Growing vegetables is one of life’s joys, and when you start to see your vegetable patch come to life, it can be an incredible feeling. However, you need to know what soil conditions your chosen vegetables need in order to thrive, so choosing the right vegetables that match the depth of your soil is imperative. If your soil isn’t deep enough, many vegetables with long roots won’t be able to thrive.
The vegetables that need deep soil to grow include sweet potatoes, tomatoes, and carrots. Winter squash and cucumber also need fairly deep soil so they can spread their roots sufficiently. If your soil isn’t deep enough for these vegetables, they’ll likely become stunted in growth.
In this article, I’ll go through all the vegetables that need deep soil to grow. I’ll include some specifics about each one, including the soil pH level they need in order to thrive. I’ll also go through what happens when your soil is too deep or not deep enough and the consequences of crowding vegetable seedlings.
1. Sweet Potatoes
Sweet potatoes grown at home can come in one of three colors: white, orange, or purple. However, they can occasionally be yellow, too! Growing sweet potatoes can be extremely rewarding, and they’re not particularly high maintenance vegetables, either, so they’re an excellent choice for a beginner gardener. However, they do need one thing in order to grow big and juicy: deep soil.
They’ll need just under 20 inches (50 centimeters) of loosened soil in order for the roots to delve deep into the ground. Mixing up a few layers of the topsoil with organic materials (such as compost) will also help your sweet potatoes become lovely and sweet.
It generally takes up to 170 days for sweet potatoes to become ready for harvest. That might seem like a long time, but it’s good to remember that these veggies are fairly large, bulbous creatures that need around three months of warm, sunny weather in order to grow to their full size.
If the weather isn’t warm enough, or you live in an area that doesn’t allow your vegetables to get full sun, it’s usually a good idea to grow them indoors or in a regulated environment such as a greenhouse, just to make sure they’re as warm and toasty as possible.
One thing sweet potatoes dislike is being overwatered. Overwatering will drown those lengthy roots once the soil becomes waterlogged, and they won’t be able to grow to their full potential size.
Therefore, try to keep them in deep, tilled soil that has a relatively neutral pH level. Around 6.5 is the perfect pH level for your sweet potatoes, and they’ll always love a good dose of organic materials to help them along.
2. Tomatoes
Tomatoes are another example of a vegetable that needs deep soil – but they don’t usually need as much depth as sweet potatoes. While sweet potatoes need about 20 inches (50 cm) of free soil, tomatoes typically do well in soil that’s around 15 inches (38 cm) on average.
Tomatoes grow just as well in pots as they do in the ground outdoors, so as long as your plant pot is big enough to house those roots, you’re good to go. However, since tomatoes generally prefer sunny, humid environments, they might be best placed in a sunny conservatory for the ideal results.
Here’s a little tip to get those tomatoes to grow big and juicy: when you’ve got your soil in the pot before planting, dig a little hole where you’ll be planting the seedlings. Place a few snippets of banana peel around the area and gently cover it up. This will help your tomatoes grow quickly in the early stages of their life, and the added organic matter and nutrients will help them thrive in the long term.
Since tomatoes can grow to pretty hefty heights (sometimes to a whopping 1.8 meters or 70 inches), it’s helpful to grow them in deep soil. This can help the plant hold on to something while they grow, and this way, it won’t topple over. If you’re growing a variety that can get this tall, it might be a good idea to plant them outside, as they’ll have more space to grow out there and won’t be impeded by the edges of a pot.
Additionally, tomatoes are slightly alkaline-loving vegetables with a preference for a soil pH of around 6.5. Therefore, consider adding a little bit of lime to your soil if you find it’s too acidic for your tomatoes.
If you would like to explore the steps towards improving your soil for tomatoes, check out my article: How To Improve Soil for Tomatoes (DIY Guide)
3. Carrots
Carrots most definitely need deep soil since the part of the carrot we actually consume is the part that grows underground. This is precisely why it’s called a root vegetable!
Carrots are typically relatively straightforward to take care of and can even withstand a few hefty frosts. They’re an excellent option for a beginner gardener – you just need to make sure you’re taking good care of its soil.
The best place for carrots is soil that has been tilled. Tilled soil is typically slightly loose to allow the root formations to spread outwards. The ideal soil depth for these bright veggies is around 10-12 inches (25.4-30.48 cm).
Since carrots need a lot of space, it’s usually a good idea to give them lots of space when planting. Try not to plant your carrots too close together since the roots tend to be lone wolves and don’t like the company of other carrots. The soil needs to be able to accommodate the carrot’s potential size – otherwise, you’ll end up with small, shriveled carrots that aren’t as big and beautiful as you had hoped.
The best soil pH for carrots is relatively neutral – anything up to 7.0 is typically considered ideal. Additionally, your soil shouldn’t be clay-based, and if it is, you should add some coarse sand or at least some organic materials to boost its nutrient levels. Carrots will do well with compost, so try to till compost into the first few inches of the soil to accommodate for this.
4. Winter Squash
Winter squash is a family of vegetables that includes several kinds (including pumpkins and butternut squash), and they’re typically the larger section of the vegetable kingdom. They can grow to quite a fair size and may quickly become the most prominent part of your garden.
However, winter squash are relatively picky vegetables. Not being as easy to please as carrots, they need lots of time to grow to their full size, and they’ll invariably need more frequent watering and more sun. Additionally, if they experience a frost, they’ll quickly shrivel and hide – so if you’re planting them in cool temperatures, make sure you protect their bed with a garden tarp or cover to keep them warm.
Winter squash don’t just need deep soil; they also need width. Since their roots grow outwards as well as down, each one should be at least 3 feet (91 centimeters) apart. Warm soil is ideal for these sensitive veggies, and the soil should be around a foot deep (30 centimeters). If the soil is warm enough, your squash seedlings shouldn’t take too much time to sprout, and you’ll begin seeing proper growth within just a couple of weeks.
Additionally, winter squash tends to favor sandy soils with a slight acidity – around 5.5 pH is generally considered ideal. While these vegetables take quite a while to grow before they can be harvested, they’re definitely worth the wait to be able to use fresh squash in your fall recipes!
5. Cucumber
Cucumbers are incredibly versatile, so it’s no wonder that people like to grow them in their gardens. Cucumber roots can often grow fairly deep, so you’ll need to make sure you have lots of space for them to spread. 48 inches (around 120 cm) is considered the norm with cucumbers. However, not all cucumber roots will grow in the same way.
The biggest difference between the humble cucumber and all the other vegetables on this list is the way in which their roots form. Cucumbers usually germinate initially with only one root – this is called a taproot. This is the very first sign of germination, and the taproot will continue to grow while the rest of the root system starts to form.
Once growth has begun and the cucumber begins to get bigger, most of its roots stay small, usually at the top of the soil near the sunlight. However, the taproot chooses to stay down in the depths of the ground and is responsible for keeping the cucumber upright and taking essential nutrients from deep in the subsoil.
Since cucumbers have lots of tiny roots at the surface of the soil, you’ll also need to ensure that you leave enough room between cucumbers when planting. This will guarantee that the smallest roots at the top can spread while the taproot has enough room at the bottom to maintain the cucumber’s equilibrium.
Additionally, the best temperatures for cucumbers are warmer and wet – springtime is usually considered the best time for planting. Slightly alkaline soils are a must with these veggies, and you should always keep them properly watered so that the taproot doesn’t dry out. That moisture is essential for the root to be able to take in the nutrients from the depths of the soil.
What Happens if You Plant a Deep Rooting Vegetable in Shallow Soil?
If you’ve already planted your vegetables and since discovered they needed deeper soil than you could offer them, you can still salvage the situation. Transplanting your vegetables to a bigger container with deeper soil is a good way to ensure those roots will grow properly.
If you plant a deep rooting vegetable in shallow soil, you’ll find that the roots won’t be able to grow at all. A lot of the time, these roots are in the habit of collecting moisture from the subsoil, and if they can’t do that, they may well dry up – especially if the weather is scorching hot.
Additionally, if your deep rooting vegetable grows very tall, you’ll likely find it will topple over once it has grown. This is because the soil is too shallow to support the roots properly.
Another issue with planting vegetables in shallow soil is that the roots situated in the topsoil will be more susceptible to insect infestations. They’re closer to the surface of the soil, so they’re more accessible to hungry insects and other pests, such as beetles.
What Happens if You Plant Vegetables Too Deep in the Soil?
On the other end of the spectrum, it certainly is possible to plant vegetables too deep in the soil. For first-time gardeners, it might be more challenging to figure out exactly where your seedings should be placed and how deep. However, before planting any vegetables, it’s crucial to know how deep to plant your seedlings, as planting them too deep can result in no plant growth.
Newly-planted seeds typically need sunshine and moisture to germinate properly. They should have access to adequate moisture, and they should also have access to oxygen. The oxygen comes in handy when the roots begin to sprout since the roots need oxygen to “breathe.” They take in oxygen, use it as an energy source, and then secrete carbon dioxide. If the soil has good aeration, this process should be a breeze for your new vegetable seeds.
One big sign that you’ve planted your vegetable seeds too deep in the soil is if they haven’t germinated after a few weeks. How long it takes to sprout will typically depend on the type of vegetable, the care you’re giving it, and the time of year you’ve planted it. However, if it’s been more than 4 weeks and you still aren’t seeing any little tufts poking up through the soil, you may indeed have planted them too deep.
Unfortunately, if you live in a colder region with short summers, this means you’ve lost precious time in the one season where you can plant your veggies. There’s really no fixing this, and you’ll just have to wait until the next appropriate season to try again. This is why it’s especially important to know at what depth to plant each of your vegetable seeds before doing so.
What Happens if You Crowd Vegetable Seeds?
Crowding vegetable seeds can have a similar impact on growth as planting them at the incorrect depth. Growth will be stunted, and your veggies will inevitably take much longer to grow.
If you don’t give your vegetables enough space to grow, it’s very likely that they won’t be able to grow to their full size. This is especially the case for vegetables such as carrots and parsnips since their roots are very big and need extra space to form deep within the soil.
Additionally, if you crowd your plants too much, you may end up with unwanted diseases in your soil. There won’t be enough nutrients per plant, and they’ll be fighting over organic materials in the subsoil. Therefore, researching your specific vegetable and seeing how much room it needs to thrive is essential. Otherwise, you could end up with small, sad vegetables or even no vegetables at all.
Which Vegetables Have the Shortest Roots?
Unlike vegetables that need deeper soil, some vegetables only need an inch or two to survive. This is a useful skill since it means their delicate roots can take in essential nutrients right from the top of the soil. Additionally, vegetables with small roots tend to be a bit smaller, so they don’t have to worry about toppling over when growth hits a new level.
The one big difference between shallow-rooted veggies and their deep rooted counterparts is the amount of moisture they need. Since vegetables with shallow roots are more exposed to the hot, dry heat of the sun, it means they lose moisture much faster than those with deep roots. Losing their moisture content quicker often means the topsoil dries out, too.
Over time, if you’re not giving shallow-rooted vegetables enough moisture, they won’t be able to grow properly. This is often why people say that these veggies are the most high maintenance!
Examples of vegetables with the shortest roots include bok choy, kale, and green onions. Green onions are some of the simplest vegetables to plant and care for, and their roots are so tiny and delicate that they hardly need any space at all. If you’ve run out of space in your garden, you can just plant them in a little pot on your kitchen windowsill!
I’ve also written a complete guide about the soil requirements for growing onions. I’ll also share a few tips to help you get better yield: How Deep Does Soil Need to Be for Onions?
Kale is one of those plants that will grow to wonderful heights if you allow it. However, if you give it a small space, it can thrive just as well – it just won’t be as big. The great thing about kale (particularly for beginner gardeners) is that the roots won’t die if you don’t give it lots of space – it will just be smaller when the time for harvesting comes around.
