How Deep Should Soil Be For Herbs?

Question: I’m worried about the soil depth for my herb gardening space. How deep should soil be for herbs? -Ken R.

Answer: All herbs that are grown in containers need a pot that’s at least six inches in diameter. Also, consider how large the plant will be when it’s mature so that you don’t have to transplant it to a larger pot during the growing season. However, all your herbs will need to eventually be transplanted into larger containers as they get bigger and outgrow the pots they’re planted in.

As a general rule, move new plants into a container twice the size of the one they were sold in as soon as you get them home. It’s common for herb plants sold at a nursery or garden center to have been in their container for too long already or to be sold in a container that’s too small for the plant to thrive.

The container size your herb plants need depends on the size of that specific plant. When it comes to a container’s depth, you’ll need to consider the size of each herb plant’s root system. Average root system sizes and container guidelines for herbsare listed below.

• Dwarf varieties, thyme, and globe basil have small, shallow root systems and can be grown in six-inch pots. If you don’t want to have to water these plants so often, though, you might consider planting them in something larger.

• Most herb plants do well in eight-inch or 10-inch containers.

• Mature herbs that have grown to be relatively large need 12-inch or 18-inch pots, as do parsley, basil, and lemongrass plants. Parsley and basil have particularly extensive root systems and would be best housed in 18-inch containers.

• Whenever you’re grouping more than one plant together so that the pot will house multiple plants, use 12-inch or 18-inch pots.

• Chive has a very shallow root system that is only three inches long.

• The roots of oregano, tarragon, and thyme plants are six inches long.

• The root systems of cilantro/coriander and summer savory herb varieties average eight inches.

• Rosemary plants have root systems that grow to be around 12 inches long.