How to Grow Potatoes

General

Potatoes are important to the self-sufficient gardener and the gourmet gardener. Easy to grow, highly nutritious and there is a variety for every use in the kitchen. Some are for baking, some are for salads, some for French fries. You should try them all!

Latin

Solanum tuberosum
Solanaceae family.

Difficulty

Easy.

Season & Zone

Season: Warm season
Exposure: Full-sun (requires at least 6 hours of sun per day)
Zone: Unknown.

Planting Seeds

Preparing Seed Tubers: Our seed potatoes have been intentionally selected for small seed size and should be planted whole. Larger potatoes can be cut so long as there is at least a few "eyes" per 2.5-3cm diameter piece. "Chitting" is the process of pre-sprouting potatoes in a dark and dry place then moving to a cool light place before planting. Chitting potatoes encourages strong sprouts and can lead to an earlier maturing crop.

It is important to realise that the potato that we eat grows from a runner that forms on the stem of the plant above the seed potato that you set into the soil.

Preparing Soil

A well-drained, loamy soil high in organic matter with a pH on the slightly acidic side (6.0-6.8) would be ideal. If heavy clay or clay loam soils are used, double digging and improving organic matter content by growing cover crops and/or adding composted manure can correct drainage problems. For proper soil fertility in the home garden, dig composted manure into the top 30cm (12") of soil. Use around one wheelbarrow load to 10sq.m of ground. If composted manure is unavailable, homemade compost, a general organic fertilizer (plus leaf mould for water retention), or a proprietary brand of bagged manure can be used. Beds should first be cleared of weeds by scraping with a sharp spade. Loosen the first foot or so of soil with a fork, then top-dress the beds with an inch or so of composted manure or finished compost. When worked into the soil, these amendments will add organic matter and nutrients to your potato beds. Do not add lime to areas of soil planned for potatoes.

Planting

Potatoes are tolerant of cool soils and moderate frost. Planting dates will vary according to region and microclimate, but potatoes are generally planted in early to mid spring.

Set the tubers approximately 7-10cm (3-4") deep and 30cm (1') apart in a prepared trenches spaced 60cm (4') apart. Plants will emerge around 2-3 weeks after planting. When plants are 30cm (1') tall "hill-up" soil 15-20cm (6-8") around the plants (its ok to cover green leaves!). Straw or grass mulch also works well. It is recommended that no irrigation take place between planting and sprout emergence to avoid disease. It is important though, not to let the soil become too dry, and to irrigate (keeping water off of plant tissues) when plants are flowering.

It is important to realise that the potato that we eat grows from a runner that forms from the stem of the plant above the seed potato that you set into the soil. Anything you can do to increase the length of the stem, such as piling more soil against it or planting in a deep trench will allow more runners and potatoes to form. Well-grown potato plants can spread up to 120cm (4') so allow them plenty of room.

Diseases & Pests

Late blight (Phytopthera infestans) is problematic, especially on the Coast. Symptoms appear as water-soaked gray spots on tips and margins of leaves, leaf axils, and on stems. Even if nothing shows on the leaves, late blight makes black spots under the skin of the tuber. Left unchecked, it will destroy the plant. Copper spray is effective if applied regularly through the growing season, including drenching the soil. The most important step to avoiding disease is to establish a vigorous and healthy crop; this can be accomplished by using disease free seed, planting in rich soil, avoiding pre-emergence irrigation and watering carefully once the crop emerges.

The most common pests to bother your potatoes on the coast are wireworms (especially in gardens recently taken out of grass).

Wireworms are the larvae form of a very slender black beetle known as the Click Beetle because if you turn one over, when it goes to right itself, it makes a "Click!" sound. The beetle lays its eggs in grass, and the larvae eat in our gardens. They burrow into the roots, seeds, and underground stems of tomatoes, corn, potatoes, peppers, and squash. The damage is worse on land that has been recently been converted from lawn to garden. The larvae themselves are crisp, golden, up to 1cm long and can live for up to 7 years in the soil.

If your seeds don't appear to sprout, or the plants wilt and die suddenly, your soil may have wireworms. An irregular pattern of plants dying in a field is typical of wireworm damage. To find out if you have wireworms before you start planting, create bait made of carrot and potato pieces. Bury the bait in 10cm of soil, and mark it with a stick. Dig it up in 3 or 4 days. If there are more than 1 or 2 wireworms per bait, you have a problem. They are difficult to control but regular cultivation of the top 10cm of the soil, as well as trapping them on pieces of potato, and crop rotation will slow the damage. Digging in an overwintered Cole crop can also be effective. Predatory nematodes work also.

Harvest

"New" potatoes can be harvested about 7-8 weeks after planting. Potatoes grown for late summer and fall "fresh" use can be dug when tubers are full size or when foliage begins to die. For potatoes grown for storage and winter use, harvest should take place after vines have died back, alternatively, the plants may have to be cut or mown. After killing and removing the plants, tubers should stay in the ground for another 2 weeks to allow firming of their skins for storage. Optimum storage conditions are a dark location 4-7º C (40-45ºF) and 90% relative humidity. Paper sacks stored in a garage will suffice. Check them often though to remove any that are starting to go soft.