Here's Why You Should Apply Compost To Your Vegetable Garden This Fall

​It will lead to better soil health and higher nutrient levels come spring.

September 13, 2017
wheelbarrow full of compost

In most regions of the country, peak harvest season is immediately followed by a fall garden cleanup. Fall cleanups can be quite satisfying. While the end of the season always makes growers a bit wistful, it also feels great to clear out tangled and exhausted crops—to revel at the immense size achieved by such short-lived plants and to enjoy the cool breezes and changing light of of the season.

The fall cleanup also provides a time to reflect on this year’s successes and failures, and to take concrete steps that will make next year’s garden even more robust and productive. One of the best things you can do for a fruitful garden next year is to add compost now.

(Whether you're starting your first garden or switching to organic, Rodale’s Basic Organic Gardening has all the answers and advice you need—get your copy today!)

Soil health is the backbone of organic food production. The health of your garden soil is determined largely by its organic matter content and nutrient levels. Compost is the most effective amendment to supply new organic matter and nutrients to your soil; and fall is the best time of year to add compost to the garden.

Related: 5 Ways You Can Improve Your Garden Soil, According To A Soil Scientist

decomposing pile of compost
What exactly is compost?

First, it may be helpful to briefly consider what we are talking about when we say “compost”. In recent years, the word compost has taken on a range of new meanings, depending on the context. For example, it is not uncommon to hear people refer to the fresh vegetable cuttings on their kitchen counter as “compost”; and they will also call a giant pile of decayed plant matter in the backyard “compost”. Technically, it would be more accurate to call the decayed backyard pile “compost”; whereas, it would be more accurate to say that you are “going to compost” the fresh food scraps in the kitchen.

In any event, compost is a term that refers to decaying organic matter. For a garden application, the more decomposed it is, the better. Compost can include kitchen scraps, grass clippings, fallen leaves, seaweed, coffee grounds, eggshells, vegetable scraps, meat, bones, cardboard; virtually anything that was once alive. (Here are seven surprising things you didn’t know you could compost.)

Once applied to the garden, soil microorganisms break down the compost into humus, which continues to break down into usable, water-soluble nutrients. (Check out the unexpectedly adorable microscopic organisms that live in your garden soil.) Humus acts as a glue to hold soil particles together and leads to good soil structure, which allows plant roots to move effectively. Humus also helps soil maintain proper moisture levels. Without humus, water will either leach away too quickly for plants to use, or will be difficult for the plants to absorb. Humus-rich soil will soak up water and hold right where your crops can use it. Because humus is always decaying and being absorbed by your crops, it is essential to add more compost on a regular basis to replenish the supply.

Related: 7 Solutions To Your Most Common Compost Problems

handful of compost
How to choose the best compost

Compost can either be made at home or purchased in bags or in bulk. If you are buying compost for the garden, try to find out what ingredients went into the product. Generally, compost made with animal manure will provide more usable nitrogen, phosphorous, and potassium. (Here's how to use animal waste as garden fertilizer.) Compost made strictly with plant waste is still a great source of organic matter, but may yield less of these macronutrients. (Check our other tips for purchasing quality compost for your garden.)

A good compost should be dark in color; dark brown or even bordering on black. It may be a little bit clumpy, but should not have visible sticks or pieces of bark in it. In fact, there shouldn’t really be any identifiable components at all. It should be a crumbly, dark, spongy substance. Remember that the term “compost” has an elastic definition and some suppliers may use the term to describe a range of products. The compost you purchase will be incorporated directly into your soil, so make sure it has been specifically created for vegetable bed applications.

Related: How To Build The Ultimate Compost Bin

wheelbarrow full of compost
Why it's such a good idea to add compost in the fall

Regardless of the source of your compost, a fall application will provide copious benefits to the garden. The compost will act as a mulch or shield for your garden soil, helping slow the leaching of nutrients during winter months. As rain or snow fall on the beds, nutrients from this new top layer will work their way down into the soil and help prevent nutrients in the lower strata from being washed away.

Related: 6 Mistakes You’re Making With Your Compost Pile

In addition, the fall application provides extra time for the compost to begin transitioning into humus. Although temperatures are low and soil activity is slower than during the summer season, soil microbes will work on incorporating the compost. This will lead to better soil structure and higher nutrient levels come spring. Compost also provides the added benefit of tidying up the aesthetics of the garden, covering up random plant debris and helping to make the off-season garden more appealing to the eye.

Related: 8 Gardening Mistakes You Make Every Fall

handful of compost
The best way to apply your compost

Step 1: Clear out your garden

When starting on your fall cleanup, either cut down or clean out the dead and exhausted crop residue. In many situations, it is preferable to clear out residue because your old crops may be carrying pests and/or diseases. Burying these residues in the beds may exacerbate these issues the following year. Plant residue is much better composted in a controlled site, out of the garden beds. A well-managed pile of plant debris will allow temperatures to increase enough to kill pests, diseases and weed seeds. Keep in mind that, if you are making compost at home, it is essential that it reaches 160-170 degrees so that you don’t reintroduce the fungal spores and other contaminants into your garden.

Related: Your Guide To Cleaning Up Your Garden In Fall

Step 2: Test your soil pH

Once crops have been cleared, test your soil pH. Vegetable gardens prefer a soil pH of around 6.3-6.9, which means the soil is just slightly acidic. For many of the same reasons it is helpful to add compost in the fall, lime works best when applied this time of year. The winter allows it to slowly react with the soil and adjust the pH into the preferable range by the following spring. Spread lime as needed based on your pH reading, and fork it into the soil.

Related: Everything You Need To Know About Soil pH For A Healthy Garden

Step 3: Pile on the compost

After clearing your crops and adding lime, the compost application process is just the icing on the cake. All you need to do is cover your beds with 2-3 inches of high quality compost. Spread the compost evenly over the beds and rake smooth. You can apply this compost to all areas of the garden. Cover all of the spaces vacated by summer crops but also closely surround any fall or over-wintering crops that are still in your beds.

Related: How To Defend Your Soil From Diseases That Will Ruin Your Garden

Hilary Dahl is a co-owner of the Seattle Urban Farm Company, where she helps beginning and experienced growers create beautiful and productive gardens. She has worked on a wide range of projects, from small backyard garden plots to multi-acre vegetable farms. She also works in her own garden every day when she gets home. Hilary produces a weekly podcast called Encyclopedia Botanica, where she and her co-host, Kellie Phelan, discuss seasonal garden topics and share the joy of growing your own food.