This is the latest that gardeners can plant a radishes and spinach. Otherwise, they will quickly bolt in June and July. Peas, parsnips, carrots, cabbage, lettuce, mustard greens, swiss chard, and potatoes can also be planted now if the soil is warm.
Shallot and onion bulbs can be planted into cool, moist soil now. But other vegetables like tomatoes, cabbage, cauliflower and broccoli should be started indoors over the next few weeks before transplanting them outside.
One option is to bring potted plants into a garage or other protected space. Alternatives for garden plots include gently covering plants with old blankets or cardboard boxes. That will provide insulation for retaining heat close to the soil.