How to Prepare a New Garden Bed in Clay Soil

It’s that time of year when you want to get your garden going, but how do you turn that piece of lawn into a luscious, productive garden plot?

Unless you are that rare person who lives on a foot of pure gorgeous loamy soil, there is some prep work to be done. Many people, especially here in Kansas City, have clay soil. How do you know if you do? Gather a fistful of not too wet soil and squeeze. If it stays in a clump, you probably have a clay soil. If your soil pulls away from the side in drought, it’s clay. Never fear, you can turn that into gold.

Here’s how.

1. Determine your growing space

Be realistic with both how many plants you will need to fill a space as well as the time you have to weed and tend that garden area. More space means more plants, more soil, more compost, more water, more mulch and more time.

If you’re new to gardening start small. You want to be able to reach all the parts of bed. If you can walk all around a bed, 4’ is wide enough that you can reach into the middle. Make it less than 3’ if you’re against a wall or fence.

Organic shapes with curves may be nice, but remember you need to think about the edges and how you will keep them weed free. Straight lines are easiest.

After you mark out your space, mow it down as close to the ground as you can.

2. Get a soil test

This is recommended, but most new gardeners won’t do this and that’s ok. If you’re more experienced and serious about your garden, give it a try. I use Logan Labs in Ohio because they tell me what micronutrients my soil needs. You can also use your state extension office to give you basic N-P-K results and pH levels. Logan Labs turns the results around pretty quickly.

3. Add compost and amendments

Based on your soil test, add any amendments such as sulphur, lime, boron, etc. Even if you didn’t get a soil test, but you have clay soil, ADD COMPOST. In Kansas City, I can find most amendments at Suburban Lawn and Garden or on Amazon.

Here’s the thing with clay soil: in many ways, it’s wonderful. It’s usually chock full of minerals that’s great for plants. It has great cation exchange capacity or CEC which is the ability to move those things around. But, what clay doesn’t have is air pockets and roots need air to grow just like us. We fix this by adding organic matter via compost.

Now, not all compost is created equal. If you go and get compost from your local municipality for free, it might be full of bark and not totally “digested.” How do you know if your compost isn’t finished? It is still releasing steam and feels hot to the touch. If this is all you can get, go for it. It’s better than nothing.

Most compost sold at garden centers isn’t much better than the free municipality compost because it’s also made from yard waste. Some places test their compost and add things to it. Ask. In the Kansas City area, I have been to KC Compost in Belton, Missouri Organic (not my favorite), and Suburban Lawn and Garden.

You can also go to the KC zoo and get their composted vegetarian animal manure. It takes time and you have to schedule it. Look for the “Zoomanoo” on the website. It's also high in phosphorus, but is still a great one time addition to your garden. Manure has the added benefit of active biology. Live soil is healthy soil. I’ve used this and found plants love it.

You can also add pine bark soil conditioner which introduces organic matter to your soil and more air space. Suburban Lawn and Garden sells this as do other shops.

The chunkier the material, the longer it takes to digest and may tie up nitrogen in the soil to break it down, but you can add nitrogen through feathermeal or other organic fertilizers to add it back in. I have found that my clay soil is so hungry for organic matter that it seems to gobble it up quickly.

Add 2-3 of inches of compost to the top of your bed. No need to overdo it.

Whatever organic matter you choose, TILL IT IN. Clay is so solid, if you just lay it on top, it will take a while to work into your soil. However, if you till it in, you’ll jump start that process.

You can rent tillers at most hardware stores or check facebook marketplace for people to come till larger plots. I prefer smaller, more manageable tillers. I also prefer rear-tine tillers to help deal with hard soil with rocks in it. I love my little Mantis because it kicks up good sized rocks. I only till like this once when I form a new bed. Till down about 6-8” if possible and mix the native soil with your compost like brownie mix. No tiller? Shovel, shovel, shovel.

I don’t fuss with smaller rocks, but larger ones that will block roots come out at this time. You might need to dig them out with a shovel. Consider it a free workout.

Once you till, shape your beds with a garden rake. This is a great time to mound up your growing space into raised beds and define your edges. Raised beds are great for allowing water to drain away from the roots.

4. Kill weeds

When you till, you bring up a ton of weed seeds. Rather than using chemicals, tarp your newly formed area with a heavy plastic and weigh it down so that the plastic sits right on the soil. The plastic can be clear or opaque. The plastic catches the heat and kills any seeds that germinate underneath. Leave the plastic on for about 6 weeks. Don’t have six weeks? Skip to step 5 and keep reading.

5. Add Biology

You’ve added organic matter which adds air space, but it’s actually there to feed good soil bacteria and fungus. Living soil is healthy soil. Once you are ready to plant, add biologically active products such as Elm Dirt’s Ancient Soil to your bed at this time. Are you an avid DIYer? Try starting a worm bin and making your own worm tea or looking into JADAAM and Korean Natural Farming to create your own biologically active products. There are books, podcasts, and youtube videos about this. You can find the Ancient Soil in my shop.

6. Plant

Now comes the fun part. Plant your plants! You can add a general organic, balanced fertilizer at this time. I recommend Elm Dirt’s Plant Juice found in my shop for even more biology on your plants and in your soil. Water your plants in well when you plant. If you can use rainwater, even better.

6. Mulch

A bed I made last fall and mulched with chopped leaves. The bulbs are peeping through and there are NO WEEDS.

Don’t skip this step! I know you did a lot of work already to get to this step, but if you don’t mulch, you will regret it all season long. You can use wood mulch, fabric, rocks, straw, leaves, pine needles, or whatever else you have available. Make sure it’s a thick enough layer so that the weeds can’t push through—at least 3-4”. You may need to make space around little seedlings.

I avoid dyed mulch and use wood chips from a tree service I trust. This adds even more organic matter to your soil that will eventually be incorporated into the soil.

Mulch suppresses weeds and keeps moisture in the soil.

7. BONUS: Add Irrigation

Whether you set up drip irrigation or sprinklers, irrigation saves a lot of time on watering throughout the season if you have more than a small growing area. My favorite drip irrigation source is Drip Depot online. They have tons of kits and helpful videos to show you how to do this.

There you have it. Take that patch of clay-ey, rocky soil and turn it into a gorgeously productive garden bed. You’ll find that hard soil turn into a beautiful alive soil that supports your growing with vigor.

I know it’s a lot of work to get a new bed prepped when you have soil like this, but once you do it and set a good foundation, it will reward you for years to come.

Happy growing!