Have I told you yet about my love affair with sweet potatoes? Have I explained how they are the ideal plant for a front yard vegetable garden; the perfect combination of beauty and ease and taste? Have I mentioned their attractive foliage and their purple flowers?
Oh. Yeah. I did. Looks like I already covered that pretty well in my post about the sweet potato harvest last fall.
Ok, then. We won’t cover that again. Instead, let’s talk about growing sweet potatoes.
You may not know this, but sweet potatoes and potato potatoes are nothing alike. Sure, they are both tasty treats that grow underground. But, that’s where the similarities end. Sweet potatoes are related to morning glories, which explains their cheerful purple flowers and their rambling vines. But, those trusty Irish spuds? They belong to the tomato family, and are cousins to peppers, tomatillos and eggplants — the nightshades. Sweet potatoes like the heat. They need the heat. Potato potatoes? Well, they thrived in Ireland (until they didn’t). Heat is not something they really appreciate. Cool and moist suits them just fine. This is why we plant our spuds in the early spring, and wait until the real heat sets in to introduce the sweets to the garden.
Here, in northern Virginia (USDA Zone 7a), we can plant our regular potatoes in March. But, the sweet potatoes should wait until early to mid June. No risk of frost, and plenty of promise for heat. Just what those tropical vines desire. And, while we can harvest early potatoes by mid-June, we won’t be digging up the sweet potatoes for months. If you want a nice full harvest, you really need to give your sweets 100 days (or more) of serious growing time.
If we don’t plant the sweets until June, why am I writing about them in April? Well, because, if we want sweet potato seedlings in June, we need to start our sweet potato slips in April. Or, thereabouts.
Note: You can skip this whole thing, and just order sweet potato slips from a quality nursery or seed company. But, what’s the fun in that? Well. Ok. Actually, there is one BIG advantage to purchased slips: quality seed companies offer a much greater selection of sweet potato varieties than your average grocery store.
To make new sweet potatoes, we start with an old sweet potato. An organic sweet potato (the non-organic sweet potatoes may be treated with sprout-suppressing chemicals). Ideally, you’ll start with a locally-grown organic sweet potato, because then you’ll know that variety will thrive in your region. But, don’t sweat this step too much. A sweet potato from the grocery store should also work just fine. Just, really, buy an organic one.
Don’t think organic makes a difference here? Watch this girl’s video about her sweet potato project. You may change your mind.
Ok. So, you’ve got your organic sweet potato. Great. Now, we’re going to cut it up. Just slice it in half, across the middle.
Next, place each section of sweet potato into a container with water. Plenty of people use toothpicks to suspend their sweet potato halves in a glass of water, but I think it’s easier to just set the whole thing into a casserole dish. Use enough water so that about an inch or two of the potato is submerged.
Set the container near a window, and you’re done. Over the next few weeks, the sweet potatoes will send out little baby plants. Your only responsibility during this time is to keep that water level fairly constant. The sweet potatoes will take care of everything else.
After four to six weeks, you should have a nice growth of little baby sweet potato plants. These will become your slips.
With any luck, some of your sweet potato sprouts will already have roots. Excellent. These little plants-to-be are ready for planting. Others won’t have any roots at all. No worries, those laggards will catch up real fast.
Remove the sprouts by snapping them off at the point where they emerge from the sweet potato tuber. Congratulations! You have your first sweet potato slip!
If the roots are well-formed, you can go right ahead and plant your slip. Some folks recommend planting slips directly into the garden, but I like giving the seedlings a headstart with some rich potting soil (not seed-starting mix). This allows you to keep the roots evenly moist while the plants establish, and gives the seedlings a nice burst of nutrients (I plant into a blend of leaf humus, compost and dirt). Also, if it’s still cold outside, this step is a necessity. Sweet potatoes hate to shiver.
So, that’s it for the little over-achieving sprouts. But, what about the other ones? The rootless ones?
Well, that’s easy too.
Same process. Just slip those sprouts right off the tuber. Then, instead of planting them in soil and compost and leaf humus, you’re going to soak those slips in a cup of water. Just a few inches of water is all you need. Within a few days, you should have roots. Then, you can plant those slips into pots as well.
Once you’ve got all your sweet potato slips in their pots, all you need to do is keep them happily watered until it’s warm enough for them to move outdoors. I like to keep mine in a big styrofoam box. Easy to water. Easy to transport outside for some sunlight during the day. And, easy to bring inside again before the evening chill.
No styros? Well, anything that holds water should do fine. A casserole dish. A plastic storage tub. A big pot. It’s just easier if it holds water and holds a bunch of seedlings, because you could be doing a daily shuffle from inside to outside to inside again for a while now.
Whatever you keep them in, it’s best to coddle your sweet potato seedlings until two or three weeks after your last frost date. Then, once the nights are reliably above 50°F, you can plant them out into the garden. Most people grow their sweets in the ground. I prefer containers, because it makes the harvest easier. Last year, I tried bushel baskets with great success. This year, I’m building a big potato planter. And, yes, I’ll be doing bushel baskets too. A gardener can never have too many sweet potatoes.
It takes all summer to grow a proper crop of sweet potatoes, but it’s worth it.