In our Puget Sound region we plant potatoes on May 1. Soil temperature must be greater than 45-50 degrees F.
Soil for potatoes should be liberally fertilized (6 lbs/100 sq. ft.) with high phosphate fertilizer (eg., 5-10-10) or spread well-rotted manure at the rate of two bushels/100 sq.ft. and provide added phosphate (for example, as bone meal, 1 quart per 100 sq.ft.). pH should be 5-7. Low pH discourages scabbing so avoid applying lime prior to planting. Seed potatoes larger than the size of an egg should be split into egg-sized pieces, taking care that each piece has at least one eye. It is best to allow cut surfaces to ‘heal’ for two days before planting. Seed potatoes should be planted 2.5″ deep, spaced at 18″ with 18″ between rows or with 10″ spacing in rows spaced 3′ apart. Over the course of the summer, covering the base of plants with an additional 4″ of soil and/or organic matter will increase yields and prevent sun-induced greening of exposed potato surfaces.
Plants need to be kept well-watered, especially during the period when plants bear blossums. Young potatoes may be harvested two weeks after blooms appear, but the main crop should be harvested in August, after plants have turned yellow.
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