When to Plant Cannabis Seeds Outdoors
Plant cannabis seeds outdoors after your last spring frost, once the soil has warmed. Hemp research cited by University of Missouri Extension found germination of 80 percent or more between 55 and 80 degrees F soil temperature. Your local frost date from NOAA climate normals and a soil thermometer set the real start date.
When Is It Safe to Plant Weed Seeds Outside?
The safe window opens after the last spring frost has passed and the soil has warmed. Frost can kill a young seedling, and cold, wet soil slows germination. The date changes a lot across the US, so a calendar date from another region is not much help. Start with your local frost data, then check the soil itself. Outdoor growing is not legal everywhere, so check local rules before you plant. Soil quality matters too, and our guide to outdoor soil covers the mix.
What Soil Temperature Do Cannabis Seeds Need?
University of Missouri Extension reports, for hemp, that germination of 80 percent or more occurred between 55 and 80 degrees F soil temperature. It gives an optimal range of 60 to 68 degrees F for northern latitude cultivars and up to 77 degrees F for southern cultivars (University of Missouri Extension). These are hemp field findings, but they give outdoor cannabis growers a sensible range to check against. A soil thermometer at seed depth in the morning shows when your bed is ready.
Hemp germination by soil temperature, University of Missouri Extension
Source: University of Missouri Extension MX73, Missouri Industrial Hemp Production. Hemp findings, not a cannabis germination promise.
| Soil temperature | What MU Extension reports for hemp | Source |
|---|---|---|
| 55 to 80 degrees F | Germination of 80 percent or greater | MU Extension MX73 |
| 60 to 68 degrees F | Optimal for northern latitude cultivars | MU Extension MX73 |
| Up to 77 degrees F | Optimal upper end for southern cultivars | MU Extension MX73 |
How Do You Find Your Last Frost Date?
NOAA’s National Centers for Environmental Information publish U.S. Climate Normals, which include freeze and frost data by weather station (NOAA NCEI). Pick the station nearest you and look up the typical last spring freeze. Treat it as an average, not a promise, because a late cold snap can still come. Our guide to protecting seedlings from cold snaps covers what to do if one is forecast after you plant.
Should You Start Seeds Indoors First?
Many growers do. Starting indoors gives seedlings a head start while the outdoor soil warms, and lets you plant out stronger plants after the frost date. Plants raised indoors need time to adjust to sun and wind, which our guide to hardening off seedlings explains. Direct sowing works too, as long as you wait for warm soil, and our guide to germinating cannabis seeds covers both starts.
Choosing seeds for an outdoor run? See our regular seeds and feminized seeds.
Sources
Some sources below studied hemp or other crops rather than drug-type cannabis. Their findings are reported as results for those crops or settings.
- University of Missouri Extension MX73: Missouri Industrial Hemp Production (PDF)
- NOAA NCEI: U.S. Climate Normals
- Oregon State University Extension EM 9239: Soil, Seedbed Preparation and Seeding for Hemp in Oregon (PDF)
Hemp extension data and NOAA frost normals are the sources for these planting dates, general information from Kind Seed Co for outdoor growers.
FAQ
Can cannabis seedlings survive a frost?
Young seedlings are soft and can be badly damaged or killed by frost, so it is safer to plant after your last frost date. If a cold night is forecast after planting, cover or move young plants. Our cold snap guide covers simple ways to protect seeds, seedlings and young plants from sudden temperature drops.
Is it too late to plant cannabis seeds in June?
It depends on your first fall frost and latitude. Photoperiod plants start flowering as days shorten, so a late start leaves less time to grow before flowering. What matters most is whether the plant can finish before your first fall frost. Check your local frost data and choose seeds whose listed flowering time fits the weeks you have left.
Do autoflowers have a different planting window?
Autoflowers are bred to flower without waiting for shorter days. They still need warm soil to start well and frost-free weeks to finish, so check the listed seed to harvest time against your local frost dates.
How deep should outdoor seeds be planted?
Oregon State Extension reports that industrial hemp is typically seeded 0.5 to 1 inch deep, deeper in dry conditions, and that seeding deeper than 1.5 inches gives progressively poorer emergence. That is a hemp field figure, but it is a useful guide for outdoor cannabis seeds sown straight into soil.
