Weymouth, Mass. — You know those packets of unflavored gelatin that with a little imagination can be turned into a hundred sumptuous desserts? Well, they can do wonderful things for your houseplants, too. They can add vigor and new luster to your Boston ferns, African violets, colorful caladiums, or any other of your household favorites.
There's good reason for this, of course: gelatin has been found to be an excellent time-release fertilizer; a natural, nonpolluting, nonburning source of nitrogen.
Most potting mediums have adequate supplies of phosphorus, potassium, and trace elements - all of which are relatively stable in the soil. But nitrogen is another matter altogether. The element that makes plants green and vigorous is highly mobile. It is readily leached out of soil or volatilized into the air. So supplemental supplies of nitrogen, more than any other element, are needed by the houseplant. If that supplemental supply can be provided in a slow-release form so that the plant receives a steady, rather than a feast-or-famine, supply of this nutrient, so much the better.
Gelatin meets these requirements. And because it is an organic fertilizer, its careless use by a horticulturally unskilled homeowner will have far less damaging consequences than most artificial nutrients.
(Table scraps - meat, fish, milk, cheese, nuts, and other protein-rich foods - will break down in soil into nitrogen that can be taken up by a plant. But, to put it mildly, such an approach is ''aesthetically unacceptable'' to a majority of householders.)
Some years ago the folks who make Knox gelatin, knowing that their product (made from skin, bones, and ligament) was pure protein, pondered its possible use as a fertilizer. So they sent quantities of gelatin to Dr. H. W. Scheld, director of development for Simco Inc. at the University of Houston's Department of Biology greenhouses, and asked him to test the theory.
The program was carried out using 49 plant species over a two-year period and the evidence in favor of gelatin's use was conclusive. According to the final report, growth trends were well defined throughout and ''gelatin is, in fact, a very satisfactory source of nitrogen. It is adequate for healthy growth, there is little evidence of a nutritional imbalance, it is difficult to overdose with gelatin, and gelatin fits within the cost range of other sources of nitrogen available to home, amateur, indoor gardeners.''
The trials showed that home gardeners might best apply the gelatin in liquid form at the rate of one packet to a quart of water. It is suggested that one packet of gelatin be dissolved in a cup of hot water and then enough additional water be added to make up a quart. Apply solution once a month.
Chlorific (yellowing, nitrogen-starved) plants were found to improve within 3 to 4 days of being given the liquid gelatin, such is the speed of its conversion to nitrogen.
Gelatin is converted to plant food in this manner: enzymes first break up the protein, after which the bacteria convert it to nitrogen which the plant roots can take up. Plant mixes containing a little unsterilized compost (and therefore a full range of microorganisms) converted the gelatin more readily than those containing largely sterile ingredients. A little rich garden soil added to the mix would also provide an appropriate microorganism mix.