Seed Potatoes

Selecting the site

• Potatoes will grow best in a warm sunny position. They will not grow and yield in shade or where they have to compete for light and moisture.
• Shelter from strong winds is also a benefit.
• The size of the potato garden depends on the size of your family and your requirements.

The soil

• Potatoes require a free draining soil rich in organic matter (compost).
• In clay soils, the potato plot should be raised or built up some 15cm above the surrounding soil to ensure good drainage.

The 'seed' potatoes

• Potatoes are grown from tubers known as 'seed potatoes'.  These 'seed potatoes' are grown especially for the purpose in areas that are free of virus diseases. Potato virus diseases can severely reduce yield if the seed potato is infected. 
• Avoid cheap seed potatoes which may not be virus free.
• With potatoes being a major vegetable in our diet, not surprisingly there are numerous varieties with distinct differences in shape, colour, size, yield, time to maturity, taste, and suitability for mashing, boiling, baking or chipping.

Sprouting

• It is a good idea to ensure 'seed potatoes' have a good strong growing shoot emerging from the tuber prior to planting.
• Buy your 'seed potatoes' a few weeks in advance of planting time, and place them in a tray positioned in a warm light position. This will encourage sprouting

Potato Varieties

• When choosing varieties it is a good idea to select varieties according to your needs and to give a spread of maturity with the late ones being stored for the winter.
• Early varieties are those that tolerate the cool early season and are quickest to maturity. They tend to be lower yielding and not good keepers but they are great for that early taste of new potatoes.
  • They can be planted in winter in warm mild districts,and in early September in cold districts, but will need protection from late frosts.
    Popular Early Varieties are
  • Rocket; Swift; Cliffs Kidney; Ilam Hardy
• Main crop varieties cover most, which have an intermediate growing period, maturing in 100-120 days.
• These varieties are best planted in Sept-October.
• Good main crop varieties include
  • Red Rascal, Desiree, (red skinned varieties) which are good all purpose varieties.
  • Agria a pale golden flesh with great taste and good for mashing.
  • Karaka is a new variety bred in NZ and regarded as The Great All Rounder.
• Late varieties tend to be the slower to maturity, high yielding, good for storage varieties.
• Good late crop varieties are
  • Heather- a purple skinned variety (the purple disappears with cooking) which has firm large tubers and a high yield. A general purpose variety which keeps well.
  • Rua-an older type which produces high yields of large oval flat tubers. A good keeper.

Planting

• Potatoes are tubers which form off the underground stem of the plant. (They are stem tubers not root tubers) Hence to produce a good crop it is necessary to ensure there is a significant amount of stem covered with soil.
• The 'seed potatoes' are planted in a hole about 100mm deep, about 400-500mm apart in rows about 800mm apart.

Mounding Up

• When the potatoes have emerged  to 200mm high mound up the soil almost covering the emerged tops.
• When they have grown another 200-300mm, repeat the process.
• This produces a large mounded row in which the new potato tubers will form and grow.

Watering

• Potatoes tolerate reasonably dry conditions, but in very dry weather they may require regular watering.

Feeding

• Prior to planting, apply a dressing of lime. Work this into the soil and leave for a week.
• Then add Tui General Fertiliser or Potato Food and work this into the soil. 

Pests and Diseases

• The major disease of potatoes is late blight. Despite its name, it often occurs early in the season or late, attacking in wet cool conditions. Once infested, it will spread rapidly. Initially black blotches appear on the leaves, which leads to total defoliation.
• Control by spraying at the very first sign of black spots with Yates Greenguard or Bravo.
• Spray thoroughly including the undersides of leaves.

Potato Psyllid - a new pest

• A major newly arrived pest of potatoes is the Potato psyllid.
• The limpet like insect attaches itself to the undersides of leaves.
• As it sucks the sap it also injects a toxin into the plant which inhibits the formation and sizing of the new potato tubers.
• Once this pest is present in your area, regular preventative spraying with Yates Mavrik is required.
• More detail here