Don't hold it against them just because they belong to the morning glory family... yes that's right, the same family as that climbing vine with the gorgeous blue flowers, which is such a weed!! So the family name is Convolvulaceae and the fancy Latin is Ipomoea batatas. (Don't ask me to pronounce it!)
So this means that Kumara love to grow in a long warm season. I have grown these and on the whole they have been quite an easy crop to grow, they just need some space, and for quite some time too!!
Prepare the soil with any ferts, compost prior to planting and don't feed them again otherwise they will put all their energy into growing tops and not tubers. Lime the soil at this point as well. Don't dig deep, just aerate the soil. Ideally they like to grow in a light soil with a pan or hard layer underneath so when they hit the hard spot they will start to grow tubers.
Make a mound around 20 cm high and plant them like a J in the soil, get the slip mostly all in the soil and just leave the outer leaves showing and keep them moist until they take off. Those brand new slips can run out of water if the soil surface suddenly turns dry. I have always planted mine at 40 to 50 cm spacing along a mound.
One growers secret for growing kumara is to not cut the runners back but rather keep lifting them so that the tops don't root into the ground. This will mean that they will put their energy into growing the tubers. My old boss knew a thing or two when we planted them through left over polythene mulch.... the poly would have stopped the tops rooting down and kept the soil much warmer as it attracts the heat.
When the plants start to die down and the tops are going yellowish, approximately 4 to 5 months then this is the time to harvest. Take care lifting these beauties out of the soil as you want them as undamaged as you can and then dry them off in the sun for a few days and they should store for up to 5 months in a dark airy cupboard.
These are available in bundles of 25 for $9.99 per bundle. Follow the links above to purchase online.