10 Steps to Growing Sensational Cannabis Seedlings
March 16, 2023 
Cannabis seedlings starting to emerge. Photo: Ryan Douglas
With spring fast approaching, many cannabis cultivators will be sowing seeds to get a jump start on the growing season. Those precious weeks between seed germination and planting out or potting up are critical to ensuring a healthy and efficient crop.
Oversights during this production stage can have expensive ramifications for a cannabis cultivation business. Weak, spindly cannabis seedlings are more prone to crop problems and cost much more to grow than strong, stalky seedlings.
Start the growing season off right with these 10 tips for producing sensational cannabis seedlings.
#1: Start With Healthy Seeds
Cannabis seeds come in various sizes and colors, and it’s impossible to guess which are the most viable. Small, white, or green seeds sometimes germinate, but if you have the luxury of selecting from a sizable lot, go for dark, plump seeds with distinct “tiger stripes.” They won’t disappoint.
#2: Select a Germination Method
There are several ways to germinate cannabis seeds successfully. Home growers often use wet paper towels or individually sow seeds into small pots. Commercial growers typically sow into 50- or 72-count plug trays and place them into germination chambers or under constant mist in a greenhouse. Indoors, growers simply use the same propagation room as they do for rooting cuttings.
#3: Keep Moisture and Temperature On-Point
Cannabis seeds require 100% moisture and warm temperatures to germinate. Aim for 85°F until the seeds crack or emerge from the soil, and then slowly shift to 75°F to 78°F to begin growing. Be cautious when removing germinated seeds from wet paper towels, as they are in the most fragile state of their life cycle. Use tweezers and a gentle hand.
#4: Light ‘em Up
Avoid stretchy seedlings by providing sufficient light as soon as seeds emerge from the soil. Want to play it safe? Illuminate seedling trays a day before you expect them to emerge. Under the right conditions, cannabis seedlings will stretch astonishingly fast in the 15 hours between the time your cultivation staff goes home and when they return the next day. Greet your seedlings with at least 300 to 500 micromoles of light on Day One.
#5: Feed Your Babies
Cannabis seeds contain enough minerals to support tap root initiation and cotyledon growth, but not much else. As soon as the first true leaves appear, start feeding with a complete fertilizer at an EC of .75-1.5. Remember that some peat-lite germination mixes contain a fertilizer pre-charge that provides seedlings with sufficient nutrition for the first week or ten days of growth. Ensure you don’t double up on fertilizer and burn young plants from overfeeding.
#6: Go With the (Air)flow
A stagnant, humid grow room is one of the fastest ways to damage young cannabis seedlings. Humid environments will force seedlings to stretch, causing a myriad of production problems. Soft plant tissue at the base of the stem becomes ultra-susceptible to bacterial and fungal attacks and can result in seedlings falling over or damping off. Even if they survive, they’ll require extra labor and support throughout the vegetative growth stage. Prevent these headaches by maintaining relative humidity at 70% to 80% with gentle, non-direct airflow.
#7: Provide Some Elbow Room
As soon as cannabis plants detect other leaves around them, they’ll shift their growth from “out” to “up.” Plants will quickly grow vertically to find more space to continue expanding outwards. This upward race results in the same negative ramifications as stretch caused by low light or high humidity. 50-cell plug trays work well, providing plants sufficient time to develop strong root systems without causing too much leaf congestion.
#8: Don’t Pinch too Early
Pinching is an excellent way to encourage lateral growth and produce short, stalky plants. But pinching too early in seedling production can cause undesirable growth and, in extreme cases, kill the plant. For best results, don’t pinch a cannabis seedling until you see four to six pairs of lateral shoots or “breaks.” Any sooner could result in a seedling shaped like a football goalpost.
#9: Try Some Creative Height Control
Ornamental crop growers use plant growth regulators (PGRs) to control height and produce robust seedlings. However, PGRs are not yet allowed for use on cannabis. Instead, growers wanting to control the height of densely packed seedlings should consider mechanical height control. This is simply the act of brushing seedlings by hand several times each day. The plants react by staying short and growing thicker stems. Some commercial growers outfit their watering booms with delicate material and run it over their crop throughout the day. It works wonders!
#10: Know When to Say Good-bye
All babies eventually need to leave the nest, and seedlings won’t stay young forever. Avoid stunting their growth by establishing a planting up or moving out date and sticking to it. If it’s too soon to plant outdoors, pot up inside, or send to customers, get innovative with your spacing options. Cramped conditions can negate the previous weeks of care and attention. The best growers will already have established a backup plan for this scenario long before the seeds are even sown.
Although the seedling stage accounts for only a fraction of the life cycle of a cannabis plant, it’s a vital step to ensuring a healthy and profitable crop. Fortunately, germinating cannabis seeds and caring for young plants is a pretty straightforward process. With a focus on timeliness and some attention to detail, the above ten tips should help ensure this year’s growing season gets off to an excellent start.
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