We had a good question come in to the Square Foot Gardening Foundation recently and thought it would be helpful for everyone.
“Do I ever need to change out the soil mix (Mel’s Mix) in the containers completely? How do I amend the soil each year?”
Mel’s Mix components. Clockwise from top: compost, peat moss (or coco coir), and coarse vermiculite.
This is a great question because if you’re used to growing in something other than Mel’s Mix you have to do a lot more work and amending. Switching to Mel’s Mix is definitely a change, but a good one!
Let’s investigate how Mel’s Mix works and why you don’t have to replace it constantly or amend it.
First, we’re going to assume you’re using Mel’s Mix as prescribed in the All New Square Foot Gardening book which is, by volume,
- 1/3 peat moss (or coco coir)
- 1/3 coarse vermiculite
- 1/3 of a good blended compost made from at least 5 different sources, if possible or use your own homemade compost, which we recommend
Second, we’re going to assume that if you are using Mel’s Mix that the only thing you’ve added to your Square Foot Garden when you replant is a trowel of compost each and every time you’ve harvested a square — it’s that easy!
Our advice is to not mess with success. . . so, if this is not what you’ve been doing, say you’ve added other potting mixes or your native soil to your garden bed, you probably will need to amend your soil, have it tested, add artificial nutrients, and so forth. It would be simpler to start over using Mel’s Mix.
Extending the life of your Mel’s Mix throughout the Season
To make sure your Mel’s Mix lasts for at least 10 years, always mix in a trowel of compost once you’ve harvested a square’s veggies and removed its plants. This will naturally refresh the nutrients in the Mel’s Mix.
When you harvest a square mid-season, or at the end of the season when you’re cleaning your beds, knock off as much of the Mel’s Mix back into the square as possible. The stubborn bits of Mel’s Mix clinging to the roots can be swished in a bucket of water and then used to water your garden.
Of course, no matter how diligent you are, after a few seasons of being absorbed into the plant roots, you’ll notice that the level of your Mel’s Mix will naturally go down. When you lose an inch or two, you’ll add more fresh Mel’s Mix mixed in the proportions described above. You’ll incorporate this into the older Mel’s Mix. This will help bring up the proportion of peat moss and coarse vermiculite and keep your mix loose and friable.
Amending the Soil – Is it necessary?
You do not need to amend Mel’s Mix each year – that’s done on a continual basis throughout the gardening season when you add compost. If you choose to not grow beyond the summer season, and put your beds to rest over the winter, many SFGers put dark plastic sheeting over the raised bed and weight it down. By doing this, your beds will be ready super early the next season.
Learn more about the Square Foot Gardening Method by taking the introductory course.
