Growing Potatoes
The potato is a low-growing, leafy, green, herbaceous plant in the Solanaceae plant family. It is generally a warm-season root crop. Tubers can be stored in a cool, dark place for several months.
There are many different varieties available, hundreds in fact, and these also vary depending on where you live. Early, mid and late season varieties are also worth considering, in order to prolong the harvest period. Potatoes also vary in colour according to the variety, with white, red, brown, gold and even blue skinned varieties readily available. Varieties also differ in how you can cook them – some are good all-purpose varieties, others are more suited to salads or mashing or chipping. Choose varieties that suit your needs and your preferences, or the preferences of your market but also take note of which ones are said to have better storage capabilities. That way, you can have potatoes from your garden all year round or extend the life of the crop if you are growing on a commercial basis.
In warmer parts of the world you're best growing varieties which mature quickly because potatoes don't tolerate warm soils. In warm temperate regions consider planting crops in late summer through to early autumn so that they last into winter. In milder temperate regions, try planting late maturing potatoes in spring for a winter crop. Nowadays, you'll also encounter many potatoes which can be grown at any time of year in temperate regions. But if you plant late, you can harvest early. New potatoes are potatoes which are harvested when still young and small.
Growing Conditions
- Potatoes are fairly adaptable but dislike extreme heat or frost.
- Potatoes grow fairly well in most soils, as long as it is moist and drainage is good.
- pH should ideally be ideally around 5.5 - 6.0. Prepare the soil with applications of a phosphorus fertiliser (e.g. rock phosphate, sugar waste, shrimp waste, bone meal). Avoid the use of manures, unless they are used at least 4-5 months prior to planting.
- Sprouts usually appear 3-4 weeks after planting of the tubers ('seed' potatoes). Gradually hill soil around the plants: to form furrows between the rows. The hilling provides support to the plants, and protects the new potato tubers from being exposed to the sun.
- Crop rotation is important.
- Mulching with a mixture of grass clippings and comfrey leaves is reported to deter scab (a fungal disease) developing.
- Potatoes respond well to regular watering if soil is well drained.
- Commercial crops are grown on the broad-acre on mounds formed by tractor-drawn implements.
Notes:
Yields are directly affected by day-length (short days promote tuber formation) and temperature. In most cases (other than potato cultivars specifically bred for warmer regions) the optimum temperature for best tuber production is 15 - 18°C: maximum temperature for optimum production is 25°C, minimum temperature is 7°C.
Plant seed potatoes in early spring in temperate zones and late winter in warmer regions; in tropical regions they are grown during the coolest months of the year. In sub-tropical highland areas potatoes may be grown year-round due to high solar radiation and also milder temperatures.
Nutrient Requirements
Most soils are fine for potatoes but if you have a heavy clay soil you may be best creating a raised mound and growing your potatoes in it rather than trying to persevere with clay. Clay is not only hard to dig, but also for the tubers to grow in. Dig a trench and plant seed potatoes with eyes facing upwards at a depth of about 12 to 15cm. Place about 5 to 6cm of soil on top of the potato and, as it grows, continue to mound up the soil around it. Don't allow the tubers to get exposed to sunlight because they'll turn green and become poisonous. Once the potato has flowered you can stop mounding up the soil. When the tops start to die off it's time to harvest.
- Potatoes have a heavy nutrient requirement. They require higher levels of phosphorus, otherwise similar nutrition to tomatoes. NPK 7:1:9.
- pH must be 5.0 to 6.0.
- Soil should not become too warm, though foliage can withstand heat.
- Soil must be deep (30cm or deeper).
- Good drainage and aeration are essential. Grow on hilled mounds.
Planting
- Normally grown on the broad-acre on mounds formed up by tractor drawn implements.
- Propagated from tubers for most of year, but best planted late winter.
- Buy certified tubers which are free of virus disease.
- Cut large tubers into pieces with at least one eye on each piece. Plant sprouting pieces of tuber direct. Disease is reduced if whole tubers (not cut) are planted). If planting large seed tubers they may be cut, despite the disease risk.
- Place the tubers 30-40 cm apart, 15 cm deep and in furrows 75 cm apart.
- Plant progressive crops: early crops, second-early and the main crop, you can also try for a late season crop. Planting in this way can extend the harvest over many months.
- Tubers must not be exposed to light. The green tissue which results is toxic.
- Soil may be pushed up to cover any exposed tubers (using a plough). And again as plants grow.
Care
It takes about 4 weeks for the potato to emerge from the ground and produce a leafy canopy – during this time there is a danger of weed infestation. Weeds compete with the crop and will influence future yields.
Weeding
- Remove all weeds as they appear.
- Weeds that are growing between the growing plants after earthing up may be removed mechanically or by usually spot control with herbicides.
Hilling
Ridge or hill up crops once 15 – 20cm tall: the initial mounding the crop with soil from between the rows keeps the plants in an upright position keeping foliage off the soil. Hilling also prevents infestations of some insect pests e.g. the potato tuber moth, helps to prevent weeds and improves yields. Hilling-up of the ridges is repeated 3 times during the growing season usually at 2- 3 weeks intervals and this later hilling prevents greening of potatoes.
Adding fertiliser during growth stage
Fertiliser requirements are reasonably high especially on irrigated land or where soil nutrition is weak. On fertile soils extra fertiliser may not be needed to anywhere near the same extent.
Add well-decomposed organic manures to soil before planting to maintain soil structure and nutrient balance. Avoid fresh manures as this may cause potato scab.
Don’t over-use lime – potatoes grow best in acid soils, potato scab is prevalent on neutral to alkaline soils.
Test your soil for nutrient availability before applying extra fertiliser – over fertilised soils can create lots of top growth at the expense of tubers. Extra nutrients need to be estimated correctly according to the cultivars you are growing, the ultimate use of the crop and yield expectations.
Keep soils moist especially during warm dry conditions – potatoes are more susceptible to scab in dry warm soils – the most critical period being between 2 – 5 weeks are tuber formation.
Watering
Potatoes have shallow roots and therefore need to be grown in moist soils a crop that is grown for 120 days will need about 500 – 700mm of water. Low soil moisture affects crop yields especially in the mid to late growing period.
Irrigation periods are usually timed at around 2 day intervals depending on the prevailing weather conditions.
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