We really enjoy sweet potatoes. It is great for baby food, baked for dinner, as hash browns or fries, or even for some desserts. Naturally, I wished to grow them, being a gardener.
Some have said they are not worth growing outside the South, but others here in the Pacific Northwest (and even some in northern Canada!) have had success growing this nutritious root vegetable with a few tips. I decided to give it a shot and will share the tips I have heard for any fellow northerners wishing to grow sweet potatoes.
What many grocery stores call yams are actually not true yams. They are in reality, colored sweet potatoes. Yams originate from Africa and are not even sweet and hardly grown in the USA. Chances are what you think of as yams are actually sweet potatoes.
Sweet potatoes like it hot. Even over 100 degrees hot. Around here it only gets this hot in July or August. I grew some last year that did fine in these months but did not produce much. What most northerners do is put down clear vapor barrier plastic. I used 4 mil construction plastic. Make sure this is UV treated. I made the mistake of assuming mine was when it was not and it became brittle and split apart into thousands of pieces from the sun.
Stretch out the plastic and bury the edges or place boards on top of them to keep the heat in and the plastic from blowing away.
Several weeks before planting, you can give your sweet potatoes a boost by placing them next to your wood stove or in a humid heated closet at around 90 degrees. You can then remove the 4-6 inch sprouts (slips) and plant these directly. Otherwise you can purchase slips or plant the entire sweet potato. Smaller sweet potatoes grow more slips, surprisingly.
Every foot, cut a slit in your plastic sheeting about a foot long with a box knife. Place your slip or whole sweet potato in each slit, burying it in the dirt. I use wood chips as mulch, so I placed mine on top of the dirt but within the wood chips. Some will grow in the wood chips and others may still grow in the dirt.
Some recommend watering with warm water to keep the soil all the hotter. Since I use wood chip mulch, I do not even water mine much. Thick mulch keeps much moisture in the soil. The mulch and heat of the soil should keep most weeds from growing also.
As the slips grow into vines, make sure they grow up through your slit in the plastic. This should happen naturally, but if some are stuck underneath, go ahead and pull them through.
The vines should quit growing as soon as temperatures no longer reach 90 degrees or so. Frosts will kill them back completely. Try to avoid letting them get down to 40-50 degrees so they do not harden up for the winter.
Sweet potatoes are perennials (surviving over mild winters — hardiness zone 7+). They can grow as far down as 5 feet deep and 80+ pounds if left enough years. So if you leave at least one small one in the ground in mild climates, they should come back next year.
Upon harvesting, I found the sweet potatoes brittle and easily broken like carrots. Digging around them with my hands seemed to be the most successful method. If you planted whole tubers like I did, rather than slips, the tubers may have rotted or dried up. You can discard these largest tubers. It is obvious which are old versus new by the color and texture of the skin.
I was happy with the harvest I got. I filled a five gallon bucket with the new tubers. I should also have plenty small tubers to plant next year.
Once harvested with a fork or your hands, they develop their sweetness through curing. Leave them in 90+ degree humid temperatures for a week or so (or again, next to your wood stove or heater with a wet towel over them and a draped trash bag on top to hold in moisture). Then store them a few weeks in a cool room or root cellar. The sugars should develop so that their sweet with this curing process. Try one and see how it is. Maybe save the smaller ones for next year. The largest are best eaten as they do not grow as many slips.
Make sure not to store in an air tight container. Years ago we stored some in a plastic bag and they quickly rotted. Sweet potatoes let off gases and thus must breathe. Also do not let them get too cold (anything less than around 40 degrees) or they will harden up and be less edible.
We often just throw a sweet potato in our microwave for around 5+ minutes and eat straight or with butter and seasoning. There are many other ways to prepare these tasty tubers.