Math: Sweet Potato Economics
Sweet Potato Slips activity:
Paper and pencil
In about mid-April, you can place some sweet potatoes
in jars of water to get some sprouts to grow. Then you can plant those sprouts
outside, and come harvest time, you will have tons of sweet potatoes to eat,
enjoy, sell and share!
But even if you didn't start sweet potato slips this
year, you can do a little bit of math to see how a do-it-yourself garden
project like this can save you - or make you - a sweeeet amount of money!
- Let's say a
medium sweet potato weighs about one pound, and costs $1.29 at a store or
Farmers Market. You buy three. How much have you spent? (See answers,
- That is your
"initial investment" in this project. Now cut each one in half. Surely you
have six plain jars or clear glasses around your house that the sweet
potato halves can fit inside. Surely you have some toothpicks, too - and
water coming out of your faucet? Therefore, your only "start-up cost" is
what you spent on the three sweet potatoes.
- Follow the
activity plan, above, to set up the sweet potatoes to sprout slips for
you. Now wait 2-3 weeks!
- Sprout time! The
typical sweet potato will produce several slips. After about a month, you
should have all the sprouts you're going to get. Let's say that each sweet
potato half produced 6 sprouts for you. You started with 3 sweet potatoes
and cut them in half, so you have 6 halves. If each half produced 6
sprouts, how many sprouts do you have altogether? (That's 6 x 6 - see
- Let the sprouts
grow 'til they are 6" long. Then gently twist them off the sweet potato.
Lay them sideways in a bowl of water so that the bottoms of the stems are
in the water. It's best to put this bowl of water where it won't get
knocked over, out of direct sun, but a place where there's plenty of
indirect light, and it's pretty warm. A kitchen windowsill or a sunny
indoor back porch are perfect.
- This should
"root" the slips so that each will have a "rootball" that's a couple of
inches long. Once you have those rootballs, you can plant the sweet potato
slips outside in the warm garden soil - mid- to late May is best, since
the soil needs to be pretty warm, day and night, to make the sweet
- Let's figure out
how many sweet potatoes your slips are likely to produce! In #4, did you
come up with 36 sprouts? That's the answer. Each sprout, when rooted and
grown in the garden, becomes a sweet potato plant. Now, did you know that
each sweet potato plant produces about 10 new sweet potatoes, if you
fertilize the plants about twice a month and make sure they have enough
water and so forth? So if you planted 36 sprouts, and each one produced 10
new sweet potatoes, how many sweet potatoes have you grown? (36 x 10 =
- Last, but
certainly not least, let's check the dollar value of your work. Did you
come up with 360 sweet potatoes for #5? That's the answer. Now imagine
that you could sell them at a grocery store or Farmers Market for full
retail price. (You wouldn't charge that much because you're a KIDS group
and don't have to figure on any harvest, transportation, storage or
retailing costs, but just imagine that you could get full retail price.)
So what's the dollar value? Remember that a medium sweet potato costs
about $1.29? If you produced 360 sweet potatoes, and could sell them each
for $1.29, how much money have you just made? (see answer below) All you
have to do is subtract your initial investment - your answer in #1 - and
what you spent on fertilizer and water over the summer months, which
usually is not much.
WOW! How do you like these economics? Pretty
ANSWERS: #1 -- $3.87 . . . #4 - 36
slips . . . #7 - 360 slips . . .
#8 -- $464.40 - $3.87 initial
investment - $20 fertilizer and water = $440.53 NET