Knowing when you should plant hemp seeds into an outdoor field at the right time — not too early and not too late — is an essential factor in a successful hemp harvest.
Plant your tender young hemp seedlings too early and they may be so stressed by cold weather they never get a good start. But plant them out too late and you could easily miss the narrow window appropriate for a quality harvest.
To figure out when to transplant your high cannabinoid hemp seedlings, Colorado Breeders Depot advises hemp farmers to consider four things.
The Ideal Temperature for Transplanting (and Hardening Off Tips) High Cannabinoid Hemp Seedlings
The ideal temperature for planting young hemp seedlings into your field is when spring temperatures have stabilized and your soil temperature is 50 degrees or more.
Use a soil thermometer to get an accurate read on your soil temperatures. Remember, just because your air temperature is more than 50 degrees doesn’t mean your soil temperature is. Spring soil is cooler than air temperatures and will heat up slowly with warming weather.
Well-started young hemp seedlings are pretty sturdy plants and can tolerate even light frosts. The big trick is getting them used to outdoor temperatures before planting out. Growers call this process (used on all crops transplanted into an outdoor field) “hardening off.”
Hardening off gets young plants used to outdoor conditions slowly for at least a few days (ideally a week) before transplanting. The shock of moving from a protected greenhouse to an unprotected outdoor environment can stress a young plant, delay its initial growth, leave it vulnerable to pests and diseases and (in a worst-case scenario) kill it.
To harden off hemp seedlings, plan to expose them to outdoor conditions for a few hours at a time, increasing daily how much time they are outside. Best-case scenario, you harden off your transplants over a week-long period. But even a few days of hardening off before transplanting are better than none!
Some growers harden off their transplants by moving flats from in their greenhouse to outside every day until transplant time. But, especially in larger operations, that requires a lot of labor. Consider instead constructing a temporary “hardening off” structure in a sheltered spot that greenhouse plastic can easily be partially removed (or removed entirely) and then put back up.
The Ideal Day Length for Transplanting Young Hemp Seedlings
Traditional hemp (Cannabis sativa var. indica) is a short-day “photoperiod” plant and requires the right amount of daylight to trigger flowering. It can depend on the varietal, but most traditional hemp cultivars begin flowering when days begin to shorten — somewhere between less than 13 and 15 hours of daylight.
Photoperiodic hemp is easily adaptable for growers in the northern hemisphere that experience lengthening daylight hours in the spring until they begin to shorten after the summer solstice. Young seedlings transplanted in mid-April through May when conditions are warm enough will put on vigorous vegetative growth until sometime in late summer when nights begin to take over days and flowering is triggered. However, if a grower in the north waits to long to transplant out their seedlings, their plants won’t have enough time to put on adequate vegetative growth before flowering is triggered.
Daylight sensitivity gets even trickier for growers in southern latitudes without such extremes between night and day length. Summer solstice in Florida, for example, has not quite 14 hours of daylight (versus in Seattle, summer solstice stretches for 16 hours).
Hemp growers in Florida planting photoperiod varietals that thrive in northern latitudes have a narrow window of just a few weeks around summer solstice to plant — unless they choose hemp seeds bred for their specific daylight requirements.
What Hemp Cultivars You Plant Dictate Your Transplant Date
As the demand for hemp has taken off, hemp breeders like Colorado Breeders Depot recognized the challenges of short-day requirements for hemp farmers in southern latitudes.
Hemp breeders began selecting cultivars more appropriate for locations with less extremes between day versus night-time hours. Every year, many more hemp seed options are available for southern growers, including “autoflowering” hemp.
Autoflowering hemp (Cannabis ruderalis) is a different species of cannabis found growing wild in very northern latitudes where warm-weather conditions are brief. Because of that, ruderalis species naturally developed without daylight sensitivity.
True autoflower hemp varietals are short, small plants with much less flower production than Cannabis sativa/indica varietal, but they do go into flower production as early as 60 days after transplanting (verses 100 to 120 days for traditional hemp).
Autoflowering hemp can be useful for growers in southern latitudes — especially those close to the equator. Or, they can be used by growers with naturally long, mild summers to plant multiple (even as many as three) hemp crop rotations rather than just one. However, they do have challenges, including susceptibility to mold and mildew and much lower cannabinoid production. Make sure to talk with a trusted adviser before planting out autoflowering hemp.
Consider Your Typical Harvest-Time Weather Before Planting
The last element to consider before dialing in your ideal transplanting time is what your typical harvest weather looks like. Outgrown hemp of really any type is best harvested when the weather is dry and not yet too cold.
Suppose your region typically has six weeks of mild, sunny fall weather with nights not traditionally too cold. In that case, you have plenty of flexibility with a long harvest period. If, on the other hand, your summers end abruptly with a monsoon of wet and humid conditions or an arctic blast of cold air, you’ll need to plan accordingly. Plant your transplants out soon enough that they have adequate time to grow and flower before your winter weather sets in.
Of course, transplant time requirements change if you grow out your hemp crop in the controlled conditions of a greenhouse (where even light can be supplemented), as many smokable hemp growers do. But that’s a topic for another blog post! You should also be aware of some government resources that do exist that can help you network with other hemp growers as well.
Are you looking for more information on the right transplant day for your hemp seedlings? Don’t hesitate, give Colorado Breeders Depot a call. We’d love to help you out. We’ll help you consider your opportunities, consult on your grow plan and advise you throughout. Helping our customers have an excellent hemp harvest — starting with the seed they plant — is our number one goal.