As a home gardener, there’s nothing like biting into a homegrown veggie fresh from the garden. All winter, all I can think about is the glorious taste of my first sun-ripened tomato. However, there’s a lot of work and decisions to make between imagining the first taste and getting it.
One of the most important decisions is how deep to make your soil. This can be tricky –too shallow and your vegetable’s roots won’t have enough space to do their thing, too deep and you’re wasting money on expensive soil mixtures that hold too much water.
Like many aspects of home gardening, there is no one size fits all answer. For some vegetables, deep soil is necessary for a fully formed result. For others, a deep soil can have too high of a water holding capacity, which can cause root rot.
Keep reading for a full breakdown of how deep your soil needs to be to grow vegetables.
How Deep Should Soil Be For Vegetables?
In a perfect world, you would have the perfect soil depth for each vegetable you grow. However, realistically you’ll have a garden bed(s) with more than one type of vegetable in them. This means you have to find the soil depth that works for all of your vegetables at once.
You want about 18-20” of soil at the very least for most home gardening vegetables. This allows for good drainage and deep enough looser soil for roots to grow through easily. Most vegetables prefer a deeper soil over a shallow soil if it’s well-drained.
Because it can be difficult to dig through 18-20” of hard compacted soil, most people choose to give themselves a head start with a raised garden bed.
Normally around 11” off the ground, you only have to dig about 8-10” into the ground. Then, when you fill the garden bed with high-quality soil, you’ll have 18-20” of soil for your vegetables to grow.
Why Does Soil Depth Matter for Growing Vegetables?
If you’re new to gardening and just looking for a fun, productive summer hobby, you might be thinking we gardening fanatics are parsing details a bit too much. After all, six inches of soil can’t make that big of a difference, right?
Soil depth can make a difference in the health and productivity of your vegetables. Deeper soils tend to hold more water and nutrients for the roots to absorb, allowing them to grow stronger. Well-rooted plants grow more vegetables as they can get more nutrients needed for production.
Also, a deeper-rooted vegetable plant will be more resistant to falling over due to wind or the weight of the vegetables.
However, a deep soil that is not well-drained is essentially a death sentence for your summer veggies. A soil that does not drain well will become completely saturated with water, which causes your roots to rot. Once root rot sets in, it’s difficult to reverse the rotting process.
Soil Depth for Vegetables Chart
Here are the recommended soil depths for fifteen of the most popular vegetables for home gardeners. This is a great easy reference guide for digging your garden or building your garden bed.
I keep a chart like this taped to the inside of the lid of my seedbox. That way, I can quickly reference it before planting my seeds.
|Alliums like garlic, onions, chives, and leeks||12-18”|
Soil Depth for Vegetables Chart in Centimeters
For our friends that use the metric system, here are the recommended soil depths in centimeters.
|Alliums like garlic, onions, chives, and leeks||30-45 cm|
|Summer Squash||45-60 cm|
|Pole Beans||45-60 cm|
|Sweet Potatoes||60+ cm|
|Winter Squash||60+ cm|
Vegetable Root Depth – Shallow or Deep
If you’re wondering why some vegetables need deeper soil than others, the answer is their root depth. Some vegetables like lettuce have shallow roots and spread out wider than deep.
Others, usually bigger vegetable plants like tomatoes, have longer and deeper roots because they require more stabilization from deep roots.
Shallow rooted vegetables like lettuce and most other leafy greens can survive on as short as only 6 inches of roots. However, they produce more robustly if given deeper soil to grow longer roots.
They also don’t have short roots just because their roots are shallow. Their roots can grow to almost 2 feet long but spread widely around the plant versus deep down into the soil.
Root vegetables like carrots and sweet potatoes have deeper roots because the production is done underground. However, this is not true for potatoes.
Vegetable root depths are more precise than the soil depth suggestions, so it’s good to know for informative gardening.
Sticking with the general ranges suggested above is the best practice for digging gardens and garden beds. You don’t want to dig to the exact depth of an average root length.
In general, give your veggies plenty of space to grow and thrive. Make sure your garden beds are big enough to allow for established roots to form. It’s better to have more space than you need instead of too little.
Vegetable Growing Depth FAQ
Now that we’ve covered the basic overview of best practices of soil depth, here are the answers to the most frequently asked questions about it.
What vegetables can grow in 6 inches of soil?
A lot more veggies can grow in only 6 inches of soil than you might initially think. However, just because they can grow doesn’t mean they can grow as well as they could in deeper soil.
Vegetables that can grow in 6 inches of soil include lettuce, summer squash, cucumbers, corn, peppers, green beans, peas, and radishes.
Can you grow vegetables in 8 inches of soil?
Much like the above question, many vegetables can be somewhat successfully grown in only 8 inches of soil. However, you might see less productivity than a deeply rooted plant would have.
Vegetables that can grow in 8 inches of soil include cabbage, chard, eggplant, pumpkin, and turnips. Plus, you can grow all of the vegetables listed above for 6 inches.
Can you grow vegetables in 12 inches of soil?
While 12 inches is shallower than most backyard gardeners prefer to plant in, it is possible to grow your vegetables in just 12 inches of soil. If all you have available to garden in is porch or window plant pots, these might be good options.
Vegetables that can grow in 12 inches of soil include broccoli, cabbage, Chinese cabbage, kale, onions, potatoes, and spinach. Plus, you can grow all of the vegetables listed above for 6 inches and 8 inches.