Basil originates from warm climates and grows very well whenever the temperatures stay above the frost level. Basil does, however, begin to bolt pretty quickly once the temperatures begin to get hot.
Bolting Defined:
Bolting is when a plant produces a flowering stem (or stems) before the crop is harvested, in a natural attempt to produce seeds. Once seeds have developed on a basil plant the flavor of the leaves diminishes greatly .
Here is how to prevent Basil from going to seed:
Keep the plant in shade.
During the hottest parts of summer, the sun in Zone 9 can be quite intense. The intense sun will cause Basil plants to bolt rather quickly. Keeping the plants in shade will help keep the temperatures down and will reduce the intensity of the sun. Thankfully basil grows VERY well in containers and when planted in one, it can be moved to a shady, cooler part of the garden rather easily. When planted directly in the ground, the plants can not be moved, so the best option is to use shade cloth.
Shade cloth is a fabric that will allow sunlight trough the fabric (at a reduced level) that allows the plants to continue to grow, but will greatly reduce the intensity allowing for temperatures to be reduced. Some shade cloth manufactures claim the cloth can drop temperatures from 15-20 degrees. We most frequently use this brand of shade cloth.
Keep the plant well watered.
While basil does not like to have soggy roots, frequently watering the plant during the heat of summer can help reduce the stress of the heat and sun. Make sure not to over water, allowing the soil to drain properly before watering again. Another thing to be aware of is if you are watering the plant during intense sun periods to be careful not to get the leaves wet as the water droplets will often amplify the sun and burn the leaves.
Harvest Often
Harvesting leaves often, sometimes as often as daily. will help reduce the plants attempts to bolt to seed. Frequent harvest will also help keep the plant concentrating on growth instead of reproduction helping increase the yield of the plant over the growing season. During the hottest times of the year, picking leaves even if not needed is a good practice to help keep the plant from bolting.
Trim Frequently
During the warmer months of the year basil will grow rapidly and should be trimmed by 1/3 at least once a month. The plant should also be trimmed at the first sign of a flowering stem being produced. This frequent trimming will keep the plant focused on growing more leaves and stems and less focused on producing seeds. Basil flowers form a large bud compared to plant size, which makes it very easy to tell when flowers are about to develop. At first sign of flower development cut the stem about 1” directly below the developing flower.
