When Should I Start My Illinois Vegetable Garden?

When Should I Start My Illinois Vegetable Garden?

It’s time to start thinking about planting your vegetable garden!

For this article, we will gear our information to Central Illinois, but that doesn’t mean if you are in southern or northern Illinois, this information isn’t for you as well. You will just have to adjust the planting times a little to fit your planting zone.

Illinois Planting Zones

The National Gardening Association explains that the USDA Hardiness Zone Map divides North America into 11 separate planting zones; each growing zone is 10°F warmer (or colder) in an average winter than the adjacent zone. 

The Hardiness Zone Map allows gardeners to compare their climate to the climate where particular plants are known to grow well. 

Understanding when the average last date of freeze for your zone is will help you know when to plant certain items.

The most recent USDA Hardiness Zone Map was released in January of 2012 and is different from the prior 1990 version. There are many changes to the map including, zone 4 being completely removed from Illinois.

The changes are due to many factors, including things such as:

  • Data measured at weather stations for a 30 years as opposed to a 13 years for the 1990 map)
  • More sophisticated methods of collecting data such as algorithms that looked at:
    • Land elevation
    • Location of large bodies of water
    • Position on the terrain - valley bottoms or ridgetops
  • Temperature data from multiple weather stations

If you’ve been gardening for years and years, you might want to check this map; it might be a little different than what it was when you first started.

Photo Credit: Illinois State Climatologist

Central Illinois falls on the border of planting hardiness zone 5 and 6. At the same time Northern Illinois is mostly zone 5, except for the Chicago area, which is zone 6 because of “the warming effect of the urban area,”as explained in an article by the Illinois State Climatologist. The Southern tip of Illinois is in zone 7.

When Should You Start Planting Your Garden?

David Sack

To get a reasonable planting timeline for gardeners in the Springfield and Decatur area, we consulted with David Sack, a Central Illinois gardener with 30 years of experience. 

When looking for the best date to begin planting, Sack explains “the gardener really wants the 90th percentile date...because it is more conservative and creates a lower risk that a gardener will plant and then have a killing frost or freeze”. 

An article by Jim Angel, State Climatologist for Illinois, provides a map that shows the 90th percentile frost date for the entire state. 

Photo Credit: State Climatologist Office for Illinois

According to this map, the 90th percentile last frost for the Decatur area is May 6th, and in Springfield, it is April 22nd. That is a two-week difference with just 39 miles separating the two towns, showing the importance of checking the map to make sure you are choosing the best date possible to plant your vegetables.

Sack divided the garden vegetables into three groups based on their optimal planting times: early, mid, and late spring.

  • Early Spring (from seed outdoors): kale, lettuce, onion, radishes, spinach, peas, carrots
  • Mid Spring (from seed outdoors): corn, cucumber, squash, cantaloupe, watermelon

                  (from transplants): cauliflower, broccoli

  • Late Spring (from transplants): brussels sprouts, cabbage, tomatoes, peppers

Through his years of gardening, Sack has found that the following planting dates have worked well for him. These dates are based on the 90th percentile last frost, which we’ll abbreviate as LF.

  • Early Spring: plant one month before LF - April 6 in Decatur and March 22 in Springfield
  • Mid Spring: plant one week before LF - April 29 in Decatur and April 15 in Springfield
  • Late Spring: plant one week after LF - May 13 in Decatur and April 29 in Springfield

Helpful Hints For Planting Your Vegetable Garden

Through our correspondence with David, he offered several helpful hints that we would like to pass along.

  1. When planting spring crops, a frost typically will not damage your crops, but a freeze will.
  2. Look at the ten-day weather forecast before planting and plan accordingly. The above dates are approximate, and your area may be expecting lower than average temperatures, which can push back your plant date.
  3. Pay attention to your soil. Planting in muddy soil is not good. If there is rain in the forecast, plant the day before the rain, or wait until the ground dries.
  4. Use the planting date guide correctly. For example, almost everyone plants lettuce from seed, while hardly anyone plants tomatoes from seed.
  5. Wait to plant peas until the ground is not cold and wet to keep the seeds from rotting.
  6. Lettuce can tolerate a lot of cold and wet and still survive - it’s almost indestructible.
  7. Tomatoes are very tender and should be the last thing you plant - definitely after the last threat of a frost.
  8. If you haven’t ever tried it, you might want to plant watermelons this year. Illinois watermelons are good!

Make Plans for Your Vegetable Garden Now

Yes, it is almost time to plant! Now is the time to plan out your garden. 

Deciding what you want to grow is the first step. Once you know that, you can refer to the Hardiness Planting Zone Map and mark your calendar for the projected planting dates. 

Maybe you’ve had a garden for years, and you want to add new vegetables, or this may be your first garden ever. Either way, with a little planning and knowledge of the best dates to plant, your garden will be off to a great start, and it won’t be long before you can enjoy the fruits - or vegetables- of your labor.

Happy gardening!

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