How to Plant and Grow Tomatoes in Clay Soil

When you want to grow tomatoes but the soil in your garden is sticky and lumpy, is there any way to meet your goals?

You’ll be happy to know you can grow tomatoes in clay soil!

A close up vertical picture of rows of tomato plants growing in the garden, surrounded by straw mulch at the base of the plant and a cage for support. To the center and bottom of the frame is green and white text.

But let’s put a couple of qualifiers on that statement.

You can succeed, but achieving success will be more difficult than it is for your fellow gardeners who are growing in easy-to-till loam. Hard, heavy earth is never going to be anyone’s first choice of growing medium for these stars of the vegetable garden.

To produce that juicy, satisfying crop you’re looking for, take it from me, there’s going to be a bit of extra work involved.

Particularly the first time out, you’ll need to pay careful attention to amending the soil, and put in the extra time to make sure it doesn’t hold so much moisture that it waterlogs your plants.

A close up of ripe red tomatoes hanging from the vine on a soft focus background.

To succeed in these growing conditions, you’ll also need to be vigilant throughout the growing season.

I’ve taken this approach and followed the tips and practices outlined here many times myself, in my years of living in an area with heavy (not quite clay, but similar) dirt. So I will start by telling you about two simpler alternatives.

But for the enthusiasts who really want to dig a garden in their clay soil and grow tomatoes there, I’ve got some solid (pardon the pun) advice. Follow along if you’re up for the challenge.

Here are the topics I’ll dig into:

Two Simpler Alternatives

Not quite sure you’re ready to go all in and tackle that clay?

First, you can opt out of coping with the inhospitable earth altogether by choosing to grow your crop in containers, in raised beds, or square foot gardens, with soil and amendments that come from suppliers in your area rather than your own yard.

A close up of a hand from the right of the frame planting a small seedling into rich soil in a raised garden bed made from wood.

Or, you can work around the hard, sticky garden dirt by building an open-bottomed raised bed on top of your garden, and filling it with a healthy balance of topsoil, compost, peat, and other amendments that will improve drainage and make nutrients more readily available.

When you grow tomato plants in that type of garden bed, their roots will eventually come into contact with the dense earth beneath. But there’s a good chance it will soften by the time that portion of the growing season arrives.

As for growing directly in clay, the time has come. Let’s get to it!

Why It’s Hard to Grow Tomatoes in Clay Soil

If you’ve never tried to grow vegetables in heavy, sticky dirt, you may not realize how tricky it can be.

A close up picture of clay soil that has dried out and is cracking.

For one thing, the second it rains, this type of earth forms slimy clumps. They’re heavy and just about impossible to dig, even with a newly sharpened spade.

As for dry clay, well, it’s the same as hard ground. It compacts in ways that make it hard for seeds to sprout, or roots to seek water.

Seedlings can get trapped in this hardened earth and snap at the base. A plant’s roots may simply stop growing when they can no longer puncture the heavy mass.

Clay soil does have at least one redeeming quality:

It is chock-full of valuable nutrients that can make tomatoes highly productive – if you can follow the gardening techniques that make these nutrients accessible to the plants.

To minimize clay soil’s negative tendencies in favor of that rich source of nutrition, you’ll need to amend, mulch, and manage irrigation throughout the growing season.

Taking these steps will significantly increase your odds of harvesting a juicy, red (or green, purple, yellow…) crop of tomatoes at season’s end.

Why You Should Test Clay Soil

So many fellow gardeners will commiserate when you say you have only heavy, sticky ground for a garden. (I’m one of them. While my area doesn’t feature standard red clay, I do garden in soil that’s dense and dries into hard clumps.)

A close up of a hand from the left of the frame wearing an orange gardening glove holding a handful of soil, with a garden trowel to the right of the frame and soil in the background.

But not all clay soils are created equal, so it’s important to test yours before amending it to grow tomatoes.

Tomatoes like a pH between 6.0 and 6.8, slightly on the acidic side.

To make sure your growing medium is at that pH, establish your baseline pH with a test instead of just making assumptions. You can learn more about soil tests in our guide.

A test might also indicate that you need to add calcium before planting. A good option there is gypsum, because it boosts calcium while loosening those sticky, red particles.

Gardening expert Mike McGrath also recommends saving eggshells, drying them, crushing them to a powder, and adding this to the planting hole. You can read more about it in his book, “You Bet Your Garden® Guide to Growing Great Tomatoes.”

You Bet Your Garden® Guide to Growing Great Tomatoes

The second edition of this helpful tome was published in January 2020. Copies are available from Amazon and Barnes & Noble.

But don’t start making amendments without test results. If your dirt doesn’t need more calcium, adding it will upset the nutrient balance of the soil.

Amending Dense Dirt

If you don’t have firsthand experience growing tomatoes in clay soil, this might surprise you:

  • At no time should you till that type of garden dirt l before planting.
  • Tilling only makes the whole garden area resettle into a hard, dry mass.

Instead, you’ll want to take entire sections of the dense dirt right out of the ground and replace each with a more suitable mix of topsoil, compost, peat, manure, and other amendments.

A close up of two hands from the left of the frame holding a garden shovel digging out dense clay soil.

There is more than one way to go about this soil boosting process. I like the approach of digging out little sections for each tomato I intend to plant.

Rotate Your Crops

If you’re planning to grow tomatoes every year (and why wouldn’t you?), anticipate amending the soil in several different garden spots over the course of the next few seasons. This is tougher when all of your available garden space has dense earth, but it’s essential.

Tomatoes should be rotated to a new spot after the first year, and not planted again in the same space for two seasons after that. This crop rotation helps prevent soil-borne diseases and discourages the proliferation of insect pests that prefer one type of crop over another.

The good news is that you can still plant other vegetables in that hard-won aerated earth. Just make sure to choose brassicas, legumes, or cucurbits to follow tomatoes – or other nightshades – in your garden, and rotate them the following growing season as well.

Since you’re starting with tomatoes first, make sure to choose a site that receives the eight hours of full sunlight they require.

For each plant, use a high-quality spade that’s clean and sharp, and dig up a plug of soil that’s about 16 inches wide and a foot deep. Space these holes at least two feet apart.

Put a couple of inches of wood shavings across the bottom of each hole. You’ll need to make sure they come from wood that’s not treated or sprayed with pesticides.

Also avoid walnut wood shavings, since they produce juglone, a toxic chemical that will kill your tomatoes or anything else you try to grow.

But natural, untreated wood shavings will prevent water from accumulating in the dense clay below the amended soil. The layer acts like an absorbent towel, retaining moisture without allowing it to pool.

A close up of two hands from the left of the frame wearing yellow gloves, placing a seedling into a hole in the soil, pictured in bright sunshine on a soft focus background.

Also, be sure to add extra nitrogen to the mini-gardening holes if you switch to growing another vegetable in the same spot next year. Wood shavings tend to leach nitrogen from the soil.

That’s okay for tomatoes, which thrive in slightly acidic soil, but other vegetables might react poorly to the lack of nitrogen.

Once you’ve completed the layer of wood shavings, fill each hole with equal parts organic compost, composted manure, and topsoil, along with any amendments like wood ash or gypsum that were indicated by your soil test.

Mix all these components lightly with your hands or a garden fork. This mix is nutritious and also offers the aeration the roots need to thrive.

Within these amended soil basins, you’ll dig another hole that’s about six inches deep to plant your seedlings. For the scoop on this part of the process, check out the planting section of our guide to starting tomatoes from seed.

A close up of two hands from the left of the frame carefully placing a small tomato seedling into thick, dense earth.

If you like, you can also make a few larger basins using the same layering concept, and then grow two or three plants in each one. Be sure to give them plenty of room to spread – most cultivars grow into large plants!

Whether you go for the multi-plant or individual basins, make sure to work some sand or silt into the top three inches of any dense dirt that surrounds your planting areas.

Mulch them when you mulch the basins where the tomatoes are growing, and soon all the compacted earth near your plants will begin to soften a bit.

See our guide for more tips on understanding the soil in your own backyard, whether clay or any other variety.

Staking Tomatoes in Clay Soil

It may seem overly optimistic to “plant” a stake at the same time you plant the seedlings, but it makes good sense.

A close up of a wooden stake pressed into the soil to support a young tomato plant growing in the garden, pictured in bright sunshine.

You want to stake while the ground is still soft and accessible. Make sure to determine just how tall your bush or vining variety will grow before selecting appropriate stakes, cages, or trellises.

Mark a spot about eight inches away from the center stalk of each transplant, and pound each support about 10 inches deep into the ground. Be sure to watch the plants as they get taller and start to spread, making sure that each one still has ample support.

Learn more about staking your tomatoes in this guide.

When to Mulch

I recommend mulching to retain moisture and prevent weeds from growing.

When you grow in clay, the mulch also helps to prevent rainwater from pouring through the peat, compost and other amendments you’ve added and pooling on top of the clay at the bottom.

A close up of a garden fork from the left of the frame placing straw mulch around the base of a plant growing in dry, dense soil with a small metal cage for support.

And mulch is an absolute must for keeping the garden bed from drying out, because any of the clay in your growing mix will become dense and compact if it’s not nice and moist.

Do watch for slugs and snails, because they like to hide away in mulch by day and then slither out in the dark to eat holes in your precious fruits. To keep them at bay, consult our guide to protecting your garden from slugs and snails.

What to use for mulch is up to you. Straw is always a good option, or you can use mulch paper sold by suppliers including ARBICO Organics. Newspaper is okay, too, as long as you steer away from glossy circulars or multi-color ink.

Start with a heavy layer of whatever you choose. Check out our guide to mulching and low maintenance gardening for more information.

A close up vertical picture of a tomato plant surrounded by straw mulch pictured in bright sunshine on a soft focus background.

Mulching is not a one-time thing when you live in clay-soil country. You should start with several inches when you plant, and replenish whenever the layer gets lower than that.

As the organic matter in your mulch of choice breaks down during the growing season, it will loosen the clay. You can cover your bed in leaf mold, grass clippings, or hay, too.

This will keep the dirt from compacting during winter rains or snowfall. Read more about mulching in the wintertime here.

Special Watering Tips

If you’ve stuck with me this far, you’re probably getting the idea that it’s going to take a bit of extra work to grow tomatoes when you have clay soil.

A close up of a man standing on a path between two vegetable raised garden beds holding a metal watering can and watering the base of a tomato plant.

It is, yes. But do remember that the payoff is worth every bit of mulch you tote in the wheelbarrow, and every particle of wood ash you stir into the planting holes.

All of these efforts together yield homegrown goodness. And if you live in an area where everyone’s soil is made up of clay, I’m betting those delicious, juicy, fresh from the garden fruits are hard to come by.

Even if every store stocks them, there’s no taste like that of your own garden-fresh tomatoes. Remember this payoff when you’re watering your plants!

A close up of a young seedling surrounded by straw mulch being watered from above on a soft focus background.

This chore starts with a couple of inches for the new transplants, usually a couple of cups of water apiece.

And then you’ll need to make sure these garden areas stay moist but not waterlogged for the rest of the growing season.

If it gets too soggy and then dries out, your dirt could crack, which may expose the tomatoes’ roots and make it hard for the plants to draw nutrition from the soil or stay hydrated.

Or, worse yet, wet clay that dries completely can form dense lumps at the bottom of your amended planting area. Those hunks of clay will prevent the roots from growing any deeper, or from drawing up nutrients into the plants’ leaves and stems.

The Easiest Way to Grow Tomatoes in Hard Clay Soil

As a parting thought, I want to encourage my fellow gardeners contending with heavy soil to recognize the rewards that go beyond harvesting at season’s end.

A close up of small tomato seedlings growing in dense soil amended with organic material.

Having hard dirt instead of the type that you can till with a kitchen fork and weed with ease gives you a chance to persevere and come out on top.

It’s especially soul-satisfying to try to grow what you want with what you’ve got, even when your area’s sunlight, season length, or, yes, soil, aren’t ideal.

This time, maybe you’re trying to harvest a bounty of tomatoes from inhospitable soil. Next time, maybe you’ll be attempting to grow sunflowers in part shade, or broccoli in a short spring, or any number of other “make-do” gardening projects.

If you fail, you can always tinker and tweak and try again. And when you succeed, wow!

While we’re on the topic of success, how about sharing your tomato-growing secrets in the comment section below?

And if these tips were helpful, you might be interested in the advice that you’ll find in some of our other tomato growing guides:


Don’t forget to Pin It!

A collage of photos showing tomato plants growing in clay soil.

© Ask the Experts, LLC. ALL RIGHTS RESERVED. See our TOS for more details. Originally published January 3, 2015. Last updated: May 9, 2020. Product photo via Barnes and Noble. Uncredited photos: Shutterstock. With additional writing and editing by Allison Sidhu.

About Rose Kennedy

An avid raised bed vegetable gardener and former “Dirt to Fork” columnist for an alt-weekly newspaper in Knoxville, Tennessee, Rose Kennedy is dedicated to sharing tips that increase yields and minimize work. But she’s also open to garden magic, like the red-veined sorrel that took up residence in several square yards of what used to be her back lawn. She champions all pollinators, even carpenter bees. Her other enthusiasms include newbie gardeners, open-pollinated sunflowers, 15-foot-tall Italian climbing tomatoes, and the arbor her husband repurposed from a bread vendor’s display arch. More importantly, Rose loves a garden’s ability to make a well-kept manicure virtually impossible and revive the spirits, especially in tough times.

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W. LePage
W. LePage (@guest_325)
3 years ago

I find your statement to remove leaves so sunlight will hit the tomatoes and they will ripen faster a bit odd. I learned in school many many years ago that sunlight results in the production of chlorophyl which I believe is the source of green in plants. Wouldn’t direct sunlight enhance the production of chlorophyl and prolong ripening? I always store pre ripened tomatoes in dark places to enhance ripening. Is this not a good idea?

Allison Sidhu
Allison Sidhu (@allison-schultz)
Admin
Noble Member
Reply to  W. LePage
3 years ago

Hi W.,

Thanks for reading! You’re right about chlorophyll- but this doesn’t affect the ripening of fruit. Heat actually helps to speed this process along, and tomatoes release ethylene gas. It actually helps other fruits nearby on the vine to ripen as well- the same process that takes place when several unripe toms are places together in a closed paper bag.

Pretty neat, huh?

You can find more information on the process that makes tomatoes turn red in this article.

Ed
Ed (@guest_1917)
1 year ago

I’ve tried this in the past and the hole fills up with water in any heavy rain storm since the clay soil doesn’t let it disperse and the plants eventually drown and rot away.

Adam H
Adam H (@guest_4255)
Reply to  Ed
1 year ago

I have had that problem a bit. I dig bigger deeper holes, like 2.5 deep by 2 feet wide. Then, after the plant grows a bit, I spread mulch about 3 inches deep over the soils.

The clay is so bad here that my crawl space sometimes floods and doesn’t drain for a week!

1BraveHeart
1BraveHeart (@guest_3728)
1 year ago

What I found that seems to work…is taking some plastic drink bottles cutting off the very bottom portion so the top is straight and push the top down into the fertilizer/mulch and whatever (like Nitrogen and other products). Now what do you have? A plastic container with a drain spout directly to the plants ROOTS…uh, ask Alex Hailey about Roots and not me….just trying to be politically correct (don’t you see?)…anyways….a source to keep those roots wet….but don’t ever forget those healthy watered plant roots can NOT penetrate cement like soil in the hot, summer time…when the tomatoes should be… Read more »

Ted
Ted (@guest_4292)
11 months ago

Hi this is my first time having a garden I planted from the sides 45 tomatoes and 12 peppers in my garden that has clay type soil. When I started the garden I shaved the grass off then I flipped the soil over to make sure the weeds will not come back. I planted the seed of tomatoes and peppers in the house. One and a half weeks later I planted them in the garden. Now, 2 months later, the tomatoes are 2 to 3 feet tall with 🍅 on them, flowers and blooms. Most of my tomatoes have one… Read more »

Allison Sidhu
Allison Sidhu (@allison-schultz)
Admin
Noble Member
Reply to  Ted
11 months ago

Sounds like you’ve made good progress so far this season. Do you know if you are growing determinate or indeterminate type tomatoes? Determinate plants are usually smaller when mature, and they will produce a single harvest with fruit that ripens all around the same time. Indeterminate types will continue to grow throughout the season, with a continual harvest. Rather than letting them spread on the ground, they should be staked in some way that will allow them to continue to grow taller through the summer. I’m not sure exactly what you mean re: the big, funny-looking tomatoes. Can you attach… Read more »

Tom H.
Tom H. (@guest_4845)
9 months ago

I save egg shells, dry them out, grind them up, then add them to soil for calcium.

Also, if I do the inverted tomatoes I like to hang them on the south side of the brick house. I have harvested tomatoes as late as November, in Detroit, Michigan that way, because of the heat to the plant during the day and the bricks give off warmth at night for a longer growing season.

Lynne
Lynne (@guest_7715)
Reply to  Tom H.
7 days ago

I have found many Cafe cooks will save egg shells for me. I give them a bucket with my name and number but I go back in no more than a week. Morning cooks of course, go through a ton of eggs.

Melody Engle
Melody Engle (@guest_6238)
1 month ago

When it rains our ‘clay hole’ fills with water and generally retains the full water hole for two days after the rain. Is this bad for the tomatoes and what do we do about it?