Deciphering the Correct Seed Planting Depth: A Step-by-Step Guide

The right depth at which you plant seeds increases the chances that they will grow into strong seedlings, and also increases germination. The depth will vary depending on your seeds’ size and type. While seed packets will always give you a recommended depth for planting, we may lose our packet with the detailed instructions or receive seeds that are missing those instructions. Then we’ll need to know how deep to plant the seeds in seed-starting soil or garden soil.

Planting Depth: General Advice
Common gardening wisdom says that you should not plant a seed more than twice the diameter of its diameter. Many small seeds are too big to be planted at the “quarter-inch” depth recommended on seed packets.

Seed Company Websites: Information
You can find the variety of seeds that you are using on the websites of major seed companies. Sites often include details about the depth at which to plant seeds along with descriptions of the seed varieties they sell. You can gain insight even if you do not know the variety of seeds you have. If your neighbor gives you bush bean seed, you can look up bush bean varieties on the website of a seed company and get a good idea about how deep to plant them.

General Guidelines for Seed Depth
Here are some tried and true guidelines to follow if you cannot find the recommended depth of planting for your seeds on the internet:

In general, you should plant seeds at a depth that is two times their width or diameter. If you have a 1/16-inch seed, then it should be planted at a depth of 1/8-inch. It may be necessary to plant large bean seeds that are up to half an inch wide.
Place tiny seeds on top of soil, and cover with vermiculite or soil.
Do not compact the soil on top of the seeds when you are planting them. The soil should not be compacted but it should be firm.
Covering Seeds with Soil
Most seeds including familiar fruit and vegetable seeds require soil to be covered.

Brassicas (broccoli, cabbage, cauliflower)
Seeds that Should not be Covered
Some seeds require light to germinate. Place them on top of the soil, and gently press them to ensure that they are in contact with it. You should not cover the seeds with soil. These are small seeds and few are suitable for vegetable gardens. Some examples include:

Ornamental Peppers
Sweet alyssum
The Problems of Planting Too Deep
The tolerance of large seeds to being planted too deeply is higher than that of tiny seeds. Planting too deeply can lead to limited or no germination, and weak seedlings. Double-check your recommended planting depth or plant slightly shallower next time if you experience any of these issues.