How to know best time to plant sweet potatoes in Missouri?

Planting sweet potato is not as easy as it seems.

Here’s why:

So if you plant them outside too early in the spring they will die. And if you plant them too late, your sweet potato won’t produce a harvest before the first frost arrives in the fall.

Today, I’m going to teach you the ideal time to plant sweet potato in Missouri:

As you may have already guessed, you need to pay very close attention to your local weather in the spring. Specifically, you are going to need to watch when the last frost occurs.

In general, when there hasn’t been a frost for two weeks, you are SAFE to plant your sweet potato outside in Missouri!

For your reference, I have created this table for average frost dates for most major cities in Missouri. If your city is not listed below you can find its Last & First Frost Dates HERE.

Missouri Last & First Frost Dates

Unfortunately, Mother Nature plays cruel tricks on us every year.

It should be noted that the above dates are just averages.

There are years when the last frost comes MUCH later. Sometimes, the last frost happens much earlier and you can get your sweet potato planted outside in Missouri much quicker.

Like I said before, you need to be very diligent in checking your local weather.

So what happens if a frost comes AFTER you plant your sweet potato?

When you know a frost is coming you need to take action.

Also, make sure not to plant your sweet potato in your garden too late.

Depending on the type of sweet potato, it takes roughly 40-50 days to grow sweet potato from seed indoors and then transplant them to your garden.

For a specific date that you should start sweet potato seeds indoors you should:

Not only this, but I recommend again paying close attention to your local weather report.

It should also be noted that the best technique for bringing your sweet potato plants outside is to introduce them (in their pots) outside for an hour. And then increase the amount of time they spend outside each day by an hour until they have been outside for 8 hours.

This will “hardened” your sweet potato plant, increasing its chances of fighting off diseases, insects, droughts, and wet conditions.

If you want to learn WHEN to plant ANY Vegetable in Missouri, head over to HERE and just type in the vegetable you want to grow.

Heat – Sweet potatoes need hot weather to grow.  The slips are best planted when nights are 60 degrees and higher, often after May 1.

Drainage – Sweet potatoes need to be planted on a mound or in a container so that during wet spells the potatoes growing underground don’t rot.

Sunshine – Plant these veggies where they can get sunshine for at least 8 hours a day.

When planting in ground, develop rows about 3′ apart, mounded up to 8-12″ high.  Place the plants (or slips) 10-18″ apart on top of the row by using a stick or narrow trowel to insert the plant.  Water the slip in with a solution of Fertilome Blooming and Rooting fertilizer and firm up the soil when done.  Mulch or straw can be used to hold soil in place and retain moisture.

Container growing is easy, too, especially when it’s time to harvest. However, the size and number of sweet potatoes produced will be in direct proportion to the container size.  Also, that container is dependent upon you for moisture!

Georgia Jet – deep orange inside, red-purple outside

Beauregard – orange inside, red-orange outside

Centennial – carrot color inside

Murasaki – white inside, purple outside

White Yams – white inside and out

Sweet potatoes slips can be started two different ways: by shallowly planting a sweet potato in potting soil or to cut a sweet potato in half and place the cut end into a jar of water.  Use toothpicks inserted into the potato to support it so that only the cut end is always in water. In both cases, as green growth emerges from the potato and reaches 4-6″ in length, pull these “slips” off the potato and place directly in the ground or grow in water for a few days.

In Missouri, sweet potatoes can be planted in late April (Southern Missouri) through mid to late-May (central and northern Missouri) when soil temperatures are warm and all danger of frost has passed.

Ben Sharda is KCCG’s Executive Director and he has led KCCG for more than 30 years. His practical approach to gardening has played a key role in KCCG’s success. This month, Ben offers tips on fertilizing your plants.

I probably get more harvesting questions about sweet potatoes than any other crop. And, that makes sense because with other crops like tomatoes or lettuce, you can see what you are harvesting and decide when to harvest based on appearance. With sweet potatoes, it is harder to know when to harvest because they are INVISIBLE (well, almost – because they are growing underground).

Sweet potato plants are planted in May and then grow all summer and the vines grow and spread out. Hopefully you have mulched them and kept the weeds out and watered when it was needed. If you have a lot of leafy vines that look healthy, that is usually a good sign that you will have a good sweet potato harvest.

September is the month to harvest sweet potatoes. August is too early and October is too late (usually too cold and rainy). During August, sweet potatoes are getting larger underground. By the second week in September, night time temperatures are starting to cool down which stops the sweet potatoes from getting any larger. I recommend digging one sweet potato plant, early in September, as a test to see what they look like. If they seem small you can leave them a little longer to hope that they get a little larger.

To dig a sweet potato plant, follow the vine back to the stalk that goes in the ground. Then, cut off most of the vine (to make it easier to see where you are digging) and leave the main stalk at 10-12 inches to give you a “handle”. Then clear away the cut vine and measure out about 12” and use a digging fork (sometimes called a potato fork) and dig down and underneath the clump of potatoes. Then pull back on the fork and lift up to raise up the clump of sweet potatoes. Then separate the potatoes and place them in a shallow cardboard box or plastic crate.

A few things to remember:

• Use first any sweet potatoes that may have been accidentally speared during the digging process. They won’t keep very long.

• Store your sweet potatoes in a warm dry place in your house. (65 degrees or warmer)

• Try to dig you sweet potatoes when the ground is dry. (so they will not be covered with mud!)

• Do not wash the sweet potatoes until you are ready to cook them. (gently loosen the dirt off them)

Sweet potatoes are nutritious, starchy root vegetables. Sweet potato plants are in the same family as morning glories (Convolvulaceae), and are only distantly related to potatoes. Since they are not in the nightshade family (Solanaceae) with potatoes, sweet potatoes are a dietary alternative for people who are sensitive to nightshades.

Sweet potato plants are heat-loving, low-maintenance garden vegetables. They have a vining growth habit and the plants establish quickly. They enjoy full sun (at least 6-8 hours during the growing season) and thrive in loose, well-drained, nutrient-rich soils – although they will tolerate almost any planting site.

Select and prepare the planting site for the benefit of your sweet potato plants so that, come harvest, you get a bountiful crop! Here's what we recommend.

Plant. Space planting holes at least 12 inches apart and space planting rows about 36 inches apart. This allows space for vigorous vines to grow and avoids light or nutrient competition, while also giving you room to move easily through your planting site to mulch, water, and eventually harvest.

Mulch. Sweet potato plants don't like water-logged soil, but dry soil is just as stressful. Be sure to keep the planting area watered as needed (you shouldn't need to water if there is rain in the near forecast). Apply a few inches of mulch to help retain moisture while also discouraging the development of problematic weeds.

Most varieties of sweet potato will mature within 3-5 months, so, if your location is known for having short growing seasons, be sure to choose varieties with an appropriate maturity time.

Sweet Potato Varieties at Stark Bro's

Harvest-sized sweet potatoes may be found several inches below the soil surface. Carefully remove the soil from around the plant's roots and examine the tuber size. If they are a couple inches across or larger, they are ready to be harvested. You can selectively remove the sizable sweet potatoes and re-cover the plant's roots to allow continued development of smaller ones. Be careful not to bruise, scrape, or puncture the skin of the sweet potatoes as this can cause quality issues like rotting, especially in storage. Remove any excess dirt from your harvest.

Sweet potatoes are an excellent vegetable crop to include in the field or garden in Missouri. They are high in fiber and in vitamins A and C and low in fat, making them a very nutritious vegetable. Sweet potatoes are often called yams in the United States, but a true yam is a starchy, edible root botanically unrelated to the sweet potato. Locally grown sweet potatoes are becoming a popular produce item at farmers' markets across Missouri.

Sweet potatoes are propagated vegetatively rather than by seeds. That is, seed stock is used to produce slips, or transplants. Slips can be purchased from several suppliers in the Midwest and the southeastern United States, but for larger plantings it may be more economical to purchase seed potatoes and produce your own slips. Always purchase certified or virus-indexed seedstock for slip production. Certified seed will produce the most slips per bushel and have fewer disease problems, and the sweet potatoes will be more uniform in size, shape and quality. The seed potatoes should be bedded when the soil temperature reaches 60 degrees Fahrenheit. One bushel of seed potatoes will produce about 1,000 slips from one cutting or 2,000 from three cuttings. About 20 bushels of seed potatoes will be required to produce enough transplants for one acre.

Presprouting the seed by holding the seed potatoes at 75 to 85 degrees Fahrenheit and 90 percent relative humidity for two to three weeks will increase the number of slips per seed. To minimize rotting in the plant bed, the seed potatoes can be dipped in a fungicide. The plant bed should be located in a well-drained site. Place the potatoes in a single layer 2 to 4 feet wide, and cover the beds with about 2 inches of soil. Do not bury the seed potatoes too deep. Top-dress the bed with a general-purpose, granular fertilizer (for example, 10-10-10), and cover the bed with clear or black plastic. Punch small holes in the plastic to aerate the soil and prevent carbon dioxide and temperature buildup. When the potatoes sprout about an inch, remove the plastic. Row covers can be used to protect the plants in the event of a frost. Sweet potato slips can also be produced using a hotbed or propagation beds within a heated greenhouse.

Slips can be cut from the plant bed when they reach a height of 12 to15 inches (Figure 1). Cut hardy slips 1 inch above the soil line, and plant in the field or garden. Do not pull the slips because this will often transmit root diseases. About three cuttings can be made from the plant bed. Destroy the plant beds after you have harvested all the slips.

Figure 1Sweet potato slips for transplanting can be purchased from some seed suppliers, or they can be be produced from certified seed potatoes.

Sweet potatoes (Ipomoea batatas Lam.) are warm-season vegetables in the morninglory family. Sweet potatoes thrive in warm weather and are very sensitive to frost.

'Beauregard', 'Hernandez', 'Jewel' and 'Centennial' are suitable varieties for Missouri (Table 1). 'Beauregard' is a high-yielding, disease-resistant variety with a light red skin and a dark, orange flesh. 'Hernandez' and 'Jewel' are copper to brown skinned with dark, orange flesh and perform best in sandy soils. If you desire a white-fleshed sweet potato, consider growing varieties such as 'Nancy Hall', 'White Delite' or 'White Hayman'.

Table 1Suggested sweet potato varieties for Missouri.

In Missouri, sweet potatoes can be planted in late April (Southern Missouri) through mid to late-May (central and northern Missouri) when soil temperatures are warm and all danger of frost has passed. Plants (slips) are planted three to four nodes deep (3 to 4 inches deep), 9 to 18 inches between plants in rows 36 to 48 inches apart. A node is a bump or swelling on the slip where a leaf was attached. Orientation of the slips is not crucial because slips can be planted upside down and still will produce sweet potatoes. Make sure that there is good soil moisture and use starter fertilizer solution or water after transplanting. The wider the spacing between plants, the faster the sweet potatoes grow or "size up". Sweet potatoes should be planted on ridges or raised beds (6 to 9 inches high). Raised beds aid in root development and improve soil drainage and aeration. Sweet potatoes do not tolerate waterlogged soils. Avoid planting in fields that were previously in sod because this could result in significant white grub and wireworm problems in the sweet potato planting. Soils that are high in organic matter may not produce quality sweet potatoes. Sweet potatoes should be rotated with other vegetable or agronomic crops to prevent pest buildup.

Sweet potatoes can be planted on plastic mulch (for example, black). The mulch will maintain a friable (loose) soil, conserve moisture, suppress weeds and increase soil temperatures. Sweet potatoes grown on plastic mulch will mature faster. Organic mulches such as straw, paper or wood chips can be used to suppress weeds and reduce loss of soil moisture.

Sweet potatoes tolerate acidic soils and the soil pH can be 5.0 to 6.5 for successful growth. Before planting, phosphorus and potassium should be applied based on a soil test. Nitrogen should be applied three weeks after transplanting (11 ounces per 1,000 square feet). An additional side-dress application of 11 to 12 ounces per 1,000 square feet of nitrogen can be applied when the vines begin "running" off the beds. Avoid applying too much nitrogen to sweet potatoes. Excessive nitrogen results in extensive vine growth, but few sweet potatoes.

Sweet potatoes are tolerant of drought, but for maximum yield and quality, 1 inch of water should be applied to the crop each week. Few disease pathogens attack sweet potatoes in Missouri, but insects such as wireworms and white grubs can be a problem.

Weeds should be controlled until the sweet potato vines cover the bed, which occurs about six weeks after transplanting. This can be achieved though cultivation, mulching or herbicides.

Most sweet potato varieties are ready to harvest 95 to 120 days after transplanting. Generally the leaves turn slightly yellow when the sweet potatoes are ready to harvest. Pulling or cutting the vines two to three days before digging will toughen the skins and help reduce skinning of the sweet potatoes. A hill of sweet potatoes will yield about 2 pounds of marketable sweet potatoes and an average yield per acre of 400 bushels (50 pounds) is attainable. Sweet potatoes should be harvested before the first frost in the fall. Frost will kill the vines but should not damage the sweet potatoes.

Sweet potatoes can be harvested by various methods. For large-scale production, a riding harvester is used to dig one or two rows at once. For smaller scale growers, a chain-driven, one-row harvester is commonly used. A turn plow will also be effective in dislodging the sweet potatoes in light-textured soils. If the sweet potatoes are in heavy soils that are dry at harvest, a light irrigation of the soil before digging will reduce skinning. Sweet potatoes should be handled as little as possible to prevent bruising and skinning. When handling sweet potatoes, workers should use cotton gloves to reduce skinning. Sweet potatoes are often packaged in slatted, bushel crates holding 50 pounds or larger 1,000-pound wooden or plastic bulk bins. The sweet potatoes can be graded at harvest or anytime before marketing. Do not wash the sweet potatoes until they are ready to be marketed.