We love baked sweet potatoes with real butter! I buy them occasionally when I feel like a treat for dinner. It was only last year that I began to research how to grow them myself and if it would be possible up here in the great white north.
It is, indeed, possible but does take some knowledge and a bit of preparation.
Sweet potatoes are grown from "slips" which are live cuttings from a sweet potato vine. You can buy sweet potato slips from nurseries here, shipped to you at planting time in the spring. You can also grow your own slips now and have them ready to plant out as soon as all danger of frost is past.
Sweet potatoes do not take frost so cuttings must be held indoors, in a cold frame or a greenhouse until time to plant into the garden with the other tender vegetables.
Because they like very warm soil, it is a good idea to prepare a raised row for them. Raised beds warm up faster in the spring. This can be an planter or just a row in your regular garden that has been piled high.
Another way to warm the soil early and almost a must for sweet potatoes is using black plastic mulch. The black mulch will quickly get hot in the spring sun and the soil underneath will be a good temperature for your sweet potato cuttings when they are ready to plant. I have read that the big box hardware stores, like HD and Rona, get shipments of wood covered with large sheets of black plastic which is discarded. I have both of these stores near me and plan to ask them if I can take some of this off their hands.
Black plastic mulch can be used to kill weeds in fields before planting in the spring, as well. Cover the field with it and it will quickly become so hot underneath that it cooks the grass, weeds and weed seeds in the ground, or so I have read. I am hoping to get enough black plastic this spring to try this or, at least, enough to cover my planned sweet potato rows.
To grow your own sweet potato "slips", you need whole sweet potatoes. Stick three toothpicks into the potatoes and suspend them in water. If they are warm enough they will root in the water and grow sprouts. Its these sprouts that you can cut off, root inside and plant in the garden in spring. The sweet potato cuttings or "slips" will quickly root and grow into large vines in no time. It gets big quickly. As the vines grow inside, while you are waiting for spring, you can continue to cut them into smaller pieces and root those, as well.
It is very important to keep the sweet potatoes warm while rooting. I bought two last year from a small grocery that were labelled "Ontario grown". Figuring these would be the short season variety I would like to try, I bought a couple. I suspended them in water for months and they didn't root until it got warm in the house in early summer. I kept them by the back door and they were always cold.
This year I bought three from a large grocery. I don't know if they are northern ones or not but I will try them anyway. I put these in the room above the wood stove and they rooted quickly. All three are well rooted and one has sprouted.
This will be my sweet potato sprout rooting tray. It is just potting soil from the store kept slightly damp at all times. There is one sprout that is big enough to cut and root. Always use a knife when taking any cuttings. If you use clippers or scissors you might crush the bottom so much that it cannot take up water.
This is the one cutting big enough to root. Pick ones that have a couple of leaf nodes on the stem that can be planted under the soil. This is usually where roots grow on cuttings, although not always. Some plants grow roots all along the stem, i.e. brugmansias.
Use the knife to make a hole for the cutting and put it in the hole, filling in with soil and covering the leaf nodes If you have rooting hormone you can use it on these sprout but I don't think it will be necessary. Keep the sprouts very slightly damp until you see new leaf growth.
I am hoping to grow enough sprouts to fill several trays with growing plants before spring.
Sweet potato vines grow across the ground while the sweet potatoes themselves grow under the ground, like regular potatoes. They will cover a large patch quickly in warm soil.
(Sweet potatoes are NOT potatoes. Its a different plant altogether.)
Harvest your sweet potatoes in the fall before frost. Do not wait until frost takes the vines or the sweet potatoes will not be as good.
After harvesting your sweet potatoes you will need to let them cure for several weeks. This is the time the starches are turned to sugars. If you eat them before they have cured, they will not be as sweet. Put them on a screen, out of the sun, in a place where they will not freeze, where they can dry for weeks. They will keep until the following year if stored cool and dry, but not too cold.
You can grow your own sprouts for the following year from some of these potatoes you have grown. You can also take cuttings from the vines to grow indoors until time to cut them up into small pieces for next spring.
This will be the first time I have grown sweet potatoes. I am very excited about it! It will be one of my pet projects for this year.