Many gardeners assume that the gardening season is over once the first frost hits. But in Idaho, that’s not always true. Whether you live in the mild Treasure Valley, the high deserts of eastern Idaho, or the cooler northern panhandle, you can still start or extend a garden this time of year with the right techniques.
Cool-season crops are your best bets
When planting in late summer or early fall, focus on vegetables that thrive in cooler temperatures and can handle light frost. Examples include leafy greens like spinach, lettuce, kale, and Swiss chard, as well as root crops such as radishes, beets, and carrots (Idaho Master Gardener Program, n.d.). Broccoli, cauliflower, and cabbage can also perform well if planted early enough to mature before hard freezes set in.
One effective approach is succession planting—sowing a new round of seeds for crops like lettuce, radishes, and spinach every two to three weeks. This staggered planting schedule can keep a steady supply of fresh produce coming until frost, and when combined with season extension methods, can even push the harvest into late fall (University of Idaho Extension, 2009).
Know your planting dates
Timing is critical in Idaho’s diverse climates. The University of Idaho Extension emphasizes basing your planting schedule on both your area’s average last spring frost and first fall frost, and adjusting for elevation and microclimates. For example, while parts of southern Idaho may not see frost until late September or early October, northern and higher-elevation regions can face frost as early as late August.
Knowing your local frost window allows you to select vegetable varieties with a days-to-maturity that fits your growing season. Choosing varieties adapted to Idaho’s short-season and high-altitude conditions—such as certain leaf lettuces, cold-tolerant spinach, and early-maturing onions—is key to maximizing harvest before frost (University of Idaho Extension, 2009; NOAA, 2024).
Use season extension tools
If you want to keep your garden producing longer, consider season extension methods:
Row covers and low tunnels made of lightweight fabric can protect plants from light frosts and extend your season by several weeks. Cold frames create a small, greenhouse-like environment, capturing daytime warmth and protecting crops at night. High tunnels or hoop houses can allow for late fall and even winter gardening, particularly in southern Idaho.
Research shows that even simple covers can increase the temperature around plants by several degrees, making the difference between harvest success and frost damage (University of Idaho Extension, 2022).
Adjust your watering practices
As temperatures drop and days shorten, plants use less water. Overwatering in cool weather can lead to root diseases. Water deeply but less frequently, focusing on maintaining consistent soil moisture for root crops and greens. Drip irrigation or soaker hoses work well for this purpose and minimize water waste — a key consideration in Idaho’s arid regions.
Choose the right varieties
Selecting fast-maturing or frost-tolerant varieties is crucial for fall planting. Look for seed packets labeled “cold hardy” or “frost tolerant.” In Idaho, proven performers for late planting include ‘Winter Density’ lettuce, ‘Bloomsdale Long Standing’ spinach, and ‘Scarlet Nantes’ carrots. If you’re planting brassicas, opt for shorter-day varieties to ensure harvest before heavy frost.
Think beyond this season
Late summer and fall are also excellent times to prepare garden beds for next spring. Add compost, plant cover crops like winter rye or clover, and mulch perennials to protect them over winter. By investing effort now, you’ll get a head start when the soil warms again.
Bottom line
Yes, you can start a garden now in Idaho — but success depends on choosing the right crops, knowing your local frost dates, and using season extension techniques. With careful planning, your garden can produce fresh vegetables well into fall, and you can even
prepare for a strong start next spring.
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