Shelf gardening with fluorescent lights may be the trend of the future, since the materials are so inexpensive, and easy to obtain. Fluorescent lamps are great for shelf gardening. In this system, many shelves can be placed, one above the other, and fluorescent lamps are used on each shelf. Some shelves have 24 hour lighting, some have 12 hour lighting (for flowering). Two areas are best, perhaps with one other devoted to cloning and germination of seed.
Shelf gardening assumes your going to keep all plants 3′ or shorter at maturity, so all shelves are 3-4 feet apart. Less light is necessary when you have plants that are this short and forced to mature early. One drawback to a shelf garden like this is that it is very time consuming to adjust the lamp height every day, and it is harder to take a vacation for even a week with no tending of the garden. This applies mostly to the vegetative stage, when plants are growing as much as an inch per day. Lamps on the flowering shelves are not adjusted nearly as often. Normally, the lamps should be kept within 2 inches of the tops of the plants, with the plants arranged such that they get progressively taller as the end of the lamps go up, so that all plants are within this 2″ range. This is an ideal however, and if you do go on vacation, adjust the lamps so that your sure the plants will not be able to grow up to the lamps within that length of time.
If enough fluorescent lights are used to completely saturate the shelf with light, the spacing issue will not create spindly plants. They will merely grow a little slower if the lamps are not very close to them. An alternative is to use fluorescent lamps for cloning, germination and early seedling growth on the top shelf of a closet, then switch over to HPS for heavy vegetative growth and/or flowering in the main closet area. Position the HPS such that it won’t need adjustment, at the top most possible point in the closet or room. Most HPS installations will not require lamp height adjustment. Just attach the lamp to the underside of shelf or ceiling as high as possible, and if you want to get a few plants closer to it, put them on a temporary shelf, box or table to get them closer to the lamp.
A shelf is all that is necessary with this type of setup, preferably at least 18″ wide, up to about 24″ maximum. This area must be painted a very bright white, or covered with aluminum foil, dull side out to reflect light back to the plants. (Dull side out prevents hot-spots; diffuses light better.) Paint the shelf white too. Or, use aluminized mylar, a space blanket, or any silvery surface material. Do not use mirrors, as the glass soaks up light.
Hang shop lamps from chains and make sure you can adjust them with hooks or some other type of mechanism so they can be kept as close to the plants as possible at all times (1-2″). If the lamps are too far from the plants, the plants could grow long, spindly stems trying to reach the lamp, and will not produce as much bud at maturity. This is due to internode length being much longer. This is the length of stem between each set of leaves. If it is shorter, there can be more internodes, thus more branches, thus a plant that provides more buds in less space at harvest time.
Shelf gardening is sometimes referred to as Sea of Green, because many plants are grown close together, creating a green canopy of tops that are grown and matured quickly, and the next crop is started and growing concurrently in a separate area of continuous light. Clones are raised in a constant light shelf, until they start to grow well vegetatively, then placed on a 12 hour per day shelf to flower.