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FROM THE GROUND UP | LINN COUNTY MASTER GARDENERS

Time is right for cool season flowers, vegetables

Designer viola mixes like this Sorbet Ocean Breeze will make you look like a cool season landscape professional. (MCT)
Designer viola mixes like this Sorbet Ocean Breeze will make you look like a cool season landscape professional. (MCT)

Spring has sprung and gardeners of all kinds and ages are eager to start digging in the dirt. However, the cool weather has delayed much garden work.

Vegetable seeds and seedlings require a minimum soil temperature to germinate and grow. Optimal soil temperatures are required for them to thrive. The soil temperature triggers seed germination and the release of minerals in the soil for vegetable growth. The optimal soil temperature for planting and growing most vegetables is 65 to 75 degrees. Linn County soil temperature on April 14 was 42 degrees.

You also can test for soil workability. Simply squeeze a handful of soil in the palm of your hand; if the soil remains a wet clump, it is not workable. Let the soil dry until that handful of soil crumbles from your hand with a touch. It is then ready for spring planting.

Vegetables

Vegetables are identified as either cool season or warm season. Cool season plants are those that can withstand colder temperatures and are the first ones to be planted in the spring, typically as soon as the ground can be worked. Mid-April on are common planting times for these vegetables, always depending upon weather conditions.

Planting can typically begin once the soil temperature reaches 45 degrees and the soil passes the workability test.

Common cool season vegetables include lettuce, spinach, radish, onions, cabbage, kale, brussels sprouts, beets and peas. Most of these vegetables are grown directly from seed and need to be planted early enough in spring to complete their full growth cycle before temperatures get too hot. Hot weather quickly deteriorates quality and causes bolting or unpleasant taste to occur.

Warm season vegetables require higher soil and air temperatures to grow and prevent damage. They are planted after the last frost date — in our area considered to be around mid-May. Typical warm season vegetables include tomatoes, peppers, squash, beans, cucumber, eggplant, corn and sweet potatoes. Many of our warm-season vegetables are started from seed indoors and then transplanted into the garden, as the growing season may be too short to allow them to grow from seed directly in the garden.

For those gardeners who just can’t wait or when the weather turns colder than usual, one might consider using row covers. Row covers help the soil warm quicker in the spring for seed germination and also protect some of the more tender plants from those extra cold nights.

Flowers

Not a vegetable gardener? There are also cool season and warm season flowers.

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Cool season annuals thrive in colder weather, even when nighttime temperatures hit freezing. Most require plenty of moisture but not soggy soil. When daytime temperatures regularly get to 80 degrees or above, these annuals start to brown, flowers shrivel and blooming stops.

Common cool season annuals that include pansies, snapdragons, and sweet alyssum are easiest grown from starter plants. Poppy, larkspur, violas and bachelor buttons are cool season annuals that can be scattered on the ground, often in March or April in Iowa, as soon as the snow melts.

Warm season annuals include favorites such as impatiens, marigolds, petunias, geraniums, salvia, celosia and zinnias. Frost kills them, and planting too early in wet, cold soil inhibits growth and invites pests and disease to enter their world. These are planted outside after the danger of frost has passed.

Perennials are those plants that return year after year. Many are already popping up in the gardens. These can typically be planted anytime the soil becomes workable, which can be anytime between March and May in our area.

For further information about planting your vegetable or flower garden, Iowa State University Extension Store has a vast array of brochures, most of which can be downloaded for free. That website is www.extension.iastate.edu. Then click on “browse store” and you will find much valuable gardening information.

• For gardening questions, call the Linn County Extension Master Gardener Hortline at (319) 447-0647.

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