How much garden space do I need for 12 sweet potato plants?

Planting sweet potato:

The best soil for sweet potatoes is sandy, but they can grow in all soils. If you have heavy soil plant sweet potatoes on mounds or ridges.

Raising the beds improves the drainage (very important) and gives the tubers a nice deep soil to develop in. (Otherwise you may end up with small, bent and forked sweet potatoes.)

The soil should have a good supply of nutrients, for example from digging in mature compost. Do not use fresh manures or any fertilizers high in nitrogen (like pelleted chicken manure). You'd just end up with lots of leaves and no tubers.

Growing sweet potato:

Growing sweet potatoes requires some space, so plant them where they can spread. Space your cuttings or slips about a foot apart in a row, and leave three to four feet between rows. (If you plant in rows, that is...)

Mulch thickly between plants and even between the beds to initially keep the weeds down. Once the sweet potatoes grow they will choke all weeds down themselves.

For planting time the general recommendation is to plant a patch in spring. (May in the northern hemisphere, November in the southern). In a cool climate you may indeed have to get by with a single planting. Sweet potatoes do need four to six months of reasonably warm weather to mature.

But in the tropics one big spring planting does not make sense, unless you are a commercial grower.

Sweet potatoes don't keep well after harvest, so the best way is to plant a few cuttings every week or two. Just one row of one meter length, with three cuttings. They will take about 16 to 18 weeks to mature in warm weather, longer in cooler weather.

That way you can grow sweet potatoes all year round, and you don't find yourself with a big pile of them all at once.

For a regular potato cut it into quarters and plant 2" deep with at least one "eye" on the potato seed.