Sweet Potato Growing

 

At FitzGerald Nurseries we have pioneered the introduction of a wide range of sweet potato varieties to Europe and brought sweet potato production in Europe to a new unprecedented level. We have been working on this crop in collaboration with breeders at Louisiana State University who are breeders of these wonderful varieties we promote. We are now selling sweet potato all across Europe and have developed virus free stock and expertise in the development of this crop in Europe for both gardeners and farm scale availability.

Climate
Sweet potato (Ipomea batatas) is a semi tropical plant that grows best between 20C and 30C requiring a minimum of 120 days of frost free growing conditions. Plant growth is restricted below 10C and plants physically damaged at 1C. Optimum growth occurs between 20C and 30C, and optimum root swelling (they are not tubers) occurs during shortening days. In Northern Europe production is made much more possible through plug production as this method gives fast establishment and a head start to the plant. See section on Sweet Potato from Plugs.
N.B. Gardeners in Ireland and UK are strongly advised that best results are got in greenhouse conditions. While it is possible to get some positive results outdoors in warm sun trap locations this isn’t usually the case.

Soils

Sweet potatoes grow best on well drained sandy loam soils. Heavy soils should be avoided. The pH of the soil is ideally 6 to 7 in saline free soils. Cultivate the soil to provide 20-30 cm of well worked soil. Additional sub soiling will be needed if soil compaction is present to improve drainage and root shape. Ridged beds will aid harvesting.

Planting Material

Sweet potato have been traditionally and are still propagated from cuttings called slips. These slips should be well watered before planting and kept at high humidity’s to encourage rooting. In Northern European Climate this method has its challenges and pre-developed plug or pot production is evolving as a the best alternative.

Sweet Potato Burgundy grown up a tripod in  greenhouse then used as an ornamental feature once sufficient foliage mass achieved.

Slips are planted by hand, with 5 cm to 7 cm of tip exposed. It is best to plant the cuttings half horizontally to the ground rather than vertical. Plug or Pot grown plants can be planted in a similar way but close attention to root spiraling should be observed as once roots start spiraling they will give distorted edible roots, however this is just a visual issue and these roots are perfectly fine for processing or chopping. Row sizes vary depending on climate and potential yield, but in good cropping areas rows should be 100 cm apart and plant 30 cm apart in rows. However in commercial field production if mechanical harvesting is planned bed spaces will vary- ridges 1.2 m apart can be formed, with double rows 30 cm apart and 50 cm apart within the row.

A method well worth trying in greenhouse conditions is to grow Sweet Potato vines in the same way as tomato i.e. up a string. Some fantastic yield results have been achieved in trials using this method. We have also grown them on tripods in containers or ground like beans. These methods maximize light exposure on the leaf surface and also prevent this rampant grower from being too invasive in the greenhouse. If growing like this in a container you will need at least 15 liters of substrate.

When planting in containers 2/3 fill the container and plant, once vine grows clear of the top of container by 10 – 15cm fill remainder of container with potting soil. This encourages maximum yield potential in good greenhouse conditions. In prefect growing conditions yields up to 5 Kg have been achieved on some varieties and typical yield using this method is 3.5 kg per plant assuming good culture maintained.

Irrigation

Sweet potatoes do not like too wet conditions, however at planting it is important the soil is kept moist to ensure good establishment. Yields and quality are seriously affected if the crop is stressed when the harvest roots develop. Over watering though will cause rotting and skin cracking. Sweet potato can crack wide open and become corky in extremes of drying out and wetting dues to surges in growth.

Fertilizer

Sweet potatoes require less fertilizer than other vegetables. Individual recommendations will vary depending on previous cropping and soil analysis before planting. In garden conditions it is important to avoid excessive nitrogen so a balanced feed with low nitrogen fertilizer is desirable. Sweet potato lend themselves to use of non chemical fertilizers but if using organic matter, such as grass clipping or other green waste it is essential it is well composted before working into soil and low in nitrogen.

Weed Control

Sweet potatoes are ideally suited for mechanical weeding assuming no serious perennial weeds are present. During early crop growth, shallow cultivation between rows and hand weeding will control weeds. Once plants cover the ground, the crop tends to smother further weed growth.
Pests and Diseases

The sweet potato crop is relatively free of pest and disease problems. Following a good rotation and hand weeding there should be no need for use of pesticides as many biological control methods are available. However Fusarium is the main cause of root rot, which increases in cold wet soils. It can progress rapidly within the root, so early harvest in warm condition should be encouraged. Planting material selection is the key to controlling virus and disease. Our stock is all from our own elite stock maintenance program, maintained in our own laboratory. All our varieties are maintained virus and bacteria free and mother plants replaced each season. This control of parent material is key to achieving best yield of healthy foots for our customers. Care should be taken against rodents including field mice as in late Autumn they can do extreme damage especially in crops planted through plastic film as they will have perfect shelter and go undetected.
Harvesting

Remove vines before digging the potatoes. The sweet potato is very sensitive to bruising. As such all harvesting and handling must take place with extreme care. In dry sunny conditions sweet potato can be placed on surface of ground in a poly-tunnel similar to how onions are but this should only be done in warm conditions avoiding temps below 10C.

Storing Roots

Do not wash roots intended for storage. Sweet potatoes must be cured by holding them at high temperatures (plus 25C) with a high relative humidity (90%) for upto 2 weeks. This cures the roots by healing the wounds, keeps shrinkage and weight loss at a minimum and improves the culinary qualities of the tuber by converting starches to sugars.

Bon Apetite
Varieties

Evangline
Skin Colour: light rose skin, fades in storage; slightly more red than Beauregard at harvest
Flesh Colour: Intense deep orange Flesh
Specialty: Evangeline produces 40% more Beta carotene than Beauregard
Susceptible/resistance to common diseases:
Soil rot: Intermediate – resistant
Root knot: highly resistant
Fusarium wilt: resistant
Rhizopis soft wilt: resistant
Sclerotial blight: Susceptible
Fusarium root rot: resistant
Bonita
Skin Colour: light tan skin with a pink cast at harvest, fades in storage
Flesh colour: white with a tinge of yellow
Speciality: Unique nutty flavor – ideal for baking. Uniform and good performer.
Susceptible/resistance to common diseases:
Soil rot: Intermediate
Root knot: highly resistant
Fusarium wilt: intermediate – resistant
Rhizopis soft wilt: Susceptible
Fusarium root rot: Susceptible
Murasaki-29
Skin Colour: dark purple skin
Flesh Colour: white flesh
Speciality: Very well suited for boiling and not so sweet than the other varieties, but needs a longer growing time of 120-130 days.
Susceptible/resistance to common diseases:
Soil rot: Intermediate – resistant
Root knot: highly resistant
Fusarium wilt: resistant
Rhizopis soft wilt: highly resistant
Fusarium root rot: resistant
Orleans
Skin Colour: light rose skin
Flesh Colour. Orange flesh with an intensity similar to Beauregard
Speciality: Highly uniform production of storage roots
Susceptible/resistance to common diseases:
Soil rot: Intermediate – resistant
Root knot: susceptible
Fusarium wilt: resistant
Rhizopis soft rot: resistant
Bacterial soft rot: Susceptible (same as Beauregard)
Fusarium root rot: resistant
Burgundy. New!
An outstanding flavoured variety full details soon this variety is wooing anyone who tastes it and is a very special flavour.

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