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The demand for small, gourmet, fresh market potatoes has increased in recent years. Production of small potatoes can be enhanced through management, although tuber size and number is not entirely under the grower’s control. Producers wishing to grow for this specialty market can follow a production plan to produce small potatoes, or they can grade out the small tubers from a mixed size tuber lot. Several factors contribute to small tuber size.
- Crop stress due to under-fertilization or low soil moisture.
- Short growing season due to early harvest (70 to 90 days after planting) or late planting.
- Tuber set – More tubers per individual plant results in increased competition.
- Plant population – A high plant population produces more daughter tubers per acre (hectare) resulting in increased competition.
The first two factors result in reduced yields and immature tubers, which may not store well. The last two factors result in an increased number of smaller daughter tubers without sacrificing total yield. Growers should employ management practices that increase tuber set and plant population to achieve smaller tubers. These include the following practices, which are discussed below:
| Controllable input | Specific recommendations | Comments |
| Variety |  | Early, naturally tend to set high |
| Seed type | Whole 2 to 4 oz (60 to 120 g) seed preferred | small tubers can be cut if whole seed is not available. Seed pieces cut from larger seed tubers should be a minimum of 2 oz (60 g) larger. |
| Seed tuber sizes | 2 to 4 oz (60 to 120 g) | Small seed tubers or small pieces result in low stem numbers per plant and therefore low tuber numbers. Small seed pieces (<1.5 oz or 40 g) produce weak, unproductive plants and should be culled. |
| Seed warming | Warm seed for two or more weeks prior to planting to ensure that the eyes are starting to peep. | If the weather turns bad near the scheduled planting date, seed tubers can be cooled to prevent excessive sprout growth prior to planting. |
| Green sprouting or chitting. (Widely used in Europe, primarily for the early market, but will also increase tuber numbers per plant.) | Eight weeks before planting seed tubers are warmed to 68°F (20°C). Seed tubers are then placed in flats or mesh bags in light for two weeks prior to planting. Plants emerge early and set heavy. | Tubers, which are green sprouted 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. Green sprouted seed develops earlier and may be useful for production of early season small potatoes. |
| Planting date and vine killing | Plant as soon 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. Local experience will dictate best "days to harvest" period, however small potatoes should be ready for harvest between 70 and 90 days, depending on variety, tuber set, fertility and moisture. High tuber populations will delay sizing. | Planting of potatoes for storage should be delayed because of the risks of killing vines very early. If a crop is planted early, tubers will be of (small) marketable size by mid to late July. If they are vine 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 applications of fertilizers should be based on soil test results. | Tissue tests should be taken to assess nitrogen status during the growing season and nitrogen should be added through the irrigation water as required Potatoes deficient in nitrogen are susceptible to early blight and will die prematurely. |
| In-row and inter-row spacing | Space seed tubers or pieces 6" (15 cm) apart in the row. Rows should be 35" (90 cm) apart. | Growers who wish to produce small tubers for the early market in July when prices are high can space seed pieces farther apart in the row. Potatoes for later markets should be spaces at the recommended distances. |
| Irrigation | Irrigation is strongly recommended for this intensive production. Maintain soil moisture above 65% of the available soil water (ASW) 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 adequate supply of natural water. However, yields and quality will be consistently higher in most areas and years when supplemental water is applied. |
Variety selection
Certain varieties tend to produce higher tuber numbers (set) than others. For example: Cal Red and Bintje produce a large set, making it suitable for gourmet tuber production. For more information on tuber set characteristics of individual cultivars, refer to the Variety Description section.
Seed size
Large, whole seed pieces, between about 2.5 and 3 oz (70- 90 g), produce more stems per plant than smaller seed or cut seed. Tuber set (number) is directly related to stem number, therefore the higher the stem count per plant, the higher the tuber set. Growers producing small whole tubers under irrigation should aim to have at least four or five stems per linear foot of row.
Seed handling
Seed that is warmed or aged prior to planting will produce higher tuber sets than cold or young seed. Warming seed at 50-53°F (10-12°C) for two weeks (or more) prior to planting is recommended. Seed can also be aged by maintaining storage temperatures slightly higher than normal (41°F instead of 37°F or 5°C instead of 3°C) 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 set potential of potato seed tubers.
Green sprouting
Green sprouting, or chitting, is a used to accelerate the emergence and development of potatoes and to increase tuber numbers. Eight weeks prior to planting, seed tubers are warmed to 68°F (20°C) in the dark to promote multiple sprout development. When the white sprouts are 2 to 3 mm long, the seed is exposed to light for 8 to 10 hours per day for two weeks. Seed tubers are placed in wooden trays or mesh bags that are made especially for green sprouting. Green sprouting seed tubers will form short, thick, sturdy, green sprouts, which will remain intact during planting.
Irrigation
Research studies have shown that moderate soil moisture stress during tuber set (tuberization) results in significantly lower tuber numbers. Tuberization begins when potato plants are 6-8" (15-20 cm) high. Maintaining soil moisture at or above 65% of the available soil water (ASW) capacity, when the plants are between 6" (15 cm) high results in a high tuber set. By the time the potato plants begin to flower, stem numbers and soil moisture have established tuber number.
Plant spacing
Increasing the in-row population results in more stems and tubers per acre (hectare). This increases the competition for nutrients, moisture and sunlight resulting in smaller tubers. Growers who strive for high yields of small tubers should plant potatoes 6" (15 cm) apart. Yields of most varieties increase as in-row population increase. Increasing plant populations also increases the demand for fertilizer and water.
Written by L. Delanoy and C. Schaupmeyer |
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