Green Thumb Academy 

Seed Starting

Starting off on the right foot can be essential to having viable seedlings, which will continue to thrive and progress to healthy, mature plants.

Here is a well known method of getting your seeds prepared for their journey.

You are going to need a few things to get started: Paper Towels, Shot glass (or small container of similar size), Hand towel, Seed Starting Medium (Soil, plugs, or blocks), tweezers to move seeds,  plastic tray and humidity dome.


You want to start with healthy viable seeds. Inspect your seeds for obvious imperfections such as being cracked or fragile, or other visible damage.

The Paper Towel Method
  • Step 1 - Fill your shot glass with room temperature water.

  • Step 2 - Drop your seeds into the shot glass. They should all float, but don't worry if one or two sink right away. The rest will sink once they have absorbed enough water.

  • Step 3 - Place the shot glass somewhere dark and cool for 24-48 hours. Check regularly and once they all sink, proceed to the next step. (Don't worry if some of the seeds crack open just a bit and the tap root starts to peek out. Just be very careful handling them)

  • Step 4 - Drain the water from the shot glass. Thoroughly wet a couple of paper towels and wring them out. Place the seeds on the paper towel and fold. Wet a facecloth or small hand towel and place it on top of the paper towel to insure it does not dry out.

  • Step 5 - Wait, while checking periodically, for the tap roots to appear. Typically you will see 1/4 to 1/2 inch tap roots within 24 - 48 hours. (Tap roots are very sensitive to touch and light so be cautious when handling them)

Babies First Home

So you have seeds with tap roots. Congratulations! While this first step can seem intimidating to new growers, I assure you it will become second nature as you gain experience growing.


But now what? Well, they need to be transferred to a new home where they can successfully mature from tiny seedlings to viable plants that we can work with.


That new home is probably most often a 16oz plastic cup with drainage holes cut into the bottom.


  • Fill it with some seed starter or a mildly fertilized soil like Happy Frog.


  • Poke a hole in the top of the soil just wide and deep enough to fit the seed and tap root.


  • Using extreme care (tweezers work great here), transfer the seed from the paper towel to the plastic cup, with the tap root going into the bottom of the hole.


  • Gently cover the seed with 1/4 inch of soil and lightly water. ( A mister is a good idea as you want to get a little moisture into the soil without soaking it.)


Typically you will have seedling popping through the soil within a few days, but some may be shy and take a bit longer to make an appearance.

**Rock wool or Rapid Rooter Plugs can be used as a seed starting medium as well. Rapid Rooters come prepared and moistened so place the plugs into the slots in a plastic tray and transfer the seeds to the plugs. Rock Wool  generally comes in small blocks with the hole already present. There are instructions on the package on how to prepare and PH the blocks with a nutrient solution prior to using them.**

Early plant life

Light, temperature, humidity, and a healthy medium are the most important ingredients to a successful start to your plant's life.

  • Light - A gentle light such as low powered LED or a T5, placed far enough away from the plant so as not to burn them.

  • Temperature - Temperature is very important to young plants. Too hot and you will cook them. Too cold, and this is the more frequent problem, and it can slow growth almost to a stop. 70-80 degrees at all times is a good place to be.

  • Humidity - Humidity is important to young plants. As the roots begin to develop in the soil, new growth in the plant above the soil will begin and that new growth will be somewhat dependent on the moisture in the air to feed it. High humidity is recommended for seedlings. 65-80% is a good range. Use a humidity dome if needed to maintain that range.

  • Medium - This can be soil in a cup, Rapid Rooter Plugs or rock wool in a tray. Keeping a healthy medium is important. Keep it moist, not soupy. Don't let it dry out completely. Keep it simple.

  • Nutrients? - Extremely young plants are at elevated risk of damage from nutrients. There should be enough trace minerals in your water, and nutrients in your soil to get your seedling off to a healthy start. (An exception to this would be if you use rock wool as it will require a very mild nutrient solution once the seedling starts to develop)

Next Steps - Preparing for a productive life

Now you have several seedlings in plastic cups (or Rock Wool or Plugs) and they have successfully made it through the early steps. What can you do to help them to be healthy and productive.


  • Feeding - Once you have a couple of nodes of growth, you want to start thinking about giving them a little bit of nutrient. The amount can vary depending on the nutrient line you choose, but typically 1/4 of the "Light Feeding" recommendation on the bottle will be sufficient.

  • Topping - Topping the plant when it reaches the point where it has grown a third or fourth node is recommended to start the process of training your plants to their optimal shape for mature growth.

  • Transplanting - Around the same time you are topping it will be time to transplant your seedling into the pot it will use for its vegetative growth period. Whichever you do first, wait a few days to allow the plant to recover before moving to the next step. If using Rock Wool or Plugs you will transplant the plug or block along with the plant. Don't try to remove the plant from the plugs.

Tips and Tricks
  • Plastic cups - If you put your soil in a clear plastic cup and then place that cup into a colored cup you can check the progress of your roots from time to time by just separating the cups.

  • Genetics - We cannot say enough about good genetics. Do your research and find good sources of seeds. Strong genetics lead to successful grows.

  • Seed viability - There are a number of suggestions out in the wild on how to check if your seeds are viable. Maybe you found an old pack of seeds from god knows when or a friend gave you a bunch of seeds that came from that "killer strain a few years back". Most likely, unless they were kept in horrible conditions, at least some of them are good. One way to check is to put a seed on a firm surface and press on it firmly but gently with your fingertip. If it breaks, it wasn't viable. This may seem a bit risky to some, as seeds bought online are quite pricey. But we really don't recommend it, nor should you need to do this for seeds you buy online. If you have seeds you are unsure of...plant them....whats the worst that can happen?

  • Temperature/Humidity - Be sure to get a Hygrometer with memory settings so you can check the high/low temps in your environment. Just because it is 75 degrees and 65% humidity at 5pm with the heat and lights on doesn't mean it is still in the sweet zone at night. KNOW YOUR ENVIRONMENT!!!