Yes, you can make a great potting soil mix by combining sand and compost — as long as you use the proper sand and mix the two ingredients correctly. First, make sure that the compost you are using is completely broken down by running it through a mesh screen to filter out large pieces that need to be returned to the compost pile to continue breaking down. Only use the smaller compost particles that pass through the screen, as these particles have broken down successfully and are ready for use.
Then, make sure you select the proper sand for mixing with compost. Some sands have a large lime or sodium content that will adversely affect your soil quality and can harm your plants’ ability to grow. Choose a horticultural quality sand from a gardening center or nursery only. Never mine your sand from a natural setting unless you are well aware of its mineral content, sodium levels, and pH balance.
Once you have the right sand and thoroughly processed compost, you can create a potting soil mix by combining the sand and compost together. Nutrient rich compost is an excellent growing medium, and mixing it together with sand improves the air circulation, allowing proper aeration which will allow for excellent drainage and moisture retention.
To mix the two mediums together, pour the compost into a large container until it is around one inch deep, then add an inch of sand layered on top of the compost. Alternate layers of compost and sand until you have used up your supply of both mediums. Then, mix the layers together until the mix is blended thoroughly.
If you have a clay rich soil in your garden beds, you can mix compost and sand into it to help amend it and condition it to improve its quality and make it ideal for plant growth. Clay rich soils tend to hold larger amounts of water than other soil types. Add one part sand to each 10 parts of clay soil and mix them together until the soil has a gritty texture. Then, mix the compost into the clay/sand mixture at a one to ten ratio.
The best way to mix soil mediums together is by using your hands. Tools, such as spoons, paddles, gardening forks, and sticks are useful for mixing too, but the flexibility and utility of your hands works much better for the task. While pulling materials up and down through the different levels of the soil to mix the ingredients together properly, feel around for large clumps and crush them with your fingers to help break them down into the mixture better and keep materials from sticking together. If your compost already has sand mixed into it, lower the amount of sand that you mix with your compost.
Be sure to check the pH levels of your compost before using it to amend different soil mediums or to make a potting soil mix. Checking your compost pH is important, as compost can sometimes be too acidic and can throw off the pH of the soil you are amending. If your compost is too acidic, add grass clippings to the mix until the pH levels are as close to neutral as possible.