Establishment

Source of Planting Materials

Certified seeds are available from the following KARI Station:-

  • KARI – MTWAPA
  • KARI EMBU
  • KARI KATUMANI
  • KARI KIBWEZI
  • KARI KISII
  • KARI KAKAMEGA

Land Preparation

Sweet potato grows best and produces smooth, well-shaped storage roots in a well-prepared soil. Good land or soil preparation involves removal or incorporation of crop debris and any vegetation that may compete with the sweet potato crop, and deep manual or mechanical cultivation. 

Making ridges or mounds is recommended because of:

  • Higher yields achieved
  • Mechanization possible – during harvesting you can use a ridger
  • Conserve soil moisture
  • Reduces soil erosion
  • Intercropping with other crops possible

Planting on flat bed or fields should be discouraged as it reduces yields

Propagation

Propagated is by use of vines cuttings or storage roots.

Storage roots   

Storage roots are used when there are insufficient stem cuttings available, or when the level of pest and disease infestation is high so that few healthy vines are left.

The sets must be healthy, robust and avoid using the rinds. Cover with little soil 3 cm of soil to avoid rotting. The bed should be covered with straw to help retain moisture. This method is not recommended as the resulting yields are low.

Vines cuttings 

The use of vine cuttings is the recommended practice. This is because:-

  1. They are free soil borne diseases
  2. Use of vines leaves tubers for consumption or selling
  3. Yields are higher
  4. They produces roots with better shape and size

Preparation of planting materials to achieve higher yields

  • Select ‘clean’ planting material that are free of insects, soil, and any symptoms of viruses or fungal diseases.
  • The apical (tip) portion of the vine is better than the middle or basal portions. This portion is less likely to carry sweet potato weevils and fungal pathogens, and has been found to establish faster than other portions.
  • A length of 30 cm is recommended because cuttings of much greater length tend to wasteful of planting material while much shorter cuttings establish more slowly and give much lower yields.
  • The delay between cutting and planting may affect yield depending on the storage conditions for the cuttings. Storing cuttings for one to two days in humid conditions may be beneficial, promoting rooting at the nodes. Longer storage may adversely affect establishment by exhaustion of the cuttings’ energy reserves.
  •  To minimize losses, leaves should be stripped from the lower portion of the cutting, and bundles of cuttings wrapped in a wet cloth or sack and kept in a cool, shady place away from wind. If roots develop during storage, they should be planted carefully to minimize damage to the roots. 
  • In drier areas with only one main rainy season, leave some tubers in the soil over the dry season. When the rain comes the tuber sprout and the new vines are used for planting.
  • If planting material is to be maintained in a multiplication plot before planting of the next crop, plant cuttings at approximately 15 x 20 cm spacing. New growth may be ready for cutting after 45 days.

Planting methods

Sweet potato vine cuttings are planted at an angle with vine ends towards the centre of ridge or mound. 2/3 of the vine cutting is buried in the soil. Depth of planting is 4-6 cm deep

Planting on mounds

  • Make mounds 1M apart (i.e. centre of the mound to the next) each with a base diameter of 30-40cm.
  • Plant 3-4 vines in single stand at equal distance from each other.
Tender sweet potato crop grown on mounds

Tender sweet potato crop grown on mounds

Planting on ridges

Make ridges 1M apart (i.e. centre of the ridge to the next). The base of one ridge to the other is 10-15 cm.

Tender sweet potato crop grown on mounds (image 2)

Tender sweet potato crop grown on ridges

Planting is done either in single or double rows.

  • Single row – Vines are planted at the middle of the ridge at 30cm between plants within the row. This is recommended in drier areas.
  • Double rows – The vines are planted on left and right position of the ridges at 30cm between plants within rows and 50-60 cm between rows. 

Seed rate

  • The recommended no. of cuttings is 27,000 per ha (11,000 per acre)
  • 1 gunny bag of cuttings has approximately 2000 cuttings implying that 5 ½ bags – 6bags are needed for an acre

Time of planting

  • It is done at the onset of short and long rains when there is sufficient moisture to enhance establishment.