1) I've never tried growing purple sweet potatoes
2) I've never successfully grown purple sweet potatoes
3) None of these information is absolutely credible, but worth a try
4) In this post, success is based on the growth of the plant till harvest and in possible continuation for consumption purposes. Comments provided are summarized and may be altered based on my 2 cents horti-brain opinions.
5) Information below does not help them taste better because that's a whole new story to tell
Purple sweet potatoes are direct relatives of orange sweet potatoes! The difference in color is explained by the presence of anthocyanins and antioxidants that give the flesh its purple color. What you're eating is actually their tuberous roots. The young leaves and shoots are also consumed as greens.
There are several different varieties/cultivars of purple sweet potatoes such as ‘Purple Passion’, ‘Molokai Purple’, ‘All Purple’, ‘Purple Delight’ and ‘Purple Knight'.
Basic growing conditions of Ipomoea batatas Lam:
Sun Exposure: Full Sun
Soil Type: They prefer well-drained soil. Suggest for you to mix with compost or mulch anyway for nutrients.
Soil pH: 5.5 and 6.5 (Slightly acidic)
Temperature & Humidity: As long as it's summer i think it's okay, most importantly the soil has to be warm enough. Not a problem in SG.
These guys don't need much water and are drought tolerant. Doesn't need much fertilizer either. Basically like a caveman. Also grows like a weed. Normal sweet potatoes and purple sweet potatoes should grow similarly, the only difference i can find is the harvesting period for purple ones take a longer time (about 30 days difference maximum).
What you'll need to grow them:
Sweet potato stem cuttings called "slips" - you know the leaves that grow out from the sweet potatoes that you eat? Ya those. The slips will emerge when you keep both ends consistently moist.
Enough space (they grow quickly) - about 3 feet apart each
Tips to take note:
Water well and frequently for the first several days and be patient. After about two weeks, the plants should be well-rooted and showing hardy growth
For any kind of planting, always do your regular weeding, watering, fertilizing. Don't disturb the roots unnecessarily.
Do not add nitrogen-rich fertilizer to sweet potatoes, as it encourages excessive vine growth at the expense of tuber production. 5-10-10 would be good to induce root growth.
Slightly acidic soil conditions help suppress sweet potato diseases.
Common diseases are: Flea beetles, Sweet potato scurf, White blister, Fungal leaf diseases (Alternaria leaf spot and blight, Botrytis), stem rot
Avoid growing sweet potatoes in areas recently covered with grass, because ground-dwelling grubs and wireworms — often numerous in grass-covered soils — chew holes and grooves into the tubers. (This one is probably for other countries but good to take note)
Once you check that the potatoes are big enough to eat, you can start digging them. Sweet potatoes can be left in the ground as long as the vines are still growing.
Usually they are ready to harvest when the leaves and ends of the vines start to turn yellow
When you dig, just dig carefully and tactfully as they bruise easily.
You need to cure the potatoes before you store them. Meaning to create a second layer of skin. To cure, arrange them in a warm and humid area for 7-10 days.
Once you're done, store them in a dry place. The flavor should improve after a couple of months of storage. oooh..
If all goes well the sweet potatoes should be able to store up till 10 months.
That should be about it! Sounds quite easy to grow. Most of the articles are more into how to cook it cos this crop is so widely grown. There are already so many varieties of purple sweet potatoes in the market, so the taste is an important factor to consider.
I don't go into details on how specifically you should plant it with what material you should use or what brand of soil you should buy because my aim is to teach you what the plant generally needs. There are many alternative ways to do planting with whatever resources you have. Most solutions provided online are homegrown suggestions. It is really up to you to think with the basics of planting.
Check out these NPARKS videos to learn more about soil mixing for edible crops!: