Starting Cannabis Seeds In Solo Cups


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Beginner’s how to guide to germinating cannabis seeds, plus early seedling stage of cultivation. Specific to outdoor autoflower growing in soil. In this article, you will see how much cannabis seedlings have grown after one week under 12/12 lighting in Red Solo Cups, and under Agnetix LED lights.

How To Grow Cannabis #2: Germination and Seedling Stage

Disclaimers: NOT FOR SALE OR TRADE. The following post features content about cannabis cultivation and other related substances that are illegal under federal law as well as under state law in certain states. This content has been produced by Thunderbird Disco—located in the Commonwealth of Virginia—for educational and entertainment purposes only. All cultivation described below was completed in accordance with Virginia law as authorized in § 4.1-1101 Home cultivation of marijuana for personal use; penalties.

Ok, so you’ve got some cannabis seeds that you found on the side of the road, or were maybe gifted from a friend in the same state. Nice job!

The next step is to germinate these seeds. Again, I’m growing outdoor, in soil, and was gifted three autoflower strains, so everything below is specific to those parameters.

If you’re growing outdoors and want to maximize your time, plan to start germination a few weeks before the last spring frost date in your region, so by the time the weather is warm enough and risk of frost is gone, you’re ready to move these ladies outside.

This won’t all make sense yet, but here’s a handy dandy week-by-week outdoor autoflower cannabis growing cheat sheet for all your watering, nutrient and general maintenance needs


White paper towels (no dyes or patterns)

Liquid seaweed (I used Neptune’s Harvest)

Glass measuring cup (something with a spout)


Step 1: First Soak

Pour purified water into measuring cup and add just a drop of liquid seaweed. Stir. If you’re growing multiple strains, don’t mix all the seeds together in one vessel! Label different glasses with the different strain names and pour some seaweed water into each glass. Place your seeds in this water and let soak for about 24-48 hours in a warm, dry, dark place.

Step 2: Second Soak

Add another few drops of liquid seaweed to some purified water. You’re going to make this little wet paper towel sandwich with your seeds in the middle (follow this video). Stack 2-3 paper towel squares, fold in the corners to make into a diamond, place it on a dinner plate and then wet it down with seaweed water. Gently spread your soaked seeds onto this paper towel (again, keep the strains separate, and transfer the label from the glasses to the dinner plate). Now add another stack of 2-3 folded paper towels on top, and again wet it down. You want this stack to be wet but not soaking (no standing water on the plate). Plan to leave this for another 24-48 hours.

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Step 3: Keep Moist

Don’t let the paper towels totally dry out. Check every 8-12 hours or so and add more seaweed water as needed.

Step 4: Check for Taproots

After 48 hours, very carefully peel back the paper towel and check to see if there’s a taproot coming out of each seed. The root is likely a bit stuck to the paper towel, so go very slow and make sure you don’t damage this sprout while you’re peeling off the paper towel. If you see taproots, go on to the next phase. If not, let the seed sit in the moist towel for another day or two.

Once you have your taproot showing…



pH Meter (I used this)

pH Adjusters (General Hyroponics pH Up/Down, or distilled white vinegar)

LED Grow Light (I used something basic like this)

Hydroton clay pebbles (optional, like this)

Seedling Heat Mat and Thermometer (optional; like this)

NOTE: You’ll find some videos online (like this one from Homegrown) that recommend first planting germinated seeds in Solo cups and then transplanting to larger pots or grow bags…but this is only for photoperiod plants. I accidentally did this with my seeds and the transplant process either killed or at least stunted my autoflower plants, which aren’t as robust and don’t have as much time to recover from the stress of transplanting. Plus, it’s an annoying extra step. Having tried it both ways, I highly recommend planting germinated autoflower seeds directly into the pot or grow bag that they’ll live in forever. You can see the side by side comparison below.

Step 1: Prepare Grow Bags

Add a 2-inch layer of Hydroton to the bottom of your grow bags (optional, but helps strike a balance between good drainage and moisture retention). Fill bags most of the way with Fox Farm Ocean Forest super soil (a favorite among growers you’ll see abbreviated as “FFOF”).

Don’t press down or pack the soil in there, keep it light and fluffy.

Step 2: Add Seed Starting Mix

Scoop out a small bowl’s worth of FFOF and in that center hole add in some of the Light Warrior seed starter mix. This stuff is a little lighter and has less nutrients so it won’t “burn” the tender sprout. But as the taproot grows and the roots begin to establish and stretch out, they’ll reach the “hotter” FFOF mix once they’re strong enough to handle it.

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Step 3: Prepare pH-Adjusted Water

You can take your chances with water straight from your tap, but it’s most likely not in the ideal pH range of 6.0 – 7.0 that autoflower cannabis plants require. Proper soil pH is what determines how well your plants can uptake nutrients, and anything too far out of the optimum range will be like they’re drinking through a pinched straw.

Use your properly-calibrated pH meter to test your tap water. Mine was in the 7.5 range, so I needed to adjust down. You can use professional products (like these) but I just added a little distilled white vinegar to make the water more acidic and bring the pH down. You only need a tiny bit, like 1-2 ml per gallon of water, to shift the pH, so go slow and see what it takes to get close to that sweet spot of pH 6.5. You’ll be using pH-adjusted water throughout the grow process, so might as well start practicing this step (don’t make the mistake I did, thinking this was a complicated an unnecessary step; bad pH can lead to all kinds of problems).

Step 4: Moisten Soil in Grow Bags BEFORE Adding Seeds

Saturate your grow bags with this pH-adjusted water to moisten the grow medium. Do this before adding the seeds, or else you risk disturbing the seed or having it float away.

Step 5: Add Germinated Seeds

Gingerly place one germinated seed in the center of each wet grow bag (the area with the Light Warrior Seed Starting Mix), taproot facing down. Just barely cover it with soil. Make sure you continue to track which seeds/strains are in which bags, adding plant labels to the bags or to the soil. Place plastic wrap over the top of the grow bag and secure with clips. Poke a couple holes in it to create a nice warm terrarium kinda thing.

One week under 12/12 light cycle in a Red Solo Cup

Can you grow weed in a red solo cup? Can you skip the vegetative stage and go straight to the 12/12 light cycle? We have always wondered if this was possible, so we decided to try it ourselves.

In this video series, we document the process of planting seeds in red solo cups, and then putting them under 12/12 lighting.

In this episode, we review our seedlings after their first week in the flower room.

Growing Marijuana From Seed in a Red Solo Cup

For this experiment, we used regular seeds from Sin City Seeds, that included the strains Rainbows at Night, Hard Cider, and Cart Wheels.

We sprouted the seeds using the paper towel method. And once we had tails, we put them in a red solo cup with coco coir.

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Using the 18/6 Light Cycle for young cannabis seedlings

In Part 1 and Part 2, our seedlings remained in our Veg Room under the typical 18/6 light schedule that is used during the vegetative stage. We kept them there for a total of 19 days, counting from the day the seeds were “planted.”

During that the first week, we filmed the seedlings at five days old. At that size, they were definitely not something you would want to flower. They were just a couple inches above the dirt.

By the second week, we could have put them under 12/12, but at less than five inches, it just seemed like a good idea to get another week’s worth of growth at the 18/6 interval.

Our “12/12 From Seed” Experiment actually had 19 days under 18/6 light cycle

By the third week, our plants were a total of 19 days old and we decided to flower them at that point. They were about the size you would want if you were purchasing a clone from someone. By any standard, still very small plants.

So although we are calling our experiment “12/12 from Seed,” it is really “19 days of 18/6 then 12/12.”

Is this a true “12/12 from seed” experiment? Yes and No. It doesn’t really matter. You still get to see what a seedling is capable of, even with 19 days of vegetative lighting.

Flowering Cannabis in a Red Solo Cup

After one week of flower, the plants have definitely grown. (On second thought, maybe we didn’t need those 19 days under veg lighting after all?)

You can see that the plants have become noticeably bigger. And it’s only been one week under 12/12 lighting! The center nodes are priming to be flower sites. The fan leaves are large and drooping over, soaking up the light.

There’s been no pruning or defoliating on these plants. Not that any needs to be done. But the take away here so far is that it definitely looks like you can flower a plant in a red solo cup. The Agnetix LED lights are very powerful, so this should be an exciting run.

These plants are bigger than they were last week, and they look like they are ready to produce bud in the coming weeks.

In the next article, we will review the plants after conclusion of their second week under 12/12 lighting.

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