Small, gourmet, fresh market potatoes are rising in popularity with consumers. Production of small potatoes is fairly straight forward, although not entirely controllable. Producers wishing to grow for this speciality market should follow a plan to grow small potatoes versus removing the small tubers from a mixed lot.

Why do small tubers happen? The majority of small tubers are small for many reasons:

Early crop death due to disease or under fertilization.
Early crop death by spraying vines with a chemical defoliant or mechanical killing.
High tuber numbers under individual plants which increases competition.
High plant populations within the row which increases competition.

The first two points are undesirable because they reduce yields. Early dying from disease and low nutrition may also reduce tuber quality. Planned early crop destruction by chemical or mechanical killing may be used to control size, however crops killed too early may not store well. For size control, it makes more sense to increase tuber populations by increasing tuber set (number) per plant and increasing plant population.

Some varieties tend to produce higher tuber numbers than others. There are reports of one or two varieties from the Netherlands that set high numbers of tubers per plant (50+), however they are not registered in Canada. Efforts are being made in the Western Canada Potato Breeding Program to select varieties that produce high sets and, therefore, result in high yields of small tubers.

Several controllable inputs will increase tuber numbers under individual plants or within a given length of row.

Large, whole seed pieces produce more stems per plant than smaller seed or cut seed. Tuber set is directly related to stem number; therefore, the higher the stem count per plant, the higher the tuber set.
Seed that is warmed or aged prior to planting will produce higher tuber sets than cold or young seed. Warming seed at 10 or 12^oC for two weeks prior to planting is mandatory. Seed can also be aged by maintaining storage temperatures slightly higher than normal (5^oC instead of 3^oC) for two to four months during the storage period, however this may result in sprout growth prior to planting time. Seed age is also affected by the warmth and length of the growing season the year before. It is difficult to establish the exact tuber setting potential of potato seed tubers.
When plants are between 15 and 30 cm tall, high moisture is critical to high tuber set. Studies have shown that moderate dryness during tuber set (tuberization) results in significantly lower tuber numbers. Contrary to popular belief, tubers start forming when potato plants are about 15 to 20 cm high. Soil moisture at or above 75 percent of available capacity, when the plants are between 15 cm high and blooming, results in a higher tuber set. By the time potatoes have bloomed (which is when many people think tubers are forming), the tuber set has already been established by stem numbers and soil moisture.
Increasing the in-row population results in more stems (and tubers) in the row. Therefore, competition for nutrients, moisture and sunlight is increased, reducing the size potential of each tuber. Growers who strive for high yields of small tubers should plant potatoes at 15 cm apart in the rows. Yields of most varieties increase as in-row populations increase. Seed requirements are high at these high populations.

Specific recommendations for the production of small potatoes for mid- and late-season (storage) markets

Production of Small Potatoes for the Fresh Market

Controllable input	Specific recommendations	Comments
Seed type	Whole 60 to 120-g seed preferred.	Larger seed tubers can be cut if whole seed is not available. Seed pieces cut from large seed tubers should be a minimum of 60 grams, but preferably larger.
Seed tuber size	60 to 120 grams	Small seed tubers or small pieces result in low stem numbers per plant and, therefore, low tuber numbers. Small seed pieces (<40 grams) produce weak, runty, unproductive plants.
Seed warming	Warm seed for two weeks or more prior to planting to ensure that the eyes are starting to peep.	If the weather turns bad near the scheduled planting date the seed tubers can be cooled down in storage to prevent excessive sprout growth.
Green sprouting (Widely used in Europe primarily for the early market, but will also increase tuber numbers per plant.)	Place seed tubers in flats not more than two tubers deep. Place flats in full sunlight in a warm greenhouse or outside for two weeks prior to planting. Plants emerge early and set heavy.	Tubers set in light outside must be protected from evening frosts with covers or by moving indoors at night. Seed tubers exposed to warmth and sunlight will start to sprout. However, the sprouts will remain short as the light prevents sprout elongation.
Planting date and vine killing	Plant early as possible for early and mid-season small tubers. The planting date for small potatoes going into storage should be delayed until late May or early June.	Planting of potatoes for storage should be delayed because of the risk of killing vines very early. If a crop is planted early, the tubers will be of marketable size by mid to late July. If they are top killed (chemically or mechanically) at that time, the small tubers may overheat in the soil. This can cause excessive moisture loss from the tubers and make them vulnerable to disease at harvest. When tops are killed early, soils do not dry well after late summer rains, again making the tubers prone to disease.
Fertility	Pre-plant application of fertilizers should be based on soil test results. However, a general recommendation for high yields of irrigated late-season small tubers is: nitrogen = 200 pounds/ acre; phosphorous = 150 pounds/acre; potassium = 100 pounds/acre; sulphur = 30 pounds/acre. (Earlier crops will require lower rates.)	Tissue tests should be taken to assess nitrogen status during the growing season. Nitrogen should be added through the irrigation water as required. Potatoes deficient in nitrogen will die early and are very susceptible to early blight, which will hasten total plant death and may result in tuber rot.
In-row spacing	Space seed tubers or pieces 15 cm apart in the row. Rows should be about 90 cm apart.	Growers who wish to produce small tubers for the early market in July, when prices are high, will space seed pieces farther apart in the row. Potatoes for later markets should be spaced at the recommended distances. Seed requirements for a 15 cm in-row spacing are about 4,000 pounds per acre for 60-g tubers and about 5,500 pounds per acre for 90-g seed tubers.
Irrigation	Irrigation is strongly recommended for this intensive production. Maintain soil moisture at about 75 percent of available capacity from the time of emergence to harvest.	Dryness at any time during tuberization will reduce tuber numbers dramatically. Small tubers can be grown without irrigation where there is an adequate supply of natural water. However, yields will be consistently higher (and quality much better) in most parts of Alberta when required supplemental water is applied.

Information prepared by: Clive Schaupmeyer P.Ag, CDC-South, Brooks, Alberta The contents of this page are no longer available.

For more information about the content of this document, contact Shelley Barkley.
This information published to the web on June 19, 2002.
Last Reviewed/Revised on March 5, 2007.