tea for spraying. But either was a difficult, disagreeable and unsatisfactory method. There are now on the market three forms of tobacco all of which are easy to use and efficient. Tobacco dust—but it must be strong and made especially for the purpose; liquid nicotine, to be diluted and sprayed on according to directions; and prepared paper for fumigating. The last is perhaps the most effective. Besides these, and in my experience pleasanter and quicker, is the comparatively new compound called Aphine, which can be had from almost any seedsman in quart tins—enough to make five gallons of very effective spray, which will not discolor flowers or foliage.
Red Spider. This very serious pest is about the size and color of a grain of red pepper—although sometimes appearing brown or dull red. To make himself inconspicuous, he works on the under side of the leaves and behind a tiny web, but his presence is soon made manifest by the leaves upon which he is at work, which first turn light green, then show minute yellow spots, turn yellow and finally drop off.
The red spider is very tenacious of life, and hard to get rid of when he is allowed time to become well established. The best weapon to use against him, where it can be done, is clear cold water with as much force as possible against the under side of the foliage. Damp atmosphere assists in the work; so keep the air damp, and be on a sharp lookout. Evaporated sulphur, or flowers of sulphur dusted upon the leaves will also help.
Where the collection of plants is not too large a one, the quickest and most certain way to be rid of the spider is to dip the top of each plant quickly two or three times into hot water—140 to 165 degrees. Although uncomfortable to the hand, water of this temperature will not injure the tenderest plant. It is effective against aphis and mealy bug, as well as against the spider.
Mealy Bug. The mealy bug inhabits a white, cottony looking mass, which is easily seen. Remove this covering and the real intruder is there. It is most fond of the soft-wooded plants, such as coleus and fuchsias, thrives in a hot, dry atmosphere, and will keep out of sight, if not watched for, in a mass of leaves or under some branch axis, until there are a large number.