If you are repeatedly growing in the same spot outdoors, the leaves of your plants are yellowing or you are growing basil indoors, then you may want to fertilize. You should fertilize only once or twice per growing season for outdoor plants. It is recommended, for edible herb and vegetable gardens, to use a balanced fertilizer where the nitrogen content does not exceed 20 percent. A typical fertilizer that would be recommended for edible gardens is one rated 10-10-10 (the percentage of nitrogen, phosphorus and potassium in the mix, respectively). Stronger fertilizers should only be used when plants are being watered thoroughly and the drainage is good, to help prevent fertilizer burn.
For indoor plants, a lower potency of fertilizer is recommended and it can be applied more frequently, perhaps every 3-4 weeks. Always apply fertilizer around the base of the plant and never on the leaves or stems.
A practice many gardeners prefer to using artificial fertilizer is to use composts on soil prior to planting. Compost provides nutrition to your garden but does so more slowly than artificial fertilizers. This is because compost must become biologically available or “break down”, a process which can take months or years. Another highly regarded food for your herb garden is liquid kelp spray. Kelp not only provides nutrients, but it has been found to control garden pests as well as help prepare some perennial herbs for cold winter weather. Indoor herbs sprayed with liquid kelp have been found to be more tolerant to low-light conditions as well as dry soil.
Your basil plant should be pruned several times throughout the season. This will encourage new growth and is especially important if using the herb for culinary purposes. This can be done after the plants have grown at least 6-8 inches. When harvesting basil, I prefer to cut a stem just above a pair of leaves. Leaflets next to the topmost leaves are then converted into new stems. After several months of growth your plant will begin to flower and form seed. At this point the basil will grow more slowly if the flowers are not pruned away, and it will begin to turn bitter to the taste. Simply remove the entire flowering part from the stem by cutting or pinching.
Migrating for the Winter
Well, basil plants don’t migrate on their own, but if you want to prolong their life you can transplant them into containers and move them into a warm, sunny location indoors. You must do this before first frost. Basil will do best near a south-facing window (if you reside in the northern hemisphere) or it can be grown under certain types of grow lights, as described in How to Grow Basil Indoors. The good news is that you can enjoy basil all year round!