Growers of sweet potatoes plant slips, not seed, or tubers. A slip is a sprout, with stem and leaves, which grows from a sweet potato tuber. Snap off the slip, root it for a few days, then plant it in the garden.
How to obtain slips:
1) Buy them locally. In my area of NYS very few garden centers carry slips. Call before driving.
2) Buy them through a catalog or on-line. Make sure to buy sweet potatoes suitable for your area. For northern areas the variety should produce a crop in 95-105 days. The minimum order is sometimes 12 slips, more often 24 slips, at roughly $1 each, plus shipping. This can get expensive, particularly if you only want a small sweet potato patch. (I plant 8 slips.) The growers of sweet potato slips take care to ship at the best planting time for the buyer’s area. For my area, they ship just before Memorial Day for planting at the end of May. The slips languish in the Post Office over the long weekend, and arrive more dead than alive. Two years ago, I ordered 25 slips. The grower shipped 30, of which 19 survived.
3) Grow your own. This is fun and fairly easy even if you don’t have ideal conditions. You must plan ahead however because the process takes months.
Growing Sweet Potato Slips at Home
Over the last two springs, I’ve tried 3 ways of growing slips. Each works but one is better than the others.
1) Slips can be grown by keeping the sweet potato in water. I placed this potato into the glass jar 3/1/2008. A week later I spotted its first root and by 3/17 it had several 1/4″ roots. Around 4/12 the first slip slowed as a tiny bump near the top. This picture was taken 5/3, the day I broke off the two longest slips to root them.
The disadvantages of keeping the potato in water were low productivity of slips (there are only 4), and by June the sweet potato rotted below the water line.
2) In 2009 I started the process by rooting the sweet potatoes in water. After 2 weeks, when there were several 1/4″ roots, I planted some of the sweet potatoes in potting soil. I used a clementine crate, laid the sweet potatoes on their sides and covered them completely with their top side 1/2″ below the top of the soil. This method wasn’t very productive: I got only 2-3 slips per potato. One advantage was the potatoes didn’t rot. In June I removed them from their box, scrubbed, cooked, and ate them.
3) The method that worked best was rooting the sweet potato tubers in water for 2 weeks, then planting them waist deep. My best potato provided 8-9 sprouts, even under my less than ideal conditions.
Growing Slips: Step by Step
1) Obtain ‘mother’ sweet potatoes. The mother potatoes should be locally grown to insure they will produce a crop in your area. Select the best potatoes available: avoid cracks, bruises, and black skin. A good place to find locally grown sweet potatoes is a farmer’s market in the fall. Sweet potatoes store well laid on a shelf in an unheated basement and you can save the best for growing slips. Do as I say, not as I do – the potatoes in the picture were the best I had.
2) Root the potatoes by placing them in water up to their middle for two weeks. The most difficult part is figuring out which end goes up. That should be the end attached to the main root while growing. Often both ends taper, but at one end the point ends abruptly in a small, flat area while the other end continues to taper to a thread like root which is the bottom. If the sweet potatoes were cured in very high humidity there may already be a slip or a small bump showing where a slip will grow: place that end up.
If all else fails, submerge the entire potato then check to see which end develops roots.
See this post for more information about distinguishing the top from the bottom.
3) Keep the sweet potatoes in a warm, humid area while rooting and growing slips. Although 80 degrees is ideal, slips will grow at lower temperatures, it just takes a lot longer. My house temperature ranges between 65 and 68 degrees.
4) When the sweet potatoes have several 1/4″ roots, remove them from the water and plant each in a pot just a bit bigger than the potato. I use commercial potting mix.
5a) When the young slips have 3-4 full-sized leaves remove them from the sweet potato to root. To remove a slip, grasp it at its base where it emerges from the potato and twist.
5b) Alternately, you can let the slips grow on the potato until quite long, 12″ or more. Then a couple of weeks before you want to plant in the garden, remove each long slip by its base and cut it into sections of 2-3 leaves each. If you’ve started the process very early, use this method, because the removed slips need only 1-2 weeks to root. After that, they become pot-bound.
6) Remove the bottom-most leaves from the slips. For faster rooting dip the bottom 1/2″ in rooting powder. Insert slips in deep, slender pots filled with potting mix. My favorite pots are deep plastic 6-packs that originally held flowering annuals.
Keep the pot inside in the shade for 3-4 days, until roots develop, then gradually move it into the sun, increasing its time in the sun each day.
7) Plant rooted slips in the garden after the last frost, when the soil is quite warm. Near the Hudson River in Poughkeepsie, NY, I plant during the last week of May and early June.
8) After the big slips are removed the remaining slips will grow rapidly. The next batch will be ready in 5-7 days.
9) Eat the mother sweet potato when you are finished growing slips. Remove it from the pot, brush away the soil, scrub, and prepare as usual.