Home Food Garden: Growing Real Food, Season After Season

By GoldBlock WorkshopPublished Updated

The short answer

The USDA hardiness zone is “the standard by which gardeners and growers can determine which perennial plants are most likely to thrive at a location”; planting dates come from local frost dates and soil temperature (University of Minnesota Extension: 40 to 50°F for cool-season direct seeding, 50 to 60°F for warm-season crops). The extension sources below cover soil testing, manure safety (120 days before harvest for crops that touch soil), succession planting, seed saving from open-pollinated varieties, and the sprout warning.

Key numbers

Hardiness zones and frost dates

USDA describes its Plant Hardiness Zone Map as “the standard by which gardeners and growers can determine which perennial plants are most likely to thrive at a location.” It is based on “the average annual extreme minimum winter temperature, displayed as 10-degree F zones and 5-degree F half zones.” Find yours by ZIP code on the USDA map.

The map’s basis is winter minimum temperature, not the growing season. University of Minnesota Extension times planting by soil temperature and the last frost (below). Colorado State University Extension (Irene Shonle, December 2020): “For every 1000 feet gain in elevation, the temperature drops by an average of 3.5° F,” and “valleys may actually have cooler growing conditions than surrounding hillsides.”

Cool-season and warm-season crops

University of Minnesota Extension (reviewed 2026):

  • “If soil temperatures are between 40 and 50 degrees F, you can direct-seed peas, spinach, lettuce, and radish.”
  • Warm-season crops “need soil temperatures between 50 and 60 degrees F”; “Wait until after the last frost (mid-to-late May) before transplanting tomatoes, eggplants, peppers” (the dates are Minnesota’s).

Succession planting: harvest all season

University of Minnesota: “Some vegetables can be planted twice in a growing season,” with leaf lettuce, radishes and kohlrabi planted “in mid-April and again in August for an additional harvest in fall.” Colorado State University Extension: “plant smaller amounts every two weeks or so.”

Soil testing and building

University of Minnesota Extension: “A soil test will tell you if you need to add any lime, nitrogen, phosphorous or potassium to your soil.”

Garden water

Iowa State University Extension (reviewed July 2026): “Drip irrigation is one of the most efficient watering methods,” using 30% to 50% less water than traditional methods, and “Keeping foliage dry also helps reduce disease problems”; mulch “is a great way to conserve soil moisture, reducing the amount of irrigation needed.” On harvested rainwater, Rutgers Cooperative Extension (FS1218, 2013): “Harvested rainwater should only be applied to the soil, possibly through drip irrigation”; “harvested rainwater can not normally be used as a source of drinking water”; “Produce harvesting should not take place right after watering”; “At a minimum, E. coli testing should be conducted,” with testing sometimes required under state or federal guidelines. UConn Extension (Joan Allen, May 18, 2018): “Rain barrel water should NEVER be used for potable purposes such as drinking water, cooking or washing”; its specialist advises “not using roof water on anything leafy that you are going to eat directly”; “Thoroughly wash all harvested produce.” For drinking water, see Water Preparedness.

Season extension

Colorado State University Extension: floating row covers can gain “a couple weeks of growing on either side of the season,” low tunnels “can increase the growing season by a month at either end,” and cold frames “will need to be ventilated on sunny days or temperatures may rise enough to kill plants.”

Seed saving

University of Minnesota Extension:

  • Open-pollinated varieties “set seed that grow into plants that are still very similar to the parent plant”; for hybrids, “Plants grown from that seed are not identical to the hybrid parents.”
  • Tomatoes, peppers, beans and peas, whose flowers self-pollinate, are “good choices for seed saving.”
  • For biennials such as carrots and beets, “the plants need two growing seasons to set seed”; “Plants with separate male and female flowers, like corn and vine crops, may cross-pollinate.”
  • Store seed in “tightly sealed glass containers” at 32° to 41°F (a refrigerator), and use it within a year, since germination and vigor decline with age.

Indoor growing and sprouting

University of Vermont Extension (Andrea Knepper, January 8, 2025): “You can easily grow fresh sprouts at home in a few days with minimal supplies,” rinsing and draining the seed “twice per day for three to six days.” Sprouts also carry a food-safety risk that the FDA and UConn describe:

Growing for a food plan

The crops with months-long storage figures from University of Minnesota Extension (potatoes, winter squash, onions, carrots, beets, cabbage and other roots) are in Root Cellars and In-Ground Storage; perennial food is in (Perennial Food and Edible Landscaping), and preserve the surplus (Food Preservation).

Common questions

What is my growing zone, and what does it tell me?

The USDA map is based on “the average annual extreme minimum winter temperature” and is “the standard by which gardeners and growers can determine which perennial plants are most likely to thrive at a location.” Planting dates come from soil temperature and the last frost (University of Minnesota).

When should I plant my garden?

University of Minnesota: cool-season crops can be direct-seeded at soil temperatures of 40 to 50°F; warm-season crops need 50 to 60°F; tomatoes, eggplants and peppers are transplanted after the last frost.

How do I get a harvest all season long?

Colorado State University Extension: “plant smaller amounts every two weeks or so”; University of Minnesota: leaf lettuce, radishes and kohlrabi “in mid-April and again in August for an additional harvest in fall.”

What are the rules for using manure in a vegetable garden?

University of Maine Extension: “Apply raw manure at least 120 days before harvesting a crop that has the potential for soil contact”; compost reaching 140°F further reduces the risk; “Never use cat, dog, or pig manure in vegetable gardens or compost piles”; “All produce should be washed very well before you eat it.”

Can I save seeds from store-bought hybrid vegetables?

University of Minnesota: for hybrids, “Plants grown from that seed are not identical to the hybrid parents”; open-pollinated varieties “set seed that grow into plants that are still very similar to the parent plant.”

Where to go next

Sources