Plants can be classified by the temperatures that produce optimum growth.
Plants can be classified by the temperatures that produce their optimum growth. The two main categories of plants based on temperature are cool-season and warm-season. Many cool-season crops have edible leaves or roots (spinach, carrots, lettuce, radishes). Others such as artichokes, broccoli, and cauliflower are grown for the immature flowers. A few produce edible seeds (peas and broad beans).
Many cool-season vegetables can be started much earlier than the end of spring. Cool temperatures in spring usually means fewer pests present to damage vegetables. Many crops can tolerate colder weather and soil and can be planted as early spring vegetables. Unlike warm-season crops, cool-season crops should be planted so that they mature when the weather is still cool and before summer heat arrives. When warm weather arrives, many of these early crops tend to “bolt” which means they prematurely go to seed. These crops flourish in temperatures lower than 70 degrees Fahrenheit so planting their seeds or transplants in early spring will help ensure a healthy, productive harvest. Which spring garden plants to grow and when to plant them depends on where you live. The USDA Plant Hardiness Zone Map is based on a location's average annual minimum winter temperature and is divided into 10-degree Fahrenheit zones. It offers established guidance about which plants are likely to thrive in a given location.
Cool-season vegetables grow best at temperatures ranging between 40-75 degrees Fahrenheit. These crops are often divided further into categories of hardy and semi-hardy depending on their ability to withstand cold temperatures. Old-time gardeners didn't grow vegetables for fun. They fed themselves and their families with homegrown food. Two dates have traditionally been very important on traditional spring gardening calendars: St. Patrick's Day and Mother's Day. The old-time wisdom to "plant your potatoes around St. Patrick’s Day and don’t put your tomatoes out before Mother’s Day" still holds true.
Hardy vegetables tolerate cold temperatures the best since their seeds will germinate in cool soil and seedlings can typically survive heavy frost. Plant these seeds or transplants two to three weeks before the date of your average last spring frost. Semi-hardy vegetables will withstand light frost. These crops grow best when the minimum daytime temperature is between 40- 50 degrees Fahrenheit and can be sown as early as two weeks before the average last spring frost. Some cool season crops fare better when direct-seeded while others can be started indoors.
Warm-season crops grow optimally in higher temperatures than cool-season crops. This is because the growing season when the temperature is warm enough for these crops to be planted in the garden is often too short for the plants to mature from seed. Cool-season crops can often be planted and produced in two growing seasons: early spring (sometimes prior to the last frost) and early fall. They must be planted early enough in the spring to reach maturity before temperatures become too warm. The seeds require cool temperatures to germinate in the fall. In warm locations, plant cool season crops from late summer to early fall for harvest in late fall, winter, and early spring. In cold-winter regions, cool season crops should be planted in May or June for summer harvest.
(https://www.sunset.com/garden/garden-basics/cool-season-crops-0; https://extension.psu.edu/cool-season-vs-warm-season-vegetables; photos-top to bottom: [email protected]; [email protected]; Serhiy [email protected]; [email protected]; Brent [email protected]; Picture [email protected]; [email protected])