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I Didn’t Know That!

By Heide Dolan, Colorado Master Gardener

Seed Starting

Lettuces, kale and snap peas started outside under cover, Photo: Heide Dolan

Fresh veggies straight from your garden…a gardener’s dream! For veggie seed sowing success, arm yourself ahead of time with knowledge. Different vegetable varieties need different soil temperatures for their seeds to germinate properly. This temperature information guides both when and where you sow your seeds. Seed packages list this information so read them carefully.

Cool season crops include broccoli, some lettuces, kale, peas and radishes. These crops will germinate with cooler soil temperatures, as low as 40°, but optimal germination usually occurs at 70° to 80°. Rather than direct sowing in the garden, some people prefer to start plants by sowing indoors on a heat mat. When the plants are four to eight weeks old and outside soil is warmer, move the plant starts to the garden. Some seeds don’t transplant well, such as carrot, radish and cucumber. Sow these directly into the garden when the soil is warm enough.

Microdwarf tomato seedlings thriving under lights, Photo: Heide Dolan

Tomatoes and peppers are warm season crops. Optimum soil temperatures for these plants are 80° to 90°. Because tomatoes and peppers take a longer time to grow and fruit than our short Colorado growing season provides, start these plants from seed indoors on heat mats or in sunny windows eight weeks before you plan to move them to the garden.

Peppers started indoors on heat mats, Photo: Heide Dolan

A soil thermometer is your friend when direct sowing seeds in Colorado. These tools are inexpensive, and help you accurately assess soil temperature. It’s fun to get your thermometer out and test different garden spots. Ground soil is much colder than raised bed soil. Container soils warm more quickly, enabling you to sow earlier. The sizes of containers and direct sun exposure will affect these temperatures.

For more information on germination temperature requirements of both cool and warm season veggies, please see this link.

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