Is this your first year planting sweet potatoes, or did you have trouble growing them last year? If so, then you are not the only one.
Lots of gardeners wonder what kind of soil is best for growing sweet potatoes. Using the right soil for sweet potatoes will yield a much better harvest in the fall.
So, what soil is best for sweet potatoes? Sweet potatoes grow best in warm, loose soil that drains well (for example, sandy loam soil). The ideal soil for sweet potatoes has a pH of 5.5 to 6.5. Add some organic material to your soil (such as compost or aged manure), which will help sweet potatoes grow better.
If your soil does not exactly fit the profile described above, don’t worry – there are ways to improve it. Let’s get into what type of soil you need to grow sweet potatoes and how to prepare your soil for growing them.
What Soil is Best for Sweet Potatoes?
According to the Texas A&M University Extension, sweet potatoes grow best in soil that is fine and well-draining, such as sandy loam. A pH of 5.5 to 6.5 is ideal, but sweet potatoes will tolerate a pH between 5.0 and 7.5.
Sweet potatoes are a warm weather crop, so they need warm soil and prefer full sun. They can tolerate frost if the soil temperature is over 55 degrees Fahrenheit (13 degrees Celsius).
If the soil in your garden sticks together easily and you can mold it into shapes (like clay), then you have clay soil. Clay soil has very fine particles, and this type of soil retains water because it drains slowly.
The particles in clay are very tightly packed, making it a dense soil. Sweet potato tubers form underground, so clay soil will make it harder for them to grow.
Mix some compost or aged manure into clay soil to add organic material. This will make the soil looser, which will make it drain faster. Compost will also add some nutrients to the soil.
If your garden soil is loam (not clay), but denser than you want, then add some sand to the soil to loosen it up. Remember: do not add sand to clay soil. You will get very hard soil that will be tough to work with!
Sweet potatoes, potatoes, carrots and other crops (whose roots or tubers grow underground) grow much better in loose soil. Loose soil allows these crops to grow freely without running into dense clumps of soil.
If your garden soil is very sandy, then it will drain fast – possibly too fast. This can lead to water shortages for any plants you try to grow, no matter how much you water.
If your soil is light, breaks apart easily, and dries out very quickly, then you likely have sandy soil.
Regardless of which kind of soil you have in your garden, you can improve the texture by sifting the soil. A soil sifter will remove debris (such as roots, rocks, and soil clumps).
You can build a soil sifter out of wood, nails, and rabbit wire with small holes. Or, you can buy a soil sifter online if you don’t want to build one.
Soil pH and Nutrients
The ideal soil pH for growing sweet potatoes is 5.5 to 6.5 (somewhat acidic to slightly acidic). If you don’t know the pH of your soil, do a soil test to find out.
You can find home soil test kits online or at a garden supply center. You also have the option to send a sample of your soil to a local agricultural extension service for testing. If you want to learn more about these options for getting a soil test, I’ve written an article all about it here.
A soil test will reveal the soil pH, and it will also indicate how much of each nutrient is in your soil. The most important nutrients for plant growth are nitrogen, phosphorus, and potassium (also known as NPK, or the “big three”).
A soil test will tell you if your soil is lacking one or more of these critical “big three” nutrients. In that case, you should add a supplement to provide the necessary nutrients for your soil as you prepare to plant your sweet potatoes.
How to Prepare Your Soil for Sweet Potatoes
Don’t panic if your garden soil is not perfect for growing sweet potatoes. There are ways to improve the soil – it just takes some preparation.
Sift to Remove Debris
As mentioned earlier, sifting your soil will remove debris, such as rocks, sticks, and roots. With less debris, there is more space for soil, which holds water, air, and nutrients for your plant’s roots.
Sifting your soil also makes it looser. Sweet potatoes will have an easier time growing in loose soil, since they can grow freely without running into obstructions like rocks or roots.
Adding compost to your garden will improve any type of soil – not just clay. When you add compost to your garden, you are adding organic material (for instance, decomposed grass clippings and leaves from your yard).
The organic material in compost builds the structure of your soil. At the same time, compost contains nutrients that are essential for plant growth.
Compost also encourages beneficial soil organisms to come to your garden (for example, bacteria and earthworms). Beneficial soil organisms add air to the soil (which is necessary for plants to breathe!). They also help to convert the nutrients in leaves, grass, and other debris into a form that plants can use to grow.
Adding compost to your garden is one of the best ways to keep the soil healthy. The best thing about compost is that you can make it for free, using kitchen scraps and yard waste that you already have lying around. If you want to learn more about how to make compost, then check out my article here.
Use Crop Rotation and Cover Crops (Green Manure)
When you practice crop rotation, it means you are planting different crops in a given location each year. For instance, in one part of your garden, you could plant tomatoes in year 1, peas in year 2, broccoli in year 3, and so on.
Crop rotation prevents plant diseases from spreading in your garden. It also helps to maintain nutrients in the soil, since different crops take (or replace) certain nutrients in the soil.
Planting cover crops (or green manure) is another way to improve the soil in your garden. A cover crop is a plant that you grow in the garden to replace nutrients that other plants have used up and depleted.
For instance, you could plant alfalfa (Lucerne) in your garden at the end of the growing season. Alfalfa has deep roots, which can pull nutrients from deep in the soil where shallow roots cannot reach.
Eventually, you will till the alfalfa into the soil, where it will decompose. After the alfalfa breaks down, its nutrients would become available to whatever plant you decide to grow next year.
Crop rotation, cover crops, and compost will replace some nutrients in your garden soil. However, there are times when extra nutrients are needed, especially if you are growing “heavy feeder” crops that use up lots of nutrients.
In these cases, it is a good idea to use supplements that can add the necessary nutrients back to your soil. As mentioned above, a soil test will let you know which nutrients are lacking in your soil.
A balanced NPK fertilizer, such as 10-10-10, will add some of the “big three” nutrients (nitrogen, phosphorus, and potassium) to your soil.
There are other options for adding specific nutrients to your soil. For example, some high-nitrogen fertilizers include:
- Feather meal
- Blood meal
- Fish meal
- Manure (chicken manure generally contains the most nitrogen!)
Just be careful about using too much nitrogen on your sweet potato plants. Excessive nitrogen encourages “green” growth (leaves and vines) without doing much for the tubers (the part of the sweet potato plant that you eat!)
Manure that is not decomposed (known as fresh or “hot” manure) will contain too much nitrogen, and can burn your plants if you apply it to them directly. Wait for the manure to decompose before using it in your garden!
Some high-phosphorus fertilizers include:
- Bone meal
- Burned cucumber skins
Some high-potassium fertilizers include:
- Burned cucumber skins
- Sulfate of potash magnesia
- Wood ash
Whichever supplement you choose, always follow the instructions on the package to avoid burning your plants by over fertilizing.
Sweet potatoes are a warm weather crop, and they prefer warm soil temperatures (the hotter the better for them!) Before planting your sweet potatoes, wait until the soil is at least 65 degrees Fahrenheit (18 degrees Celsius).
Waiting until the soil warms up enough can be a problem if you live in an area with a short growing season (for example, if you live in the northern U.S.). The reason is that most varieties of sweet potatoes take at least 100 days (over 3 months) to reach maturity.
If you want to get your sweet potatoes started sooner, you will need to warm up the soil. One way to do this is to cover the soil with black plastic mulch.
When the sun hits the black plastic, it will absorb the energy and store it as heat in the air and soil under the plastic. This method will work even better if you use mounds for planting your sweet potatoes (highly recommended).
Form Soil Mounds for Planting
Before planting sweet potatoes, dig (or pile up the soil) to form beds 8 inches (20 centimeters) high and 12 inches (30 centimeters) wide. These mounds of soil will help the soil to drain better, and to warm up faster in the spring.
Leave 12 to 18 inches (30 to 45 centimeters) between sweet potato plants. If planting multiple rows, leave the rows 3 to 4 feet apart to allow space for watering, fertilizing, weeding, and harvesting.
Is Chicken Manure Good for Sweet Potatoes?
Fresh chicken manure may be too “hot” for growing sweet potatoes, since it has high nitrogen content and can burn your plants. If you do decide to use chicken manure, let it age and decompose first.
Here are some guidelines to follow if you use chicken manure (or any other manure) in your garden:
- Let the manure age 3 to 12 months, so that it has a chance to break down completely. To help it decompose quickly, use a pitchfork to turn the pile to aerate it. Also, add water to the manure if it dries out.
- Manure that has aged and decomposed enough will look like soil. You should not see any straw, wood shavings, sawdust, or animal bedding in aged manure.
- Combine manure with soil & compost before adding it to your garden. This will decrease the concentration of nitrogen and salt in the manure.
- If you decide to add manure directly to your garden, use a thin layer that is 0.25 to 0.5 inches deep.
How Deep Does Soil Need to be for Sweet Potatoes?
The Old Farmer’s Almanac suggests tilling the soil to a depth of 8 to 10 inches (20 to 25 centimeters) before planting your sweet potatoes. Remember that sweet potato tubers grow underground (the vines grow above ground), so loose soil will let them grow freely.
Alternative Ways of Growing Sweet Potatoes
If you have a small garden with limited space, or if you would like to try a new way of growing, here are some interesting alternative methods for growing sweet potatoes:
- straw bales
- raised beds – I wrote an article about why to use raised beds here.
- grow bags – I wrote an article about why to use grow bags here.
Now you have a better idea of the type of soil to use for growing sweet potatoes. You also have some ways to improve your soil to get a better harvest in the fall.
I hope you found this article helpful – if so, please share it with someone who will find the information useful. Now it’s time to get back to the garden and grow the best sweet potatoes possible!