Is May too late for spring planting?

In northern USDA zones with cooler springs (3-5), specifically, May planting is a suitable option in many climates where frost will linger until spring. I garden in Minnesota, and I consistently have excellent success with Norland potatoes with a planting window of May 10-20. Southern growers have different rules; soil temperatures above 85°F (29°C) will stop tuber growth, irrespective of their schedule. Always compare the variety of potatoes to your frost calendar.

Soil temperature is a key factor, early in May, to successful planting. I stick a grill thermometer down into the soil to a depth of 6". We're looking for 50°F (10°C) as a threshold temperature for soil. The garden in Zone 5b is covered with clear plastic tarps for 10 days before planting. Using this method gave me a 2-week head start in harvest in 2023 exploratory trials.

Gardening in the South can present distinct challenges. Trials in Central Texas have shown that yields of Caribe are reduced by 60% when they are planted after April 20. Simply plant sweet potatoes instead of potatoes. In Coastal California, Russian Banana fingerlings can be planted in late May--with the help of fog--and still produce good yields.

Moisture management is critical. When potatoes are planted in May, we recommend providing 1.5" of irrigation weekly. I use a drip irrigation system that runs for 45 minutes daily (when temperatures are 65 °F). Use straw or similar products as a mulch layer, not grass clippings. Overhead watering can spread blight. I learned about this in 2022 when I lost about 40 potato plants.

Read the full article: When Plant Potatoes: Expert Timing Guide