High quality soil is the key to any healthy herb garden. First, you must determine what type of soil you have, and then you can establish a plan for improving and/or maintaining it. This is one of the most important aspects of gardening because, along with needing water and sun, plants need nutrients that they get from the soil to grow healthy and strong.
One of the first things to do with regard to your soil is to determine the pH. Then, you will be able to determine which plants will do well in your garden. Some plants prefer alkaline soil and some prefer acidic soil. They will not do well if grown in soil that they do not like and they may even die. You can measure your soil's pH by using a simple test kit. The pH of neutral soil is 7. Acidic soil has a pH below 7. Alkaline soil has a pH above 7. The optimal range for your soil is between 6.5 to 7 which will be acceptable to most plants.
If you are growing your herbs in a bed or in rows, you will need to dig up the soil and add compost or other organic materials. This will insure that your plants develop the best possible root structure. Adding organic matter is the single most important thing you can do for your garden. It improves and maintains soil health. If you have really heavy clay soil, do not dig the soil. Doing so will expose the heavy subsoil which is almost impossible to cultivate. Instead, spread a good layer of compost on top of the soil and plant into that.
If your herbs are not perennials, that is, not lasting more than one season, you could plant a cover crop during the off-season. Common cover crops are grasses and legumes such as: winter rye, oats, buckwheat, clovers and alfalfa. Cover crops are good for the soil quality. They leave behind many of the important nutrients that your herbs need.
Here are some types of soil you may encounter in your home garden:
Sandy Soil - Sandy soil is light and free draining. It often dries out quickly in hot summers. It can be improved by digging in layers of organic matter such as compost.
Peaty Soil - This type of soil retains moisture well and is easy to work with.
Loam - This is the best garden soil, especially if it contains 8-25% clay and the rest is silt and sand. It retains water, has good drainage, and is highly fertile.
Clay Soil - Clay soil is dense, difficult to work, and needs drainage. It is fertile, however, and the texture can be improved quite easily.
You may be growing your herbs in planter boxes or containers. This is a great option if you have limited space such as a patio or balcony. This is a great choice for those of you who do not have the right garden soil for the herbs you want to grow. Planting in your own container gives more control over the soil quality.
You can purchase good soil mixes at garden centers and nurseries. Look for "planter's mix" or "perennial soil mix."