How to Plant Sweet Potato Slips: Timing, Depth and Spacing

What a slip is and what a good one looks like

A slip is a rooted shoot pulled from a sprouting sweet potato, not a tuber and not a seed. It arrives looking like a wilted cutting with a few leaves and a scruffy bunch of white roots, and that is normal. Slips travel badly and almost always look half dead on arrival; they recover once their roots are in damp soil.

A good slip has a stem eight to twelve inches (20 to 30 cm) long, five or more leaf nodes, and a stem thick enough to feel firm between your fingers. Reject anything with a blackened base, because black rot enters at the cut and will follow the plant into the ground. If the slips will sit for a day or two before you can plant, stand the bases in an inch of water in a jar out of direct sun.

1. Count the nodes You need at least three nodes to bury and two leafy nodes above ground. Storage roots form from buried nodes, so a short slip means fewer roots.
2. Check the cut end The base should be pale and firm. Any black or soft tissue means rot, and it will not grow away. Discard it rather than planting it and hoping.
3. Rehydrate before planting Stand the bases in shallow water for a few hours to overnight. The leaves will lift and the slip will take hold far faster once planted.

Plant by soil temperature, and be patient

Sweet potato is a tropical crop and it does nothing at all in cold ground. Below 60F (15C) the roots simply refuse to grow, and a slip planted into cold soil sits there yellowing for three weeks and never catches up with one planted a fortnight later into warm ground. Wait until all frost risk has passed and the soil at four inches (10 cm) deep is over 65F (18C).

In practice that is two to four weeks after your last frost date, which feels uncomfortably late compared with everything else in the garden. Under black plastic you can plant at the earlier end of that window. The crop needs roughly 100 to 120 frost-free days from planting to a worthwhile harvest, so count backwards from your first autumn frost to check you have room.

Lay the slip sideways so more nodes are buried

Every buried node can become a storage root, so the way you set the slip in the ground directly controls how many potatoes you dig. Planting it upright like a bedding plant buries one or two nodes. Laying the lower half of the stem horizontally, three inches (8 cm) down along the top of the ridge, buries four or five and roughly doubles the number of roots.

Point the buried section along the ridge, not across it, and bring the leafy tip up at an angle so two or three leaves stand clear of the soil. Firm the soil over the stem with your palm and water it in immediately. The slip will wilt flat within an hour of planting; that is expected and it stands back up in two to four days.

1. Open a shallow sloping trench With a trowel or your hand, draw a trench three inches (8 cm) deep and six inches (15 cm) long along the top of the ridge, sloping up at the far end.
2. Lay the stem in horizontally Strip any leaves that would end up buried, lay the lower half of the stem flat in the trench, and angle the leafy tip up out of the soil.
3. Cover and firm Backfill so all bare nodes are covered and press down along the length of the stem. Loose soil around the stem dries out and the nodes never root.
4. Water in and shade for two days Soak the base thoroughly. In hot, bright weather lay a handful of straw or an upturned pot over the tip for the first couple of days.

Do not panic when the slips collapse the afternoon you plant them. Judge them on day four. Anything still flat and gray by then has failed and should be replaced while there is still season left.

Spacing decides root size, not root count

Total yield per square foot barely changes across a wide range of spacings, but the size of individual roots changes a great deal. Plant twelve inches (30 cm) apart and you get many medium roots, good for baking whole. Plant eighteen inches (45 cm) apart and you get fewer, much larger roots, some of them too big to be convenient in the kitchen.

Fifteen inches (38 cm) between slips along the ridge, with three feet (90 cm) between ridge centers, suits most gardens. The wide row spacing is not wasted: the vines fill it completely by midsummer and smother almost every weed, which is the main reason this crop takes so little work once it is established.

The first fortnight after planting

Water every second day for the first two weeks unless it rains, keeping the top three inches damp so the buried nodes can root. After that the plant needs remarkably little attention. New leaves at the growing tip are the sign it has taken; the original leaves often yellow and drop, and that is not a problem.

This is the moment to write things down. Note the planting date, the number of slips and their spacing, and the position of each ridge. Sweet potato gives you no visible signal about what is happening underground for four months, so the record you make now is the only way to interpret what you dig up in autumn and to make a better decision next spring.

1. Water every other day for two weeks Enough to keep the top three inches (8 cm) damp. Once new growth appears at the tip you can drop to watering only in dry spells.
2. Replace failures within ten days Any slip still flat and gray on day four is dead. Replace it promptly; a slip planted ten days late still crops, one planted a month late does not.
3. Record the date and layout Note the planting date, spacing and ridge positions. Next year you can compare digging dates and spacings against what you actually harvested.