Can seeds get too dry?
Sir Coughsalot (Mr.80%… more like 60% now) here in sunny but dry AF Tucson, Arizona! My question is about seed viability and storage. I know the mantra of cool/dark/dry when storing cannabis seeds, but I am wondering what the limits for these parameters are. I have googled it quite a bit, but the information is half bro science, and half information for growers not living in extreme climates, you know, “normal” places where it rains more than twice a year! Here in the Sonoran Desert, we are in an EPIC drought and the humidity has been in the teens or even single digits for the most part for 2 years straight now. I struggle with humidity in my grow, but, believe it or not, you can do OK in 20-30% humidity which is the best I can do since I have to control heat as well. I use a 6gal evaporative humidifier at full tilt just to get that much. I used to run an ultrasonic huey, but the high PPM tap water killed it. Once I can afford an RO system, I will revisit the ultrasonic huey… but I digress…
I have been trying to germinate seeds I have been storing, but most seem to have no vigor and either never crack, or crack, spit out the tip of the tap root, then go kaput. I think a lot of it is… strain specific… and most seed’s viability starts going down steadily after 2 years. But then there are growers that store them for a decade or more and they pop like new… I have a feeling it is the way I have stored them. I have only been sealing them in the packaging and not in a mason jar or another air-tight container. All the packages were in a tin box with a huge silica pack and sitting in my 75F closet. I believe they might have gotten too dry and destroyed the embryo, which is not something most growers have to deal with.
What is the ideal humidity range to store cannabis seeds? I have seen as low as 5%RH and as high as 60% in my googlings. If I average everything i’m thinking it is about 20% to 30% RH. So I am asking the DGC.
Should I put them all in an airtight mason jar and store them in the fridge? I have pretty much burned through my old stock of regular and autoflower seeds and germinated about 1 out of every 10 of them. If I get a fresh pack of seeds ordered, BLAMO (see the pic) So I know it’s not my technique. My ultimate goal is to make some more autoflower seeds, but no point in making them if I can’t store them properly! And I can’t even make them if I can’t get a seed to pop! It’s almost like I need a boveda pack designed to hold 20% to 30% RH in the storage container?
E T H O S
• Short Term Storage: Seeds should be stored in a dry, cool, dark environment with consistent humidity levels under 50%.
• Evaluating Seeds: A good test to see if a seed is underdeveloped is to squeeze it between your fingertips. If it breaks, it most likely wasn’t viable. Older seeds may require encouragement to germinate such as sand paper on the shell or soaking in GA3.
• Germination: Seeds should be germinated in a sterile environment, allowing 3-4 days at 100% humidity for root growth, followed by gradual introduction to a less humid environment. When transplanting, ensure high levels of humidity for the first 72 hours.
• Temperatures: You want your seeds and seedlings in a warm room like your vegetative room. Ideally ambient temperatures should be low 70s – mid 80s.
• Humidity: Relatively high humidity is best for seeds and seedlings until they have adjusted to their larger pots.
• Sterilization: Sterilization is key to successful gardening, especially with newly-germinated seeds whose immunity has not yet built up and are increasingly susceptible to pathogens. Use H2O2 in warm water and make sure that tools, trays and gloves are sterile.
If you’re buying, popping or storing seeds, you know that there’s a proper way to go about taking care of your genetics for the best results. We’ve compiled some general recommendations on evaluating seed quality, proper seed storage, one of Ethos’ methods of germination, and a few tips on caring for your seedlings.
Judging A Seed By Its Shell: Evaluating Seed Quality
If you’re like us, you likely have at least one container of genetics you’ve purchased and/or bag seeds you’ve stumbled upon. If you’re only growing a handful of plants at a time, it would take years to pop them all, especially “bag seeds” or unintentional seeds from plants with intersex traits that are more likely to be sexually unstable. Seeds that are firm to the touch (and aren’t crushed between your fingers) are more likely to germinate. Large, dark seeds may require a light scuffing or soaking before putting them in the substrate as they are more mature seeds and have thicker shells.
A Note on Older Seeds
These seeds can take longer to germinate and may need help breaking out of their shell. Taking fine sand paper and scuffing the shell may help, as well as soaking the shell.
There’s a lot of loss of seed over time, especially the GA3 in that seed. When you soak that back in, the genetic is just as good as it was; it’s all about how vigorously the seed will pop out. As long as the seed is alive, you can soak that seed and then remove the shell and start the embryo (as long as the embryo is alive).
I like to use aerated warm water (80ºF). I put an air stone in a small container with the seed(s) so it’s more aggressive with that seed. I add 3% H2O2 and add GA3 at 100-500ppm, then soak for 24 hours before whatever germination method is being used. Anything over 10 years old, aim for up to 500ppm. Anything younger than five years, start with 100-200ppm.
For short term (up to three months), seeds can be stored in original product packaging in a baggie at room temperature and will likely be fine. More humid environments will necessitate a sealed container as fluctuations in moisture may begin the germination process unintentionally.
For longer term storage (up to easily 20 years), vacuum seal your seeds and keep them in a cool, dry area, out of any direct light exposure. For indefinite storage, you’ll want to nitrogen seal the seeds for ideal storage conditions.
Refrigerators are not optimum for proper seed storage because of the humidity fluctuations. Commercial refrigerators with humidity control would be exceptions to this rule.
When germinating, the most important part is having a sterile substrate for germination. Wet paper towels are common and work well as long as you are changing the water every day and moving the seeds around to prevent it from rooting into the towel. In these cases, I like to get seeds into the substrate after the shell is broken.
I don’t put seeds directly into soil or any kind of biological because of potential pathogens. Instead, I use straight coco or rock wool cubes (my preferred sterile substrates) in a clone dome with tray.
The primary concern when germinating seeds directly into a substrate, especially with organic matter, is that when the seed pops, it could succumb to damping, which is very common in soils. It only takes a single pythium spore to kill a seedling because seedlings don’t have immunity built up during the first 4-5 days of their lives. Often seeds will pop below the soil and die below soil from microbial failure or sprout up and die before they start putting out leaves due to these pathogens.
• Soak the seeds for 24 hours in warm water (with 3% H2O2) before putting them into rock wool cubes.
• Put the seeds at the very top of the cubes and then tear small pieces from the corner of the cubes to cover the seeds.
• The seed should be barely below the surface for easy viewing so you can adjust the taproot downward.
• You will typically want to keep them in those cubes inside the dome for 5-7 days to let the roots get strong enough before you transplant.
A Note on Germinating Autoflowers
When germinating auto flowers, it is incredibly important that you avoid breaking the tap root. Doing so will change how that plant grows, will dramatically reduce the yields, and is something that needs to be taken into consideration with all germination methods.
A Note on Sterilization
When using rock wool, use new cubes only, and, in general, new rooters and trays/cloning supplies will be among the easiest ways to ensure you have a sterile environment for your seeds. I recommend using H2O2 for your sterilization agent. You can often use other products in combination, but, for the grower on a budget, H2O2 is 10x cheaper and a great base product to begin with. More advanced growers can add tools to this arsenal as they understand their specific needs.
Caring for Seedlings
Depending on if your seedlings are auto flowers or photoperiod plants will determine how quickly you transplant to a larger pot.
For an auto flower seed, I’m going to transplant as early as I can into its final pot; not more than a week after the seed sprout begins.
For a photo period plant, I don’t mind allowing it to spend up to three weeks in the rock wool cubes as long as the grower understands how to care for rock wool. I take the dome off once all of the seeds have cracked and you have the first set of leaves (Cotyledon).
If you have a seedling that has difficulty popping off its shell, mist the shell several times a day; a moist shell is much more easily shed than a dry shell.
It is also worth noting that if you are transplanting your rock wool cubes into any other substrate other than rock wool, you should have a cover or a small layer of substrate covering the rock wool cube. This is important to maintain the moisture of the rock wool cube, which is vulnerable to drying out for the first 3-4 days. The cube needs to stay moisture these first few days before it will normalize water exchange with the surrounding substrate.
I suggest germinating in your veg room, where you want to be maintaining temps above 70ºF at all times. If you’re using a dome, you want your ambient temperatures in your room to be between 74-78ºF, keeping temperatures in the dome usually somewhere around 88-90ºF. If I’m not using a dome, I usually just put my seeds in cubes on top of heat mats.
If you’re in any situation where it does get cool or cold, I highly suggest a heating mat, but in a warm room, there’s no need. You don’t want hot water; you want water to be 70-85ºF max. I have found that I get the fastest germination at the safest rate in the upper 70s, right around 80ºF.
Note: When germinating with water at or above 80ºF, it is more susceptible to pathogens, so I suggest an H2O2 mixture whenever using warm water. You can warm the water in your substrate using heating mats or even placing on a warm surface.
Seedlings can handle a lot of light. During their first 3-4 days, they just want ambient, secondary lighting, even the flourescents in your normal home lights or T5s that are off to the side or away from a direct light source. Once they get rooting, they can handle exponential increases in light
so that, by the time they are 3-4 weeks old, they can be under 1000W bulbs.
I use incremental increases over four weeks. By week 2, I have seedlings at the full vegetative amount of light; seedlings can handle more light than a clone. You’ll be able to tell if your plants are light deficient as seedlings if they start over stretching; the most common symptom of light deficiency is over-stretching.
During the first 24-48 hours, you want your seed to be in near 100% humidity. When you transplant a seedling, the higher humidity in that room the better for the first week, especially the first 72 hours. You want to maintain optimum moisture without over-watering the rhizosphere, and moisture in the air helps the plants feed while roots search outward for moisture. If you are only adding moisture to your soil and your medium isn’t aerated enough, it could become too wet for the seedling to optimize its root growth.
With auto flowers, you want to make sure that you are using a highly aerated substrate in cloth pots or aerated pots. Because of the finite amount of time that they have to root, it is important to get maximum rooting. Using a highly aerated substrate (
30% perlite) can yield plants that are up to twice as big as a plant that’s in a much more dense soil because of how quickly it can root.