Definition - What does Lean Soil mean?
Lean soil is simply soil that is lacking in much organic material. As such, it contains fewer nutrients than rich soil. For some plants, this is a requirement. For others, it can stunt growth.
MaximumYield explains Lean Soil
Soil health is an important consideration in both in-ground gardening and container gardening. However, where gardeners using containers can often benefit from using premixed soils, those with in-ground gardens are at least partially at the mercy of Mother Nature. For instance, you may find that you have lean soil. Depending on what you plan to grow, you will need to enrich it.
What is lean soil? Simply put, it is soil that lacks much organic matter. For instance, heavy clay soils have good mineral content, but lack much organic content, meaning that they are very dense, don’t drain well, and do not have the full range of nutrients required for healthy plant growth. Sandy soils can also be lean, as can thin soils over rock. Ideally, your garden’s growing medium should be roughly 50% soil and 50% decaying organic matter. This provides minerals from soil, but also nutrients from the rotting plant matter.
If you have lean soil, you can improve it in a number of ways. One of the best options is to add hummus or compost to the soil. It can be mixed in if you till the garden, or it can be layered on top and left to decay over time.
With that being said, lean soil may be a blessing, depending on what you are trying to grow. For example, if you are trying to grow flowers that are adapted to alpine growing conditions, lean soil will be a better fit for them than rich soil will be.