University of Missouri Extension

Chuck Adamson
Senior Information Specialist
573-882-6843
adamsoncw@missouri.edu

Published: April 3, 2006
Story Source: Mary Kroening, (573) 882-9633, Pat Guinan, (573) 882-5908, Lewis Jett, (573) 884-3287

Planting calendars vary by plant
and region, mid-May usually safe

COLUMBIA, Mo. – While some types of flower and vegetable seedlings can be planted outdoors as early as March or April, many are best left indoors until mid-May.

Mary Kroening, MU Extension Master Gardener program coordinator, recommends Mother’s Day weekend as a safe time to transplant flowers prone to frost injury.

Some popular plants that are susceptible to cold injury include elephant ears, cannas, caladium, coleus, geranium and impatiens.

“Just because they are available to purchase at the nursery does not mean that our weather is conducive to planting,” Kroening said. “Nurseries will start carrying everything in early April. If you start buying things now, keep them in the containers they came in and be prepared to bring them indoors when nighttime temperatures dip below 40 degrees.”

That allows the plants, which likely came from heated greenhouses, to gradually adjust before being transplanted into cooler, outdoor soils.

Some flowers, like pansies and snapdragons, are more tolerant to cold and can be planted in late-March and early-April, Kroening said.

For vegetable planting recommendations, MU Extension has a Web-based planting calendar with suggested varieties. The website is maintained by Lewis Jett, state vegetable crop specialist.

“It’s very important to plant vegetables on time, since most perform best in either cooler or warmer weather,” Jett said. “For example, cool season crops, such as lettuce and broccoli, rapidly lose quality the later they’re planted in the spring. Many pests become increasingly more severe as temperatures increase.”

Lettuce seed and potatoes can go in the ground as early as March in southern and central Missouri and in early April for northern parts of the state, Jett said.

Wait until the last week of April to plant cucumbers in southern Missouri or until mid- to late-May if you’re located in northern Missouri.

Tomato, pumpkin and zucchini plants shouldn’t go into the ground until early- to late-May, depending on your region.

For Jett’s complete vegetable planting guide, go to http://extension.missouri.edu/explorepdf/agguides/hort/g06201.pdf.

A reference point used by many gardeners is the so-called “average frost-free date” – that is, the day in spring when there’s no more than a 50 percent chance that there will be another day of freezing temperatures.

April 15 is the often-cited Missouri average frost-free date, but it varies by region and terrain, said Pat Guinan, MU Extension climatologist. Bootheel areas typically have an average frost-free date of April 5. In northern parts of the state it’s April 20.

Last year, freezing temperatures happened well after the average dates.

“We went three to four days in a row, in the first week of May, with temperatures below freezing in northern parts of Missouri,” Guinan said.

He suggested gardeners go to http://agebb.missouri.edu/weather/frost.htm to look up average frost-free dates by region. Then, as planting times approaches, check the latest temperature forecasts and extended outlooks to decide whether it is safe to plant. The extended six- to 10-day outlooks are updated daily at http://www.cpc.ncep.noaa.gov/products/predictions/610day

For more planting information from MU Extension, log on to http://extension.missouri.edu.

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