Suggested Vegetable Planting Dates: Grand and San Juan Counties
Reagan Wytsalucy, USU Extension Assistant Professor, Agriculture – San Juan County
Cory Farnsworth, USU Extension Assistant Professor, Agriculture – Grand County
Dan Drost, USU Extension Emeritus Vegetable Specialist
Introduction to Vegetables
“When should I plant?” and “What should I plant?” are two of the more common questions received from Utah gardeners. To answer the “When” question, you need to know something about the climate where you live. Vegetable plants vary in their response to temperature and are grouped by how they cope with cold or hot conditions. There are four (4) vegetable groups (Maynard, 2006), which include the hardy, half-hardy, tender, or very tender crops. These groups are also referred to as the cool-season (hardy or half-hardy) and warm-season (tender or very tender) vegetables (see Tables 2 and 3).
Cool-Season Vegetables
Cool-season vegetables like moderate temperatures (range 40 °F to 80 °F), and many can survive frost events. Seeds germinate at cooler soil temperatures, plants are typically smaller, many are biennials, and the plant parts eaten are roots, stems, leaves, and immature flower parts. The hardy vegetables can withstand colder conditions and are often planted sooner than the half-hardy vegetables.
Warm-Season Vegetables
Warm season vegetables like warmer temperatures (range 55 °F to 90 °F), grow poorly or are damaged by temperatures between 32 °F to 50 °F, and do not survive frost events. Seeds germinate at warm soil temperatures (+60 °F), plants are large, and the plant parts eaten are immature and mature fruits. The tender crops grow well at lower warm temperatures and are planted sooner than the very tender vegetables.
Local Weather Affects Planting Decisions
To decide “When to plant,” you need to consider the vegetable being grown and the unique weather conditions where you live. Since weather conditions vary greatly (day-to-day, year-to-year), climate scientists gather long-term weather observations to identify average conditions for a location. Gardeners and growers can use this information to help make planting decisions (“When to plant”) and determine if there is enough time to grow the crop of choice (“What to plant”).
Considering Local Climate
Utah’s climate is variable due to its mountains, valleys, deserts, canyons, and elevations. Having local information on climate conditions becomes important because weather is local. In this publication, we use the average last spring frost and average first fall frost to identify suggested planting dates and length of the growing season for some cities and towns in Utah. For more details about weather conditions in your city or town, visit the Utah State University (USU) Utah Climate Center website. Not all cities or towns have weather station data, and some sites may no longer collect weather data. The data is free, represents what the weather was like in the past, and does not predict future weather events.
Choosing Plants
Deciding “What to plant” is personal. Choices include cool-season vegetables like broccoli, carrot, radish, or onion. Cool-season crops are planted weeks before the average last spring frost and up to or after that date. Planting a cool-season crop too late risks exposing it to warmer temperatures than it likes and can cause some to flower prematurely (or bolt). This will reduce plant growth and yield. Warm-season vegetables like cucumber, pepper, and tomato should be planted near or after the average last spring frost Planting a warmseason crop too early risks exposure to cooler temperatures than it likes. In addition, if planted too late, there may not be sufficient time for the crop to mature. Planting too early or too late will reduce plant growth and yield.
Using Seeds or Transplants
Gardeners can start crops from seed or transplants (young plants). Seeds often take longer to mature than transplants. In areas with very short frost-free periods, it may be better to use transplants Regardless of where you live, pay attention to the frost-free period as this helps you determine if there is enough time during the growing season to get the warm- or cool-season vegetable of choice time to mature. For details on growing transplants, look at these USU Extension resources:
• Publication: Vegetable Transplant Production (Drost, 2015) provides information on growing healthy, compact, well-rooted transplants.
• Book: Vegetables, Fruits, & Herbs Book (2012) provides instructions on how to grow many different vegetables
• Website: Yard and Garden provides the latest up-to-date detailed information on gardening, soils, and pests, and has detailed growing information for vegetables in Utah.
Use Data for What to Plant and When
Step 1. First, use Table 1 to find local city or town information (near your location). Use this to get an estimate of the average last spring frost or average first fall frost. Not all cities or towns are listed or have recorded weather details. You may need to estimate dates based on proximity to a city or town or consult with a knowledgeable neighbor or experts at your local Cooperative Extension office.
Step 2. Then, use Table 2 or Table 3 to identify the vegetables of interest and their hardiness group. Use these tables to help estimate the safe spring or fall planting dates. Some specific guidelines for when to plant follow.
Hardy Vegetables
For hardy vegetables (Table 2), plant seeds as soon as the soil dries out in the spring and soil temperatures are above 40 °F. Seeds germinate well at cooler soil temperatures. Plants and transplants can tolerate some frost. Transplant outdoors about 4 weeks before the average last spring frost. If plants are protected with row covers, plant covers, or tunnels, you can transplant 6 weeks early. Biennial crops (cabbage, onion, others) may
produce seed stalk when exposed to extended periods of cool weather (<40 °F).
• Direct-seeding: All hardy vegetables can be direct-seeded except garlic, horseradish, and rhubarb (commonly vegetatively propagated)
• Transplanting: Artichoke, asparagus, broccoli, Brussels sprouts, cabbage, horseradish, rhubarb, and spinach are commonly transplanted.
Half-Hardy Vegetables
For half-hardy vegetables (Table 2), plant seeds at least 2 weeks after the hardy vegetable group or about 4 weeks before the average last spring frost. Seeds require slightly warmer soil temperatures (50 °F) for rapid germination. Transplants may show some damage if exposed to freezing temperatures. Transplant 3–4 weeks earlier than the frost date if protected with row covers, plant covers, or tunnels. Biennial crops (beet, carrot, others) may flower if exposed to extended periods of cool weather
• Direct-seeding: All half-hardy vegetables can be grown from seed except potato (tuber pieces).
• Transplanting: Cauliflower, celery, endive, globe artichoke, lettuce, and pak choi (bok choy) can be transplanted.
Tender Vegetables
For tender vegetables (Table 3), seed on or just before the average last spring frost. Seeds require warm soil temperatures (above 60 °F) for rapid germination. Transplants will show damage if exposed to temperatures below 40 °F (chilling injury), and most grow poorly at air temperatures less than 55 °F. Seed or transplant 2 weeks before the last frost date if protected with row covers, plant covers, or tunnels. Generally, tender vegetables are only spring-planted.
• Direct-seeding: All tender vegetables can be grown from seed.
• Transplanting: Tomato is commonly transplanted.
Very Tender Vegetables
For very tender vegetables (Table 3), seed on or 1–2 weeks after the average date of the last spring frost. Seeds require warm soil temperatures (above 65 °F) for rapid germination. Transplants will be damaged if exposed to temperatures below 45 °F (chilling injury) and most grow poorly at air temperatures less than 60 °F. Seed or transplant 1–2 weeks before the last frost date if protected with row covers, plant covers, or tunnels. Generally, very tender vegetables are only spring-planted.
• Direct-seeding: All very tender vegetables can be grown from seed (except sweet potato), provided the frost-free period is longer than 125 days.
• Transplanting: Use transplants (except lima bean and peanut) in areas where the frost-free period is short or when earlier production is desired.
Late Summer or Fall Production
Many hardy and half-hardy vegetables can be planted for a fall harvest (Table 2) Select short-maturity cultivars and either direct-seed or transplant the crops. For later fall plantings, transplants are recommended, and some plant protection (row covers or frost blankets) may be required. If you have a high tunnel, many hardy and half-hardy vegetables can be grown well into the winter. Time seeding or transplanting relative to the average fall frost date (Table 1). Commonly, you need to plant seeds 4–6 weeks before the average fall frost Pay
attention to the days to maturity information written on the seed packet. Use that information to help determine if there is enough time for the crop to mature. When transplanting into the garden, transplants should be 4–6 weeks old (3–6 leaf stage) and then planted 4–6 weeks before the average fall frost date when grown outdoors. Finding transplants for fall planting may be difficult, so you may need to grow your own plants. If planting under row covers, low tunnels, or in high tunnels, seeding and transplanting dates should be 1–2 weeks before the average fall frost date. In most locations, fall planting of tender vegetables is not recommended.
Notes. Frost/freeze events can vary over short distances due to changes in elevation and topography. The historical averages come from long-term records gathered around Utah by the Utah Climate Center. These averages are only illustrative and may not accurately reflect conditions in all areas or locations. Average frost dates in other cities or towns may be available by searching their records. When local data is not available, your local county Extension office can help estimate these dates. Tracking weather data (garden weather stations) for your own garden can help estimate when to plant.
Table 2. Suggested Spring and Fall Planting Times for Cool-Season (Hardy or Half-Hardy) Vegetables, Which Need Temperatures Warmer Than 35 °F to 40 °F for Good Growth and Can Withstand Light Frosts if Protected
Table 3. Suggested Planting Times for Warm-Season (Tender or Very Tender) Vegetables, Which Grow Best at Temperatures Warmer Than 50 °F to 60 °F and Can Be Planted Early if Protected From Cold
Photo Credit
USU Extension provided all images.
References
Drost, D. (2015). Vegetable transplant production [Fact sheet]. Utah State University Extension. https://digitalcommons.usu.edu/extension_curall/704/.
Maynard, D. N. & Hochmuth, G. J. (2006). Knott’s handbook for vegetable growers (5th ed.). John Wiley & Sons, Inc.
Moller, A. L. & Gillies, R. R. (2008). Utah climate (2nd ed.). Utah Climate Center, Utah State University. Utah State University Extension. (n.d.). Yard and garden. https://extension.usu.edu/yardandgarden/
Utah State University Extension. (2012). Vegetables, fruits & herbs book: A guide to vegetables, fruits & herbs.
https://usuextensionstore.com/vegetables-fruits-and-herbs/
Utah State University Extension. (2021). Fruit, vegetable, and herb growing guides. Yard and Garden.
https://extension.usu.edu/yardandgarden/fruits-vegetables-herbs.
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January 2024
Utah State University Extension
Peer-Reviewed Fact Sheet
Suggested citation: Wytsalucy, R., Farnsworth, C., & Drost, D. (2024). Suggested vegetable planting dates: Grand and San Juan counties [Fact sheet]. Utah State University Extension.