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Good Growing

Starting a Garden: Warm Season Vegetables

basket with tomatoes, peppers and summer squash

Once the weather starts to warm up, we can start thinking about planting our warms season plants outdoors. Warm season plants can further be broken down by their frost tolerance to tender and very tender plants. Tender plants are injured or may be killed by a light frost but can withstand cool weather, while the very tender, in addition to being damaged or killed by frost, may be injured by cool weather.

So, when can you start putting warm season crops outdoors? First, we need to know when the last frost is. For Jacksonville, it’s April 19 (to find what the last frost date in your area is visit the State Climatologist’s website). This means that there is a 50/50 chance we won’t have any more frosts after the 19th. To be safe, it’s a good idea to wait a week or two after the median last frost to put tender plants outside, and then a few more weeks for very-tender plants.

Plants like bush and snap beans and sweet corn are considered to be tender. These vegetables can be planted outdoors at the end of April/beginning of May. Flowers (annuals) such as ageratum, dianthus, and petunias would also fall into this category.

Warm season plants that are considered very tender are the plants that most people associate with vegetable gardens, such as cucumber, pepper, pumpkin, squash, tomatoes, and watermelons. Flowers like begonia, coleus, vinca, salvia, and zinnia would fit in this group too. These plants are very sensitive to frosts (they’ll be severely damaged or killed) and don’t grow much, if at all, in cool soils. For these plants, it’s best to wait until the middle of May to plant them (temps should be in the 70s during the day and no colder than 50°F at night), unless you want to protect them from frost with floating row covers or plant protectors.

Warm season plants are often started from seed indoors and transplanted (sweet corn and beans would be an exception). If you are going to be starting your vegetables from seed, make sure that you follow the spacing and planting depth suggestions on the seed packets. For more information on seed starting, check out our Good Growing post, or Chris’s video on seed starting.

If you are going to be purchasing transplants, choose the best looking, healthiest plants. What does that mean? Plants should be short, stocky, with a dark green color (color may vary depending on the type of plant) opposed to tall, thin, spindly, and paler colored. Ideally, the plants shouldn’t be flowering either (unless you are purchasing larger, more mature plants). Plants that have insects or disease on them should be avoided. If the plants look like they have been neglected (not watered, haven’t received enough light) pass on those as well.

If your new to gardening here are five warm season plants to try out:

Tomatoes are the most popular garden vegetables in the U.S. There are two ways to classify tomato growth - determinate and indeterminate. Determinate plants tend to be smaller plants (generally 3-4 feet tall), which makes them good candidates for growing in smaller gardens or pots. The plants will grow to a certain point, produce flowers, and the tomatoes will ripen around the same time. Indeterminate plants will continue to grow and produce tomatoes throughout the growing season. Because they continually grow, indeterminate type plants can get rather large and should be grown with some sort of support (staking or trellising). When deciding what type of tomato to grow, it’s best to start with a hybrid variety. Hybrids tend to have better disease resistance than heirloom types. Cherry tomatoes also tend to have fewer disease problems than other types of tomatoes (paste, slicing, beefsteak, etc.).

Peppers are another popular plant to grow in a vegetable garden. Sweet peppers, particularly bell, are the most commonly grown peppers. These peppers don’t produce any ‘heat’. Hot pepper varieties are growing in popularity and can range from mild to extremely hot. The Scoville scale was developed to measure the heat or spiciness of peppers. Bell peppers are a 0 on the scale, jalapenos are 2,500 – 8,000, and the hottest pepper in the world, the Carolina Reaper, is 2.2 million! Peppers are related to tomatoes, and their growing requirements are similar. They do require somewhat higher temperatures, grow more slowly, and are smaller than most tomato plants though.

Beans are the second most commonly grown vegetable in the U.S. Beans can be either bush or pole type. Bush beans are smaller, bushy plants that don’t require any support and, therefore, less work. Pole beans are vines and require some sort of support (trellis or fence) but are easier to harvest. Harvest green beans when they are firm, crisp, and fully elongated, but before the seeds have developed a lot. If you are growing dry beans, such as kidney or great northern, they are harvested when the pods dry out.

Cucumbers can be seeded directly into the garden (soil temperatures above 70°F), or they can be transplanted. Cucumbers are a vining plant and many varieties require a significant amount of room. If space is an issue, plants can be trellised or look for bush varieties that take up less space. When you harvest cucumbers will depend on your intended use for them and the variety. Pick cucumbers you plan to pickle when 2 inches long or smaller, 4 to 6 inches long for dills, and 6 to 8 inches long for slicing varieties.

Squash are also vining plants that need a lot of room to grow. However, there are some bush varieties, such as bush zucchini and bush yellow summer squash that require less room. Squash are typically classified as summer or winter squash. Summer squash (such as crookneck and zucchini) are harvested while the skin is still soft (before the fruit matures). Winter squash (such as acorn, delicata, and butternut), on the other hand, are not harvested until the skin hardens and the fruits mature.

Crop Recommended planting period for central Illinois*
Beans (snap) April 25 - July 15
Corn (sweet) May 1 - July 9
Cucumber May 10 - June 15
Eggplant May 10 - June 15
Muskmelon May 10 - June 15
Okra May 10 - June 15
Pepper May 10 - June 15
Pumpkin May 20 - June 10
Squash (summer) May 10 - June 15
Squash (winter) May 20 - June 1
Sweet potato May 10 - June 15
Tomato May 10 - June 15
Watermelon May 10 - June 15
*For southern Illinois approx. 2 weeks earlier, for northern Illinois approx. 2 weeks later 


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