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Why Mulching with Compost is the Shit! (Pun fully intended.)

Updated: Apr 1, 2020

Last week I released a free Spring Garden Checklist to help you know what you can do to prepare your garden for the growing season. If you haven’t downloaded yours yet, go here, you won't be sorry!

Listen, there were A LOT of steps to check-off on that list. Spring really is the busiest time of the year for most gardeners. My goal isn't to overwhelm you, but to get your wheels turning and give you the best head start to the gorgeous and productive garden you've been dreaming about.

But what if you could only prioritize doing one of those tasks this Spring? That's easy! I would urge you to mulch your garden. I know, I know...probably not the most glamorous response you were hoping for, but bare with me.

I want you to mulch your garden. And to be more specific...I want you to mulch your garden with compost.

Before anything else you learn as a gardener, I want you to always remember that your first priority is to preserve and improve soil health. And the single best way to do that is with compost.

What's Mulch?

Mulch is any material used to cover exposed soil. There are a lot of products in the gardening landscape that are marketed as mulch from shredded rubber (a byproduct of recycled car tires) and plastic sheeting to bark chips and shredded leaves. As you can imagine, not all mulches are created equal in the organic garden. Any mulch coming into my garden must meet some stringent requirements for use.

My Criteria for a Good Mulch

My mulch must:

  1. Feed the soil. Good organic mulch does the important job of feeding the soil food web by adding organic matter to the soil. Beneficial microbes and insects like earthworms break down that organic matter, and nutrients are unlocked for plant roots to uptake and the mulch particles are distributed to the top layers of the soil. No tilling required! If you want to nerd out on what all those cool microbes and insects do in your soil I highly recommend reading Teaming with Microbes by Jeff Lowenfels and Wayne Lewis. It really set me on a path toward no-till organic gardening, and I haven't looked back since then. Healthy soil should consist of around 30% organic matter and there are very few places on our modern earth that naturally meet that percentage. Here in Western Nevada County, our soil is predominantly clay, and because of that, it is sorely lacking in nutrient density and ideal soil structure for vegetable crops. So regular mulching is high on my priority list to add nutrients, create a healthy soil food web, and improve my soil structure.

  2. Suppress weeds. A study by Ohio State University Extension suggests mulching 2 -3” deep will drastically suppress most weed seeds. Since weed seeds can remain viable for several years, covering them with enough mulch to keep out sunlight is the best prevention method you’ll have. It also means a heck of a lot less work for you in weeding chores.

  3. Suppress soil-borne diseases There are many diseases that can come from soil that can plague our edible gardens. Tomatoes and fruit trees are two I hear the most about. Fungal spores from the soil can be splashed up onto the plant during rain storms or overhead watering allowing the pathogen to infect leaf or bark tissue. Covering the soil with a protective mulch layer prevents splash back from happening, effectively cutting your risk of soil borne diseases drastically.

  4. Be Pretty Seriously, there is nothing quite like a fresh layer of dark mulch to make your garden look tidy and really make your plants shine. For this reason I don't tend to gravitate toward plastic mulch sheeting or cardboard.

  5. Protects Soil Surface from compaction and erosion from rain and wind Did you know that erosion and soil loss has become one of the biggest issues facing agriculture today? According to the World Wildlife Federation the earth has lost nearly half of its top soils to erosion in the last 150 years. They say this is due to unsustainable agricultural practices combined with natural elements of sun, rain, and wind. Protecting our valuable resource is essential to the health of our planet and food system. When not protected, lost topsoil is being carried into our local watersheds and wreaking havoc on our aquatic ecosystems. So keeping out topsoil in place is of vital importance for us all.

  6. Retains Water By adding organic matter to the top of the soil, you are doing a great job in protecting the soil surface from sun exposure and thus drying out. It’s like a natural insulator for your soil and will help to reduce the amount of water your plants require, a fact that is especially helpful in the heat of summer! By protecting the soil surface from baking, hot sun, you are preventing the top layer of soil from crusting over and completely drying out. And dried out soil is a lot harder to rehydrate than soil with even a little dampness to it. Think about how long it takes to rehydrate a bone-dry sponge rather than one that is even slightly damp.

  7. Keeps soil temperature cooler Did you know that most of your plants’ feeder roots sit in the first few inches of soil? They do the lion’s share of nutrient absorption. A few inches of natural mulch protects those important roots from extreme temperatures and stress.

  8. Reduces Landfill Waste I want a mulch that helps reduce landfill waste. By using composted wood, soiled stable bedding, and/or leaves, I know that I’m recycling a natural product that would have otherwise been considered trash. I also try to buy in bulk whenever I can to reduce the number of plastic soil bags I bring home, but more on that later.

Thankfully, there is something that easily meets all of my requirements and that is good compost.

What is Compost?

To simplify, compost is decayed and broken down organic matter. My compost piles typically start with layers of green weeds, grass clippings, and vegetable scraps sandwiched between layers of dried leaves and soiled straw from my goat barn. Through an alchemical change brought on with water, air and microbes, those layers of large organic matter are turned into a beautiful, black soil-like compost. It's a thing of beauty.

Compost can be made up of a lot of different ingredients, but it must have a proper ratio of ingredients high in nitrogen (i.e. manure and vegetable scraps) and ingredients high in carbon (i.e. wheat straw and shredded paper). Home gardeners can easily make compost with kitchen scraps and shredded paper. On a larger scale, compost companies make it from animal manure or vegetative refuse and straw or shavings.

Nitrogen + Carbon + Oxygen + Water + Microbes + Time = Compost

Should you make or buy your own compost

For now, probably both! While I think it’s important that everyone, especially gardeners, create their own compost, the process of making compost takes time and space. And usually the amount we can make at home cannot make the sheer volume most gardens require, but that doesn't mean it's not beneficial to make your own.

At my house there is no way I would be able to create enough compost from my own green waste (e.g. kitchen scraps, weeds, and plant prunings) and brown matter (e.g. soiled straw from my goats or fallen leaves) to mulch all of my garden spaces. But, I still produce about one cubic yard of compost each year and use it proudly wherever I can. Maybe in time I will get to a point where I'm a 100% closed system, but right now I have to purchase my compost in bulk in the Spring and Fall to get the job done.

Buying Bagged or Bulk Compost

There are a few things to consider when choosing to buy bulk or bagged compost.

  1. Amount of Compost Needed - The general rule of thumb is if you need more than 27 cubic feet of soil, then it is usually less expensive to buy in bulk.

  2. Garden Location - While I prioritize bulk mulch for my gardens for several reasons, some gardens are located where wheelbarrow or cart access is simply not an option. This is when bagged compost or soil can be immensely helpful as its easier to carry from one spot to another like down stairways or steep slopes.

  3. Physical Ability - Moving wheelbarrows or garden carts full of compost from one place to another and then shoveling it into your garden beds is a great workout. While it can be time consuming, I find the work enjoyable and a great way to move my body. However, I realize that doing that type of physical labor might be out of the question for some gardeners. And that is totally fine! This is where bagged compost and soils can be a great solution.

Where to buy compost


If you are going to go the bulk route. You can find landscape supply companies that sell soil and compost by the yard. Ask your local garden center or Google "Lanscape Suppliers Near Me" to find out who you can buy your bulk compost from. I love supporting local businesses, so this is usually the route I choose. We have a few wonderful companies in town that offer pick-up or delivery of bulk soil and compost. Most pick-up trucks can handle 1 cubic yard of soil or compost. The compost I usually buy costs about $52/cubic yard. Not too shabby compared to the bagged compost I like which would total $108/cubic yard for 9- 3 cubic foot bags.


There are a lot of wonderful companies out there that sell excellent compost in 1 cu. ft bags up to 3 cu. ft bails. I’ve used and loved the Gardner & Bloome Soil Building Conditioner ($12 for a 3 cu ft bail) and it’s pretty readily available at most garden centers. Remember that by opting for bagged compost you will be paying a higher price for the convenience of ease of transport.

When Do I Apply it and How much?

There are two times a year that I highly recommend mulching your garden.

In Spring just as plants are waking up and you’ve done your first big weeding of the season. The sooner you get the ground covered, the better, because you're covering up any dormant weed seeds which will reduce your work load in the summer time! Plus, it makes your garden beds look gorgeous. Trust me on this. Nothing makes you look like a gardener who knows what she’s doing than a freshly mulched garden bed.

In Fall. Usually I time my fall compost mulching when I’m pulling out my summer vegetable garden and planting my cool season crops for late fall and winter. Fall is the perfect time to recharge the soil from all those heavy feeders like tomatoes, peppers, and squash. Plus, you are replenishing your soil’s protective layer and getting the garden ready for lots of rain and snow. I like to think of it as putting the garden to bed with a cozy blanket.

Really there is never a bad time to add compost to the top of your soil. You should always try to mulch with compost if your soil is becoming more exposed as your mulch breaks down or if you are noticing some disease or extraordinary pest pressures on your plants. Stressed plants are magnets for disease and a good dose of compost can go a long way to remedying a lot of those issues.

Think about compost like a probiotic supplement for your soil. When your soil food web is out of whack, adding in a healthy dose of compost introduces more of the good guys to the fight.

How to Calculate the Volume You'll Need

My planner, full of garden bed dimensions.

Calculating soil volume can get tricky pretty fast when you have a lot of different garden bed sizes to calculate, but thankfully there are several free virtual tools you can use to find out exactly how much compost you’ll need.

  1. Measure the length and width of spaces you need to mulch. For my raised veggie beds it was easy. I know they are 4’ x 8’. But I’m also mulching several cut flower beds, so I took my handy dandy measuring wheel and my garden journal to take notes about the length and width of each garden bed. If you don't have a measuring wheel, a measuring tape works just perfect too. Don't have a measuring tape? You can also count your paces for a rougher estimate.

  2. Decide on mulch thickness. Remember, university studies have shown that mulching 3" deep shows drastic weed reduction. For my flower beds in the landscape I will calculate my volume based on 3" mulch thickness. For my raised veggie beds I knew I needed a bit more than 3" because my soil has sunk or compacted between growing seasons. Usually they need a top-off every growing season. This Spring I’m adding about 6” to all of my veggie beds, but only because I did not fill them in Fall like I should have.

  3. Calculate soil volume. Volume is length x width x height. Rather than doing the conversion from feet to inches. I am lazy and use an online soil volume calculator so I know I'm ordering the right amount of compost. I love this one from Gardeners Supply If you are buying your compost in bulk, usually the employees at the supplier are more than happy to check your math for you.

How to Know You're Buying Good Bulk Compost

  1. Buy local whenever possible.

  2. Talk to fellow gardeners or your favorite garden center about which supplier they prefer. Can you find 2 gardeners who have used the compost with good results?

  3. Does the supplier ensure that their compost materials come from sources without persistent herbicides? Persistent herbicides are sometimes used by hay and grain farmers and don’t break down during digestion or decomposition. In fact, they can remain in the soil for years. Affected manures, hay, and straw carry these herbicides into the compost you carry into the garden, which can have devastating effects on the lovely vegetables and flowers you are trying to grow in the garden.

  4. Does the compost look, smell, feel finished and alive? Good compost should be dark in color, smell earthy and feel cool and damp. It SHOULD NOT smell sour or funky like sulfur or ammonia. It should not feel dry or dusty. And lastly it should not feel hot. Hot compost means that the microbes inside have not finished their work digesting the ingredients yet.

How NOT to apply compost to your garden.

Rather than talking about the process of spreading 2 - 3" of compost to your topsoil, which is pretty self explanatory. I want to show you what NOT to do with your mulch. Mulching like this can actually cause a lot of problems for your trees and shrubs and potentially even kill them.

Volcano Mulch

Volcano mulch happens when a whole bunch of mulch is dumped directly around the trunk of a tree or shrub. Please don't do this! What volcano mulch does is suffocate the base of the tree and allows pest a safe place to burrow into the trunk or introduce rot.

Instead, when you are mulching around your trees and shrubs, you'll want to make sure that the mulch is not touching the trunk. Instead, spread your 2"-3" layer of mulch around the drip line, where the feeder roots live. Think of the drip line as where the leaves of the tree or shrub would fall to the ground, basically under the leaf canopy.

Doing This Task in My Garden

Next week 10 cubic yards of compost are being delivered to my house. That is going to be one giant pile of compost! So if you need to find me this week, you know where I'll be...outside working on my sweet gardener bod and getting my garden ready for all the veggies and cut flowers to be planted once the weather warms up a bit more.

I can't wait to see how you apply this step! Tag me on social media and use the hashtag #revivalgardenlist as you do your Spring garden chores so I can cheer you on! Leave me any questions or comments you have about mulching or compost in general. I'd love to help you. In the meantime, happy gardening!


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