Planting Method
Ridging: The plants are grown on ridges or mounds. The ridges are especially beneficial in areas liable to flooding and also ease harvesting. Cuttings are laid 30 cm apart on the ridge with the basal end planted in the soil. Holes of suitable size are made, the vines placed in the holes and soil pressed down firmly around the cutting. Cuttings are planted vertically with 3 - 4 buds (nodes) under the soil surface
Flatbed: Some farmers grow sweet potatoes on flat beds in sandy soil with good results.
Spacing
Sweet potato can be regarded as a field crop rather than a home garden vegetable. This is because it is a runner and takes large spaces.
For the home garden (where space is limited) a row or two could be enough. Place stem cuttings 25-35 cm apart (or length of spade blade) within the row. Generally mounds or ridges of 1 m apart are used. But it can be 90-150 cm apart for field production or 80-90cm for home gardens, and about 30-40 cm high.
Planting Time
Areas with light mild frost: Beginning of November to mid December. Areas with heavy frost: Mid November to beginning of December. Frost-free areas: August to March. In cooler areas September to February. Winter rainfall areas: mid November to beginning of December; November is optimal.
Fertilization
Soil samples should be taken few months before planting in order to rectify soil fertility problems. Different fertilizer products can be applied depending on the soil type. Ammonium sulphate will tend to reduce soil pH while LAN will increase soil pH.
General recommendations
Sweet potato is heavy feeder of nitrogen and potassium therefore the ratio of N and K must always be kept high. Approximately 1000 kg/ha (100g/m2) of a fertilizer mixture such as 2:3:4 (30) can be broadcasted directly before planting and must be worked into the soil slightly before making the ridges. For sandy soils the amount can be increased to 1200 kg/ha.
Apply a top dressing of 120-150 kg/ha LAN (12 g per meter of row) or 200 kg/ha (20g/m2) ammonium sulphate at 3 weeks after planting and at 6 weeks after planting if necessary. Sandy soil will require at least two top dressings. Water well after application of fertilizer.
Compost may be used to supplement a part of the chemical fertilizer. However, the compost should be well-matured (6 months). Or else be worked into the soil some time before planting. 15-20 m3 (4 big hands/m2) can be broadcast and incorporated before planting.
Irrigation
Sweet potato is moderately drought tolerant. It means that the plant will still produce a yield under fairly dry conditions. But lack of water will reduce the yield. Water stress during the first few weeks after planting and the period of storage root formation (30-60 days after planting) will cause low yields. As a general guide, sweet potato requires between 450 and 600 mm of water well distributed throughout the growing season.