What are the benefits of compost in soil?
Improves Soil "Structure":
Soil "Structure" refers to the way that particles of soil bind together. Soils with good structure or good "tilth" are crumbly and well aggregated with lots of pore spaces for water, air, roots, and microbes. Soils with bad structure are compacted and poorly joined together. The higher the level of organic matter in your soil, the better structure your soil will have. Soil structure is important for erosion control, root and water penetration, and plant and microbe respiration, among other things.
Improves moisture retention/drainage:
Very sandy soils typically have problems retaining moisture and need to be watered quite frequently for optimum plant health. Clay soils, on the other hand, have issues with drainage and can become waterlogged during rainy periods. Both of these scenarios present problems for our vegetables, and compost is the great stabilizer for both situations! The porous yet well aggregated quality of compost will help sandy soils hold onto valuable water resources and help heavy clay soils drain more quickly!
Increases population/diversity of soil microbes:
Compost is teeming with life. It is full of bacteria and fungi that are necessary to the health of your garden. Even though we never see these microscopic populations, the work they do consuming dead and decaying plant material adds humus to your soil and makes nutrients available to your vegetables! They also protect your plants from many pests and diseases. So don't neglect the microbes! Adding compost will maintain a healthy population of this all important army of garden helpers.
Increases nutrient retention/availability for plants:
Compost is an incredibly rich and stable source of plant nutrients. And unlike many fertilizers, both chemical and organic, compost releases these nutrients slowly over time. Many plant nutrients are also water soluble, so even adding them in the form of organic fertilizer doesn't guarantee that they will all get to your plants. Think of the compost you add to your soil like a savings account of nutrients. If you add a little every year your vegetables will have a steady supply of the things they need to thrive.
Maintains optimum pH:
pH is extremely important in your plants' abilities to take up and make use of the nutrients that are present in your soil. Most compost has a pH of between 6.5 and 8, an optimum range for your vegetables. So if you have soil that is too acidic or basic, adding compost will help buffer your pH!
Should I buy compost or make my own?
The simple answer is, you should make your own! If you are an avid gardener, then you are probably used to having an abundance of plant material at different times throughout the year, whether pruning perennials, mowing grass, raking up leaves in the fall, or pulling out vegetables that have finished their life, your garden is in a continuous state of both growth and decay. So gathering the spoils of your garden and letting them compost in one place is the best way to capture and recirculate the valuable nutrients, microbes, and organic matter that you have generated!
I am not going to take up the question of how to set up a good compost system in this blog post, but if you are interested in learning more, I recommend checking out the aptly titled, Let It Rot by Stu Campbell, a wonderful resource for learning all about compost, including guidance on composting at home.
If you aren't able to compost at home, buying bags of compost or ordering a delivery of bulk compost are both great approaches as well. If you are lucky, you live in a place with lots of choices when it comes to buying compost. If so, it can be overwhelming choosing the right product, so ask at your local nursery what is recommended for organic vegetable gardening. I find many compost products to have a high proportion of woody materials. These composts are very slow to break down in soil and I prefer compost that looks and feels more like soil than like barkdust. Look for compost with a dark color and a pleasant earthy odor.