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Saturday, April 20, 2024

When to Plant Your Vegetables

By: Kathy Roth Colorado State University Extension Master Gardener in Larimer County

Growing your own vegetables allows you to truly understand what “fresh” means. Even if you have a small garden area, or plant your veggies in containers (like I did on my apartment balcony back in the ‘80s), you can reap the rewards of homegrown produce. Growing vegetables in Colorado necessitates understanding that we have challenges—temperature swings, cold spring winds, a short growing season, hailstorms and desiccating hot summer winds. Though the elements may conspire against us, persevere (and use mulch to conserve moisture)!

An important date to keep in mind is May 15; Northern Colorado’s average frost-free date. If you try to outsmart Mother Nature by putting your tomato plants out on a summer-like day in April, heed caution. They may freeze on a frosty night or likely won’t survive one of our typical spring snowstorms—replacing plants can get expensive, so it’s better to wait.

Vegetables are classified as either cool or warm season crops. This description refers to the temperature conditions under which veggies grow best. Successful harvest for cool season crops depends on the plants maturing while the weather is still cool. Hot weather may cause bitter tasting lettuce or cause your broccoli to “bolt” (go to seed) instead of being edible.

General guidelines for planting vegetables can be garnered by reading the backs of the seed packets and by checking the Colorado State University Extension Master Gardener “Garden Notes” #720: “Vegetable Planting Guide”. This publication can be found online at  “” along with other gardening information. The guide outlines the optimal planting dates of many vegetables, as well as planting instructions concerning seed depth, spacing and typical days to harvest. These planting time guidelines are based on the temperature needed for seed germination. If soil temperatures are not warm enough, the seed will not germinate.

Another problem with cool temperatures is that they may stunt a young plant if transplanted outside too soon. If you are transplanting purchased plants or ones that you have started indoors from seed, be sure to “harden off” the plants first. This process lessens the shock of moving them from indoors to outdoors by gradually exposing seedlings to longer periods of outdoor temperatures (unless temperatures are below 50° F) over a period of at least a week. Reducing the seedlings’ water will also help plants adjust to outside conditions.

Hardy Cool Season Vegetables can be planted first, as early as 2-4 weeks before the average last spring frost date of May 15. These vegetables include broccoli, cabbage, onions, lettuce, peas, radish, spinach and turnips. They prefer cool growing temperatures and fail to thrive in summer heat.

Semi-Hardy Vegetables are less able to withstand a cold night and can be planted up to 2 weeks before May 15. These include beets, carrots, cauliflower, parsley, parsnips, potatoes and Swiss chard.

Tender Vegetables like beans, celery, corn, cucumbers and summer squash need to wait until after May 15 and in many cases should be planted toward the end of May. The very tender vegetables like tomatoes, peppers and vine crops (melons, cucumbers, winter squash, etc.) are planted last. They prefer weather that is consistently above 55 degrees during the day. Tender vegetables are intolerant of cooler temperatures or cold winds. Balancing the plants’ needs for sufficient warmth with the length of its growing season to reach harvest can be tricky. One suggestion is to look for varieties that have the shortest number of days to harvest on the seed packet. A typical first frost date in our area occurs the first week of October.

Providing optimal growing conditions and care once you have planted your garden produce is provided in CSU Extension Garden Notes #719 on “Vegetable Garden Hints. ” Whether you want to start an asparagus bed, minimize bolting of cole crops or learn the secrets of successful tomato growing and disease prevention, this Garden Notes has the “insider knowledge” to help you harvest home grown veggies bursting with flavor and nutrition!

The author has received training through Colorado State University Extension’s Master Gardener program and is a Master Gardener volunteer for Larimer County

Visit PlantTalk Colorado ™ for fast answers to your gardening questions. PlantTalk is a cooperation between Colorado State University Extension, GreenCo and Denver Botanic Gardens.

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