Marijuana seedlings are like children. They grow faster and healthier when you nurture them through a steady and sustained program of lighting, feeding and watering. Well, they’re sorta like children. And yet many growers make mistakes that end up injuring, even killing their seedlings.
In this post we’ll help you avoid the most common mistakes so that your seedlings get their best start in life.
Marijuana Seedlings Need Light That’s Kind
I start out by germinating my marijuana seedlings in peat pots or rockwool cubes.
When I first embarked on my grower career, if seedlings were intended for an outdoor garden, I used to place them in bright sun right away. Sad to say, I found out the hard way that direct sun was too much for the little guys, especially as I lived in high-UV areas at the time. I could see their leaves turn downward as they shrunk away from the beating sun. I learned that marijuana seedlings grown outdoors prefer mixed shade for the first 2–3 weeks of their lives.
Here’s another thing I did when first starting out. If my seedlings were intended for an indoor grow op, I would put them under 250-watt or 400-watt metal halide grow lights. Yet even though I had the grow lights placed three or more feet above the seedlings, the light intensity was still too much for them.
Quite simply, tender young leaves aren’t ready for high-intensity lighting. That’s why most growers use fluorescent grow lights or low-power LED grow lights for the first three weeks of grow phase (if not longer) before putting the plants under either high-intensity discharge, or HID, or full-power LED lights.
Encouraging Root Growth: What Are The Best Products To Use?
Leaf growth and root growth are essential for marijuana seedlings, and root growth is what drives leaf growth.
There are several supplements and nutrients you can use to encourage root growth:
- Vitamin B, such as that found in a hydroponics product called B-52. For plants less than three weeks old, I only use 1–2 ml of this product per gallon of water, and I don’t use it every watering cycle. It contains small amounts of nitrogen, phosphorus and potassium, which are added benefits for early growth.
- House & Garden Roots Excelurator: A high-priced but highly effective root stimulant product.
- Beneficial bacteria and fungi. In nature, plant roots evolved with microbes that protect, stimulate and enhance roots. You can add those microbes into your root zone using hydroponics products made especially for marijuana. Such products include Advanced Nutrients’ Voodoo Juice, Tarantula and Piranha. I recommend 1–2 ml per gallon of water for each of these products, starting two days after your seedlings produce their first set of true leaves. As your seedlings gain leaves and height, begin to follow the manufacturer’s dosing instructions.
Nutrients & Stimulants Specifically For Marijuana Seedlings
Many growers make the mistake of starting to feed their seedlings too early, too heavily, or both.
When a seedling only has a few sets of true leaves (by “true leaves,” I mean leaves with serrated edges), it has minimal root development and can’t handle high nutrients doses.
Other than overwatering, which is a sure way to kill seedlings, over-fertilizing is also a leading cause of seedling failure.
It makes a big difference if you’re growing in inert media such as rockwool, soilless mix or coco coir, in pure hydroponics such as deep water culture, or in soil.
If you’re growing in inert media or pure hydroponics, there are no nutrients in your seedling’s root zone and you have to provide them beginning a day or two after your seedlings produce their first set of true leaves.
But you want to be very conservative in how much and how often you feed them.
You definitely don’t use your nutrients at full strength, or even half strength. When I’m using pH Perfect Connoisseur grow phase base nutrients, for example, I use only 10–15 percent of the full-strength dose.
With seedlings, less is more. Your plants can sometimes recover if you give them too few nutrients. But if you give them too high a dose, you burn their delicate young roots — and your cannabis seedlings will likely never recover.
If you intend to grow marijuana seedlings in soil, ask the soil manufacturer ahead of time if the soil you want to use is meant for seedlings.
Some manufacturers load their soil with too many nutrients, especially nitrogen. This soil is good for transplanting established plants into, but it’s too nutrient rich for seedlings.
More Top Tips For Sturdy Seedlings
I have three more tricks to help your seedlings survive. First, place a small oscillating fan so it blows the seedlings gently, from side to side. This will help to strengthen their stalks, so the plants grow to be sturdier later on.
Another tip is to use reverse osmosis water, rainwater, or tested and clean well water.
Marijuana seedlings are very sensitive to chlorine, chloramine, pollution, pesticides, and other contaminants found in most municipal water supplies. Use reverse osmosis water and your sprouts will thank you for it.
Thirdly, give seedlings an environment with 57–67 percent relative humidity for the first 1–3 weeks of their lives. I’ve seen grow ops in Southern California (where outdoor humidity levels can be as low as 15 percent) that have indoor air so dry that seedlings died.
Those growers were forced to use humidity domes or humidifiers so that the next seedling crops survived.
Of course, seedlings don’t usually need a humidity dome like young clones do, but seedlings need the aforementioned humidity range until they’ve developed root systems adequate enough to draw moisture from below.
So now you’ve got the lowdown on giving your marijuana seedlings the best start in life, what’s stopping you on your path to grower glory?