How does soil affect herb flavor intensity?

Soil composition influences the strength of herb flavours to the extent that it controls essential oil production in the plant, so that Mediterranean herbs, such as rosemary, develop stronger aromas in gritty, alkaline soils that approach their native habitat. On the other hand, the most delicious leaves and roots are derived from deep, rich blends of composts where plant food is most readily reported and readily absorbed. The best production of terpenes is achieved at the maximum intensity of the combined conditions, resulting in the highest quality.

Stress factors increase the intensity of certain flavours. Light drought stress before harvesting concentrates the oils of rosemary. Limiting nutrients magnifies the pungency of oregano. I find that for the best flavour, I should stop watering some Mediterranean herbs for two days before harvesting; the dry spell induces an oil-producing mode, as it would in nature.

The quality of organic matter in the soil enhances flavor complexity. Compost made from a variety of plants will produce greater herb complexity and better-tasting results. Basil fed to tomato compost has a slightly fruity aroma. Try not to use manure-based fertilizers, as the earthiness can linger in the flavor of the herb. Your next salad bears the stamp of the fields from which the herbs were grown.

Harvest timing strikes the perfect earth-imbued note. Treat Mediterranean herbs, such as rosemary and thyme, to a cut mid-morning, when any dew has dried off the leaves. Snip moisture-loving herbs before they bloom (which makes leaf oils more concentrated) or kelp before it sheds its fronds. Process straightaway or lose the precious volatiles already amassed through your excellent soil feeding.

Read the full article: Best Soil for Herbs: Ultimate Growing Guide