It’s February already. Days are longer and happily, it will soon be planting time. According to the U.S. Department of Agriculture Plant Hardiness Zone Map, most of us will be relatively safe planting based on Zone 6b, with temperature lows ranging from -5 to 0 degrees Fahrenheit.
The USDA Plant Hardiness Zone Map is based on the average annual minimum winter temperature, divided into 10-degree Fahrenheit zones. If you prefer the Sunset Western Garden Book zoning system, we are a Zone 2b with minimums averaging from 12 degrees to 22 degrees F and infrequent extremes in the -10 degrees to -20 degrees F range. I find the Sunset system more accurate, because it is based not only on temperature but also on heat, humidity, wind, snow cover and length of growing season.
No matter which zoning system you prefer, planting dates depend on plant hardiness. Some vegetables are hardy and can be planted as soon as the soil can be worked in the spring. Their seeds will germinate in cool soil, and seedlings can typically survive heavy frost. Usually these seeds or transplants can go in the ground two to three weeks before the date of the average last spring frost.
In west Washoe Valley where I live, late May to June 1 is our last frost. In much of Reno, Carson City and Douglas County, the last frost date can be as early as the first week of May. Since every area has its own microclimate, ask a longtime resident what the average last frost date is.
In warmer areas, some vegetables can be direct-seeded from March 15 until May 1. These include asparagus crowns, broccoli, Brussel sprouts, cabbage, chives, collards, garlic cloves (although fall planting is best), horseradish (restrict spread!), kale, spinach and sweet peas (traditionally planted on St. Patrick’s Day). These very hardy vegetable seedlings will grow in daytime temperatures as low as 40 degrees F.
One thing we have to always remember is that our Northern Nevada weather is fickle. We can have beautiful 40- to 50-degree days with occasional highs reaching the low 70s, followed by stormy days barely into the 30s in late winter and spring. Even cold hardy seedlings can be tender at early stages when hit by a sudden severe cold snap.
If you do plant as early as mid-March, plan on mulching heavily or covering seedlings with row covers, if a storm or freeze is predicted.
JoAnne Skelly is associate professor and Extension educator, Emerita at University of Nevada Cooperative Extension. She can be reached at firstname.lastname@example.org.