Domhanda: Tugann Píosaí Síolta 1.5–2.5 Unsa na Torthaí is Fearr i bPlandáil Prátaí

Seed piece size is one of the cheapest yield levers in potato growing. In most cases, pieces of 1.5–2.5 ounces give the best returns, according to a University of Idaho bulletin. That is about 43–71 grams. Above about 2.5 ounces, the benefit of larger pieces diminishes.

University of Maine Cooperative Extension gives a similar range. It recommends 1.5–2 ounces for most varieties. For Russet Burbank, pieces should average slightly larger, at 2–2.5 ounces. Growers should avoid pieces smaller than 1.5 ounces or larger than 3 ounces. At least 70% of pieces should fall within 1.5–3 ounces.

The cost of small seed

Small pieces carry limited reserves. The Idaho bulletin gives an example. If just 10% of seed by weight is under 1 ounce, about 20% of the planted area has weak pieces. Undersized seed reduces yields in Idaho by an average of 50–60 cwt per acre. That equals roughly 5.6–6.7 t/ha.

Seed size also sets the seed bill. The Idaho bulletin lists seed rates at 9-inch spacing. They are 18.2 cwt per acre for 1.5-ounce pieces and 24.2 cwt for 2-ounce pieces. Pieces of 2.5 ounces need 30.3 cwt. The Maine guide gives 20.2 cwt per acre for 1.75-ounce pieces at 34-inch rows and 10-inch spacing. That equals 18,449 seed pieces per acre.

Stems decide tuber numbers

Stem number drives tuber set. As stem number increases, so does tuber number, according to North Dakota State University (NDSU). For Russet Burbank, an average of 2.5–3.5 stems per plant is considered optimum, the Idaho bulletin says.

Physiological age changes stem numbers. Older seed usually emerges faster and produces more stems per hill. It also gives a higher tuber set and smaller tubers. Young seed produces plants with few stems, the Maine guide says.

Stress speeds up seed ageing. Heat, drought, poor fertility, disease and bruising all age tubers faster, NDSU says. Storage at 38°F (3°C) slows ageing. Storage at 50–55°F (10–13°C) speeds it up. A grow-out test of 100 seed pieces shows stem numbers before planting. The test takes 3–4 weeks.

Cén fáth a bhfuil sé tábhachtach

Choosing the right seed size affects both the seed bill and the final yield. Too small cuts yield. Too large raises the seed bill with little extra return.

Stem number links seed to market. Growers who know their seed age can target the tuber size their buyer wants.

Photo: Planting seed potatoes (illustrative). Philippus Jacobus Steyn / Cómhaoin Wikimedia, CC BY-SA 4.0