Squeezing a second crop of vegetables in before fall frost makes good use of garden space. Once spring crops are harvested, fertilize and prepare the soil for summer planting.
The following suggestions for summer planting are made based on the mid-October average killing frost date for Denver, but you should check the last frost date for your area before trying these suggestions. Remember that Colorado's weather varies from year to year and frosts may come as much as a month earlier or later.
Crops that can be planted until mid-July include cabbage, collards, endive, green onions, New Zealand spinach, bush beans, cucumber, cauliflower, edible-podded peas and summer squash.
Vegetables that can be planted until the end of July include Chinese cabbage, small length carrots like the Nantes varieties, broccoli and turnips.
Vegetables that will produce crops if planted until early August are kale, turnip greens and beets. Crops that produce until mid-August are leaf lettuce, mustard greens, spinach and Swiss chard. Radish can be planted as late as the first week of September.
Many greens make particularly good late crops as they can be harvested at any stage of growth.
For more information, see the following Colorado State University Extension fact sheet(s).
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Updated Monday, February 22, 2016