Did you know if you sow seeds at certain soil temperatures you will get the best germination rates? Every plant species has its own sweet spot, and the more we accommodate this, the better the results. Start measuring your soil temperature to know the best time to sow seeds.
For more beginner tips, also see Seed Starting 101 and clever ways gardeners use warmth to speed up seed germination. This lists best soil temperatures for flowers and herbs.
Using Soil Temperatures For Better Germination
This is one of the best kept secrets in gardening. Each type of seed has a sweet spot—a preferred soil temperature—where germination is most successful. If conditions including temperature are right, you get maximum germination rates and faster growth.
When growing vegetables, the closer we are to best soil temperatures for germination, the more plants we will have.
I’ve provided a chart listing the best soil temperature for each vegetable, suggestions to simplify your sowing, and growing tips including how to measure soil temperature.
There is also a printable chart in the Resources section.
Contents
- Vegetable Seed Sowing Soil Temperature Chart
- Simple Sowing Options
- Why Soil Temperature Matters
- How to Measure Soil Temperature
- Frequently Asked Questions
- Resources
Vegetable Soil Temperature Sowing Chart
This chart is generalized based on hours of research. I could not always find a consensus for optimum temperatures so I’ve listed ranges that should be accurate within a few degrees.
Most of this information comes from studies and growers with much more controlled environments than we have in our gardens. But the ranges can give us a general idea of what plants seem to like.
Always read your seed packets for specific sowing tips. Even within one species there are often exceptions for specific varieties.
As mentioned, there is a printable version available in the Resources section.
| Plants | Soil Temperature | Plants Per Square Foot | Days to Maturity |
|---|---|---|---|
| Asparagus | 75°F (24°C) | 1 | Harvest annually |
| Arugula | 40-53°F (4-12°C) | Open spaces | 30-50 days |
| Basil | 70°F (21°C) | 4 | 30-45 days |
| Beans, Broad | 50-70°F (10-21°C) | 8 | 75-100 days |
| Beans, Bush + Pole | 70-90°F (21-32°C) | 8 | 50-100 days |
| Beans, Runner | 70-90°F (21-32°C) | 8 | 75 days |
| Beans, Soya | 70-90°F (21-32°C) | 9 | 78-85 days |
| Beets | 50-80°F (10-26°C) | 9-16 | 50-70 days |
| Broccoli | 50-85°F (10-30°C) | 1 | 48-100 |
| Broccoli, sprouting | 50-85°F (10-30°C) | 1 | 75-120 days |
| Brussels Sprouts | 50-85°F (10-30°C) | 1 | 100-120 days |
| Cabbage | 50-85°F (10-30°C) | 1 | 45-120 days |
| Carrots | 45-85°F (7-30°C) | 16 | 55-130 days |
| Cauliflower | 50-85°F (10-30°C) | 1 | 60-270 days |
| Celery | 60-75°F (15-24°C) | 4 | 45-110 days |
| Celeriac | 60-75°F (15-24°C) | 4 | 110 days |
| Chickpeas | 50°F (10°C) | 4 | 90-100 days |
| Chicory | 50-72°F (10-22°C) | 1 | 70-90 days |
| Chives | 70-75°F (21-25°C) | 16 | ongoing |
| Cilantro | 55-68°F (13-20°C) | 1 | 45 days |
| Claytonia | 50-72°F (10-22°C) | Open spaces | 55 days |
| Collards | 50-85°F (10-30°C) | 1 | 50-80 days |
| Corn | 60-70°F (15-21°C) | 4 | 70-110 days |
| Corn Salad | 45-65°F (5-18°C) | Open spaces | 30-50 days |
| Cress | 50-72°F (10-22°C) | Open spaces | 10-50 days |
| Cucamelon | 60-85°F (15-30°C) | 2 | 67 days |
| Cucumbers | 60-85°F (15-30°C) | 2 | 45-70 days |
| Eggplant | 75-90°F (24-32°C) | 1 | 58-90 days |
| Endive Radicchio | 50-72°F (10-22°C) | 4-8 | 85 days |
| Garlic | Plant in fall | 9 | midsummer harvest |
| Kale | 50-85°F (10-30°C) | 2 | 40-80 days |
| Kohlrabi | 50-85°F (10-30°C) | 9 | 55-70 days |
| Leeks | 50-75°F (10-25°C) | 9 | 65-135 days |
| Lettuce | 50-72°F (10-22°C) | 4 | 35-80 days |
| Mesclun Mix | 50-72°F (10-22°C) | Open spaces | 30 days |
| Mustard | 70°F (21°C) | 12 | 35-80 days |
| Okra | 75-90°F (24-32°C) | 1 | 56 days |
| Onions & Scallions | 70-75°F (21-25°C) | 9-16 | 50-180 days |
| Pac Choi | 50-85°F (10-30°C) | Open spaces | 30-60 days |
| Parsley | 85°F (29°C) | 6-8 | 70-90 days |
| Parsnips | 50-75°F (10-25°C) | 4 | 110-150 days |
| Peas | 50-70°F (10-20°C) | 8 | 55-85 days |
| Peppers | 64-75°F (18-24°C) | 1 | 60-120 days |
| Potato | 65-80°F (15-27°C) | 4 | 110 days |
| Pumpkin | 90°F (32°C) | 1 vertically | 80-130 days |
| Purslane | 50-72°F (10-22°C) | Open spaces | 60 days |
| Quinoa | 65-75°F (18-24°C) | Check seed packet | 100 days |
| Radish | 65-75°F (18-24°C) | 16 | 24-120 days |
| Rhubarb | 60-75°F (16-25°C) | 1 | 12-18 months |
| Rutabaga | 65-70°F (18-21°C) | 4 | 90-100 days |
| Spinach | 45-70°F (5-20°C) | 9 | 30-50 days |
| Squash | 68-95°F (25-35°C) | 1-2 vertically | 70-115 days |
| Swiss Chard | 50-85°F (10-30°C) | 4 | 50-65 days |
| Tomatoes | 68-95°F (25-35°C) | 1 | 50-93 days |
| Turnips | 65-70°F (18-21°C) | 4 | 35-60 days |
| Watermelon | 75-95°F (24-35°C) | 1 vertically | 70-120 days |
| Zucchini | 68-95°F (25-35°C) | 1-2 vertically | 50-100 days |
Simple Sowing Options
It’s unrealistic to think we’re going to time our seed sowing to suit each and every preferred soil temperature—although the chart is handy if you’re just sowing a few.
To simplify sowing, I suggest organizing your crops into warm and cool groupings. This is a realistic way to get your crops germinating as fast as possible while allowing enough time for the plants to mature during the growing season.
Warm Crops
Mainly Tender Summer Crops
Approximate Seed Sowing Soil Temperature Range:
68-79°F | 20 -26°C
Basil
Bean
Cabbage*
Cilantro/ coriander
Corn
Cucumber
Dill
Eggplant
Melons
Mustard
Nasturtium
Okra
Onion
Peppers
Pole bean
Pumpkin
Sage
Squash – Summer + Winter
Sweet potato
Tomato
Watermelon
Zucchini
Cool & Cold Crops
Spring and Autumn Crops
These crops do best during spring and fall when outdoor temperatures are cooler although some of them like a warmer start for the seeds (see the chart).
You can grow them in summer—and we do—but there’s always the risk of bolting (skipping right to the seed production stage) in excessive heat.
I start my cool fall crops indoors in mid-summer for planting outdoors at the end of summer.
Many of these crops can be over-wintered in cold frames.
This explains when it’s safe to plant or sow outdoors in spring before last frost and this has more tips on direct sowing before last frost.
Approximate Seed Sowing Soil Temperature Range:
50-68°F | 10-20°C
Asparagus
Beet
Broad bean
Broccoli
Broccoli raab
Brussels sprouts
Cabbage*
Carrot
Cauliflower
Celery
Celeriac
Chervil
Chives
Claytonia
Collards
Endive
Garlic
Kale
Kohlrabi
Leafy greens
Leek
Lettuce
Mache
Mibuna
Mizuna
Mustard
Onion
Pak choi
Parsley
Parsnip
Pea
Potato
Radish*
Rosemary
Rutabaga
Sage
Salad greens
Scallion
Spinach
Swiss Chard
Tatsoi
Thyme
Turnip*
*Cabbage, radish, and turnip are considered cool crops but do like extra warmth for seed germination.
Why Temperature Matters
What is a seed?
Seeds contain embryonic tissue and food stores that nourish early growth, enclosed in a protective coat. That coat prevents germination (growth) until conditions including moisture and temperature change.
Seed Storage
To store seeds and prevent germination, it is recommended to keep them in a cool, dry, dark place with consistent temperatures between 32-41°F (0-5°C) and not more than 50% relative humidity levels.
- Best Ways to Store Seeds at Home (Fridge & Other Options)
- How Seeds Are Kept in Long-Term Storage (Global Seed Vault)
Seed Germination
To awaken seeds from dormancy and trigger germination, conditions must change. When we sow a seed, we introduce water (moisture), which softens the protective coat, and warmer temperatures which provoke growth. Air and light play a role as well.
When we look at temperatures for seed germination, it is the temperature of the soil or growing medium in direct contact with the seed or roots that is so important. Research shows that every single plant species has its own preferences. Getting the soil temperature right—or within optimum range—can greatly affect germination rates.
Example
- Ten pepper seeds started at 60°F (15°C) may yield one or two plants, and take weeks to sprout.
- The same number of seeds started at 85°F (29°C) may sprout within days and yield 8-10 happy plants.
- But, beyond that temperature, the seeds may not survive.
This is what we refer to as a seed liking “warm feet.” Keep in mind that this is just one example and the sweet spot is different for each plant species (and can vary by subspecies as well).
How to Measure Soil Temperature
Tip: Check Your Soil Temperature
In spring, pay attention to night-time low temperatures, not day-time highs. When the lows are consistently above 50°F or 10°C, the soil becomes warm enough for some seed sowing.
- For a good temperature reading, place the thermometer in the soil approximately 3″ deep (or however deep the tip allows) and allow a minute for a definite reading.
- Measure both in the morning and afternoon, a few days in a row.
- The process is the same for indoor seed starting. Take enough readings that you are confident the soil is consistently within the desired temperature range.
- Note all the readings and take the average. When the average is in range, it’s sowing time—assuming it’s the right time of year.
Thermometers
You can use a kitchen meat thermometer to measure soil temperature or get an official soil thermometer, which is really the same thing. I have a digital thermometer with a metal probe and it works nicely.
Tips For Warming Soil in Spring
For outdoor sowing, one practical way to increase soil temperature is to add a few inches of compost to the soil. Some gardeners also place a temporary cover like thick, black plastic over the planting area. This will help keep warmth in and expedite the temperature gain.
Indoors, you can use a seedling heat mat to warm the soil for better and faster seed germination rates if your seed sowing area is unusually chilly (mid 60s°F | 15°C or cooler). This explains when a heat mat can help.
I also have a list here of clever ways gardeners use existing warmth within their homes to help speed up germination.
Frequently Asked Questions
The best soil temperature for planting vegetables depends on the species and variety you are growing. To keep it simple, divide your seeds into two groups: warm crops and cool crops. Generally, warm crops like tomatoes germinate best in soil temperatures of 68-79°F (20 -26°C). Cool crops like leafy greens prefer 50-68°F (10-20°C).
Soil temperature can be measured using any household or kitchen thermometer. A digital thermometer with a probe makes it easy to get an instant reading at various soil depths including the depth you will sow the seeds and the future root depth.
To time vegetable seed sowing right, first ensure your timing is right to allow the plant the necessary time to mature within your growing season. Next, start checking your prepared sowing area and take soil temperature readings. Take several readings at different times of day and night over several days and sow when the average is within the desired temperature range.
Most seeds need both moisture and warmth to sprout. Once a seed starts germinating, it cannot dry out or germination will end. When sowing vegetable seeds, ensure you maintain consistent moisture within the optimum soil temperature range for that species and variety.
Carrot seeds can germinate in soil temperatures ranging from 45-85°F (7-30°C). Always check your seed packet for specific recommendations for the seeds you are sowing.
Tomato seeds germinate best in soil temperatures ranging from 68-95°F (25-35°C). Tomato plants grow best in the middle of this range. If air and soil temperature is too cold, growth stalls. If air and soil temperature is too warm, the flowers may wither and die instead of producing fruit.
Resources
Free Printable
If you would like to save the soil temperature chart, click on button (below).
New to saving files? There are step-by-step instructions here.
Empress of Dirt
FREE TIP SHEET
Best Soil Temperatures For Sowing Vegetables
This file includes a chart showing the optimum soil temperatures for sowing common vegetables.
The download link will be sent to your email.
Joining our free newsletter list is optional at checkout.
Flowers & Herbs
This has a soil temperature chart for sowing popular flower and herb seeds.
Like vegetable seeds, these plants also have preferred soil temperature ranges for germination.
Mail Order Seeds
- SeedsNow | Botanical Interests United States
- West Coast Seeds Canada
If you are eager to sow seeds in spring or fall, check the cool crop list for candidates, and grab your thermometer. Start checking your soil temperature and sow when conditions are right.
Warm crops can often be slow-growers and do best with indoor seed starting to allow enough time for the plant to mature and fruit.
~Melissa the Empress of Dirt ♛