When to Plant Cabbage in Boulder

Can Cabbage Mature in Boulder?

Growing degree days measure how much useful warmth typically accumulates during the season. For cabbage, this helps estimate whether local heat accumulation is usually enough for the crop to reach maturity on time.

From the usual planting window, Boulder typically provides about 4211 growing degree days for cabbage. With a typical crop target of 1000, that leaves a heat margin of +3211. That large heat margin means the crop usually has no trouble reaching maturity here. In practice, planting timing mostly affects how comfortably the crop sizes up and when harvest is ready, not whether the crop can finish.

When Is It Too Late to Plant?

If planting later than usual, this table shows how much growing degree day heat is still available from each point in the season. For cabbage, it is most useful for judging how much freedom you still have to plant for quality, finish, and harvest goals as the season moves along.

How Different Cabbage Varieties Affect Results

Most cabbage varieties can succeed in Boulder in a typical year. That gives gardeners room to choose for the kind of harvest they want, not just for minimum maturity speed.

Varieties that often fit well here include:

• Golden Acre — a classic early cabbage with strong practical fit in shorter seasons
• Early Jersey Wakefield — an early pointed cabbage that is useful when speed and spring harvests matter more than storage
• Stonehead — reliable and approachable, especially where gardeners want a firm early head
• Red Express — a faster red cabbage option for gardeners who want color without moving all the way into long-season storage types
• Cheers — productive and strong where the season offers a comfortable cool run
• Storage No. 4 — better suited where the growing window gives longer room for finishing

Main risk: The usual setbacks here come from management choices rather than from the season itself.

How Frost Affects Planting Dates for Cabbage in Boulder

Boulder usually has about 152 frost-free days, with a typical last spring frost around May 6 and a typical first fall frost around October 5.

Cabbage is generally somewhat frost tolerant and temperatures below about 28°F ( -2 °C) can slow growth or damage plants.

Cabbage is usually tolerant enough of cool conditions that light frost is not the main concern. The more useful question is how early planting affects establishment and overall crop quality.

The most common problems here are not climatic ones. Gardeners usually lose ground through timing, uneven growth, or letting the crop move past its best stage.

In Boulder, cabbage usually has a solid seasonal margin when planted around April 15. The warmest garden spots are usually south-facing walls, sheltered gardens, raised beds, and sunnier urban lots. Cooler spots like low spots, exposed sites, and shadier yards tend to warm up later and usually provide less heat. For cabbage, warmer garden spots usually improve early growth and can make timing a little more forgiving.