A plant's life cycle begins with germination, recognized by the above-ground appearance of a growing shoot. Mated to this shoot are two small, round leaves known as cotyledons (A). Once these leaves begin manufacturing food, the plant begins to grow and enters the seedling stage. During this time the plant develops it first set of true leaves, resembling those of a mature plant. The primary formation of a root system begins. The root development that takes place at this time is key to the rate at which the plant will continue to grow. Providing the proper environment for the roots will ensure that your crop will have a chance to flourish.
Once the root system can support further growth, the vegetative stage begins. Nutritional requirements at this time call for large amounts of nitrogen, required for the production of chlorophyll, as growth during this period is primarily stem, branch and leaf. The most substantial growth over the lifecycle of the plant occurs in the vegetative stage and will continue unless interrupted by a change in environment or lack of water/nutrients.
The final stage of the organisms lifecycle is the reproductive stage. Because the objective is now to reproduce, and thus carry on evolution, energies are directed to the manufacture of flowers, seeds, and fruit. The primary nutritional requirements begin to shift at this time from a high-N diet to a low N, high P-K diet. This is due to a considerable slow down in vegetative growth while reproduction takes place. This change prompts a switch in nutrient solutions from a vegetative formula to a flowering, or 'bloom' formula. Many hydro-ponic nutrients now come as a two part system for exactly this reason. In some plants, reproduction is triggered by a change in the length of daylight, this characteristic is called photoperiodism. It is this characteristic which governs when these plants may be sown and harvested if growing outdoors. Indoors, be sure to provide the proper photoperiod for your crop or they may never fully develop. Changing the length of artificial daylight can trick the plant into flowering early. Commercial growers use this trick to deliver flowers to markets out of season and at a premium to vendors and customers alike.
If you are growing indoors, for lack of natural insects, you must play "bee" by pollinating the flowers on your plants manually. For tomatoes and peppers a delicate touch with a brush on each flower will help the plant pollinate itself to produce fruit. There are commercially available plant "shakers" that vibrate the flowering plants every so often to accomplish the same. I have found that the breeze from a strong circulating fan is usually sufficient to cause pollination indoors.
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