Cool Season Vegetables
These vegetables prefer cool growing temperatures (60°F to 80°F) and lose quality in hot weather. Because cool-season vegetables prefer cool growing temperatures, they are often planted in early spring and replanted mid-summer for fall harvest.
Hardy Vegetables
- Crops: broccoli, cabbage, kohlrabi, onions, lettuce, peas, radish, spinach, turnips
- Temperatures: Hardy vegetables grow with daytime temperatures as low as 40°F and may survive a frosty nip.
- When to plant:
- Based on soil temperatures, refer to Table 1.
- As soon as soil adequately dries in the spring.
- As early as 2-4 weeks before the date of the average last spring frost.
Semi-Hardy Vegetables
- Crops: beets, carrots, cauliflower, parsley, parsnips, potatoes, and Swiss chard
- Temperatures: Semi-hardy vegetables grow with minimum daytime temperatures of 40°F to 50°F but are less tolerant of a frosty night.
- When to plant:
- Based on soil temperature, refer to Table 1.
- As soon as soil adequately dries in the spring.
- As early as 0-2 weeks before the date of the average last spring frost.
Table 1. Cool Season Vegetable Planting Guide
| vegetable | Min germination temperature1 | Optimum germination temperature1 | Max germination temperature1 | Plant Spacing2 | Planting Depth | Days to Germination | Typical Days to HarvesT | Age of Transplant (weeks) |
|---|---|---|---|---|---|---|---|---|
| Beets | 40° | 80° | 90° | 4-6” | ¾-1” | 7-10 | 60 | |
| Broccoli3 | 40° | 80° | 90° | 18” | ½” | 3-10 | 65T3 | 5-7 |
| Cabbage3 | 40° | 80° | 90° | 18” | ½” | 3-10 | 85T3 | 5-7 |
| Carrots | 40° | 80° | 90° | 2-3” | ¼” | 10-17 | 70 | |
| Cauliflower3 | 40° | 80° | 90° | 18” | ½” | 3-10 | 5-7 | |
| Kohlrabi3 | 40° | 80° | 90° | 7-9” | ½” | 3-10 | 50 | |
| Leeks | 40° | 80° | 90° | 4-6” | ¼” | 7-12 | 120 | |
| Lettuce (leaf types) | 35° | 70° | 70° | 7-9” | ¼” | 4-10 | 60 | |
| Onions, green | 35° | 80° | 90° | 2-3” | ¼” | 7-12 | 60 | |
| Onion, dry (seed) | 35° | 80° | 90° | 4-6” | ¼” | 7-12 | 110 | |
| Onion, dry (sets) | 35° | 80° | 90° | 4-6” | 1-2” | 7-12 | 110 | |
| Parsnips | 35° | 70° | 90° | 5-6” | ½” | 15-25 | 70 | |
| Peas | 40° | 70° | 70° | 4-6” or 3×8” | 1” | 6-15 | 65 | |
| Potatoes | 45° | 12-15” | 4-6” | 125 | ||||
| Radishes | 40° | 80° | 90° | 2-3” | ½” | 3-10 | 30 | |
| Spinach | 40° | 70° | 70° | 4-6” | ½” | 6-14 | 40 | |
| Swiss Chard | 40° | 85° | 95° | 7-9” | 1” | 7-10 | 60 | |
| Turnips | 40° | 80° | 100° | 4-6” | ½” | 3-10 | 50 |
| 1 Germination temperature – Soil temperature is one of the best methods to determine spring planting time. Plant when soils reach minimum temperature measured at 8 a.m., 4” deep. Beans are an exception, being measured at 6 inches deep. Optimum temperatures listed in the table are useful for starting seeds indoors. Maximum temperatures are listed in regard to high soil temperatures that may interfere with seed germination in the summer. 2 Plant spacing – Spacings given are equal-distance spacing for crops grown in block or close-row style beds. For example, beets, with a spacing of six inches are thinned to six inches between plants in all directions. In other words, beets are thinned to six inches between beets in the row and six inches between rows. The closer spacing listed should be used only on improved soils with 4-5% organic matter. Close-row or block-style planting works well for raised bed gardening, with blocks/beds 2-4 feet wide (any length desired) and 2-foot wide walkways between blocks/beds. 3 Transplanting cole crops – Since cole crops (cabbage, cauliflower, broccoli, and Brussels sprouts) germinate better in warmer soil, they are typically started from transplants in the spring. Days to harvest are from transplants. In the warmer areas of Colorado, these crops produce the best quality when directly seeded mid-summer (early July for the Front Range area) for harvest during cooler fall weather. Before planting out, harden off seedlings. |
Warm Season Vegetables
Warm-season vegetables prefer summer-like weather with temperatures between 70°F and 95°F. They are intolerant of frost and may be sensitive to cool spring winds.
Tender Vegetables
- Crops: beans, celery, corn, cucumbers, New Zealand spinach, summer squash
- Temperatures: Tender vegetables grow with a daytime temperature above 55°F and are intolerant of frost.
- When to plant:
- Based on soil temperature, refer to Table 2.
- Soil is adequately dry to work.
- From seed: around the date of the average last spring frost
- Transplants: cucumbers and summer squash without frost protection should be delayed until frost potential is over.
Very Tender Vegetables
- Crops: lima beans, cantaloupe, eggplant, pepper, pumpkin, winter squash and pumpkins, tomato, and watermelon
- Temperatures: Very tender vegetables are not only intolerant of frost, but also cool spring winds. They need daytime temperatures above 60°F, and prefer temperatures of 70°F to 95°F. A week of daytime temperatures below 55°F may stunt the crop.
- When to plant:
- Based on soil temperature.
- Soil is adequately dry to work.
- Typically 2+ weeks after the average last spring frost date.
- Weather is becoming summer-like, (i.e., consistently above 55°F (daytime) and breezes should have lost any cool nip).
Table 2. Warm Season Vegetable Planting Guide
| vegetable | Min germination temperature1 | Optimum germination temperature1 | Max germination temperature1 | Plant Spacing2 | Planting Depth | Days to Germination | Typical Days to HarvesT | Age of Transplant (weeks) |
|---|---|---|---|---|---|---|---|---|
| Beans, snap | 55° | 80° | 90° | 6” or 4”×12” | 1-1½” | 6-14 | 60 | |
| Cantaloupe3 | 60° | 90° | 100° | 36”-48” | 1-1½” | 3-12 | 85 | 2-33 |
| Corn | 50° | 80° | 100° | 12”×30” or 9”×36” | 1-1½” | 5-10 | 60-90 | |
| Cucumbers3 | 60° | 90° | 100° | 6” trellised, 24-36” untrellised | 1” | 6-10 | 55 | 2-33 |
| Eggplant4 | 60° | 80° | 90° | 18-24” | ¼” | 7-14 | 60T4 | 6-9 |
| Pepper4 | 60° | 80° | 90° | 15-18” | ¼” | 10-20 | 70T4 | 6-8 |
| Tomato4 | 50° | 80° | 100° | 24” trellised | ¼” | 6-14 | 65T4 | 5-7 |
| Squash, Summer3 | 60° | 90° | 100° | 36-48” | 1-1½” | 3-12 | 50 | 2-33 |
| Squash, Winter3 | 60° | 90° | 100° | 36-48” | 1-1½” | 6-10 | 100 | 2-33 |
| Watermelons3 | 60° | 90° | 110° | 36-48” | 1-1½” | 3-12 | 85 | 2-33 |
| 1 Germination temperature – Soil temperature is one of the best methods to determine spring planting time. Plant when soils reach minimum temperature measured at 8 a.m., 4” deep. Beans are an exception, being measured at 6 inches deep. Optimum temperatures listed in the table are useful for starting seeds indoors. Maximum temperatures are listed in regard to high soil temperatures that may interfere with seed germination in the summer. 2 Plant spacing – Spacings given are equal-distance spacing for crops grown in block or close-row style beds. For example, beets, with a spacing of six inches are thinned to six inches between plants in all directions. In other words, beets are thinned to six inches between beets in the row and six inches between rows. The closer spacing listed should be used only on improved soils with 4-5% organic matter. Close-row or block-style planting works well for raised bed gardening, with blocks/beds 2-4 feet wide (any length desired) and 2-foot wide walkways between blocks/beds. 3 Transplanting vine crops – Vine crop (cucumbers, squash, melons) roots are extremely intolerant of being disturbed, and perform best when grown by direct seeding rather than by transplants. With the use of black plastic to warm the soil, directly seeded crops germinate rapidly. If using transplants, select small, young plants, not more than 2-3 weeks from seeding. 4 Tomato family transplants – The tomato family is traditionally planted from transplants purchased or started from seed indoors. In warmer areas of Colorado, they can also be directly seeded with minimal delay. Days to harvest are from transplants. |
This publication, reference GardenNotes #720, is developed as part of the Colorado State University Extension Master Gardener Program.