What is the best soil mix for raised herb gardens?

These beds are constructed with layered soil. The bottom layer consists of coarse, well-draining rocks, while the nutrient-dense layers above nourish the herbs. Water cannot pool to drown the plants, and beds warm quickly in the spring to maximize the growing season. Volunteers and weeds cannot penetrate them as easily. Be careful to adapt these layers for your specific herbs.

Start with a gravel foundation for drainage. Lay 2 to 3 inches of coarse gravel at the base of the bed. This layer aids drainage and prevents soil from compacting and rotting roots. Increase to 4 inches for a deeper bed. This drainage should allow Mediterranean herbs to thrive, even in rainy weather.

Middle Layer A combination of topsoil and compost, with equal parts of high-quality topsoil and mature compost, is best. "Adds nutrients, supports structure. Sand for Mediterranean section. Sprinkle in coconut coir where moisture-loving herbs grow to achieve a perfect home for roots".

Keep your raised beds well-maintained. Top dress every spring with a layer of compost; check that the drainage layers are free from leaf matter at least every two years; and replace the herb-specific top couple of layers when necessary. A little work on your part will enable your beds to last longer and your herbs to perform better; with good care, they will provide plentiful harvests for five years or more.

Match your bed height to the herbs you want to grow. Mediterranean herbs require at least a 12-inch depth, but moisture-loving plants will fare better in 18-inch deep beds. The taller the bed, the warmer it gets, but also the quicker it dries out. Choose your size depending on your climate. I have varied the height of my beds to suit the needs of each herb, and it has resulted in some bumper harvests.

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