Post #G21-002: Sweet potato slips, rewritten: Ditch the glass.

Posted on March 17, 2021

My latest discovery as I plan out my garden is that there are few hot-weather vegetables that I would care eat.  I’m not quite desperate enough to grow eggplant (yet).  But I’m getting there.

I’ve decided to grow some sweet potatoes.  They like the heat, and by reputation, they’re easy to grow.  Except for that weird part about growing slips by suspending a sweet potato in a glass of water.  That’s unappealing.

Turns out, the sweet-potato-in-a-glass-of-water method is more of a kid’s science experiment than a gardening technique.  Real gardeners grow sweet potato slips by placing sweet potatoes in a warm, moist, loose medium, such as soil, potting soil, sand, or sawdust. 

And that’s the point of this post.  I’m going to try to summarize the best available advice on this topic.  See the bullet points at the end for the bottom line.



I’m planning to grow a lot of vegetables solely as cool-weather crops this year.  In particular, I’ll be growing cucumbers and summer squash as an early crop only, with plans to tear them out in early July.  This is to avoid having to deal with the pests that plagued those crops last summer.

Now I have to figure out what to replace those crops with, in the heat of the summer.

The problem is, there aren’t a lot of crops that thrive in (say) August in Virginia, that I would care to grow and eat.  Okra, peppers, and maybe some beans.  I may even break down and grow eggplant this year.  But there’s only so much of those things that you can grow and eat.

Which brings me to sweet potatoes.  I’ve never grown sweet potatoes before, but I hear it’s pretty easy to do.  They like the heat, and I happen to have about a dozen sweet potatoes that got a bit moldy sitting around.  Since I’m not going to eat them, this seems like a zero-risk way to try growing sweet potatoes.

Sweet potato slips

You can grow sweet potatoes by planting whole sweet potatoes in the ground, but that’s inefficient.  Near as I can tell, almost everyone grows “slips”, that is, sweet potato sprouts that sprout from eyes on the sweet potato.  And then plants the slips.  Thus getting numerous vines from each sweet potato.

You will see a variety of instructions for growing sweet potato slips by suspending a sweet potato over a cup of water.  To tell you the truth, I thought this was the only way to do it.  And that’s one of the reasons I’ve never tried growing sweet potatoes.  That looks like a fussy, labor-intensive, hit-or-miss process.  (Plus, I doubt that would work with sweet potatoes that have some surface mold on them already.)

Instead, the method that I found most appealing was to grow the slips in dirt.  I first saw this approach in a YouTube video from the Deep South Homestead.  The gist of which is that you put the sweet potatoes in warm dirt, cover with about 6″ of sawdust, and let them sprout.  About seven minutes into this, he pretty much dismisses the whole approach of starting sweet potato slips in water.

Another YouTube gardener I trust for good advice is The Rusted Garden. That’s a Maryland gardener who seems to offer sound advice for gardening in Zone 7.  He did a quick side-by-side comparison of methods:  Sprouting in potting soil, versus sprouting in a glass of water.  If you’re not convinced, just look at the opening of the video.  As you can immediately see, sprouting these in soil was a lot quicker.

And, in fact, if you look for it, you soon realize that all of the advice for professional growers suggests starting sweet potato slips in some loose, solid medium.  Here’s the Mississippi State Extension Service, and they say to sprout them in moist sand or sawdust.  The additional detail they provide is the temperature.   They want you to keep the sweet potatoes quite warm — 80 degrees FarenheitFlorida state extension service agrees, more-or-less, both as to method and high temperature.

Georgia state extension service adds some more useful advice (.pdf).  First, approximate 55 lbs of sweet potatoes to produce enough slips for an acre.  (That seems like remarkably few sweet potatoes.  And in fact, it’s a typo, because because Kentucky’s extension service (.pdf) says 550 lbs of sweet potatoes will provide enough slips for an acre, which they make out to be about 13000 slips).  Assuming I have that all straight now, that a pound and a quarter of sweet potatoes should provide enough slips for 100 square feet of garden.  That’s about four or five medium sweet potatoes.  And about 30 slips, at the planting rates recommended in that reference.  Which also gibes with a rule-of-thumb of a dozen slips per sweet potato.

The upshot is that if you sprout these in a solid medium, you only need to do a handful for a typical backyard garden.

Virginia Cooperative Extension Service out of Virginia Tech does not itself address sweet potatoes, except to say that in this area, they may be planted well after the last frost date, and may be planted as late as the first week of July (per this document, .pdf).   They do, however, provide access to a manual for raising vegetables in the Southeast, where sweet potatoes are addressed extensively.

This manual also provides extensive information on pests, and, as it turns out, cucumber beetles like sweet potatoes.  So I wonder if the cucumber beetle problem I had last year will just transfer over if I plant sweet potatoes this year.

Several sources suggest “pre-sprouting” sweet potatoes by holding them in a warm, 90%-humidity environment for a month before starting slip production.  That speeds up the process, but I don’t have any way to do that.

Different sources offer different recommendations for transplanting the slips.  It looks like the preponderance of sources for commercial growers tell you to leave the roots behind, and just transplant the stem, stripped down to just a leaf or two.  That’s to avoid transferring diseases across garden beds.  Others, such as The Rusted Garden, root the cuttings in water before transplanting them, roots and all.


  • For every 100 square feet of garden, you need to sprout four or five medium sweet potatoes to provide the slips.
  • A typically commercial planting rate works out to be 30 slips per 100 square feet.
  • All sources agree that sprouting them in some warm, moist solid medium is the way to go.  Ditch the glass.
  • In Virginia, slips may be planted well after last frost, up to about the first week of July.
  • Of the pest problems that these may have, the one that caught my eye is cucumber beetles, as I had a lot of those around last year.

And so, I now have a few sweet potatoes sitting in a plastic shoebox of potting soil, on a warming mat.  If nothing else, it’s a lot less effort than trying to grow them in water.