Transplanting Cannabis Seedlings: How to do it correctly

Guest post from Grow Weed Easy

When it comes to transplanting cannabis seedlings, it takes some finesse.

As your little seed moves through its early stages of life, it will need some special care and handling.  And depending on whether you're growing indoors or out, soil or hydroponics, you'll need different techniques.

Always keep one thing in mind, marijuana seedlings are babies and are likewise delicate. 

Young seedlings are not ready for direct sunlight, full-strength grow lights, or nutrients. They need to have a moist environment, but not so much so that they sit in mud or are drowning.

If you're planting in soil, start with a balanced potting soil that doesn't contain extra nutrients. I recommend Happy Frog potting soil mix for young cannabis seedlings, but any plain potting mix from your local garden store will do.

Never use Miracle-Gro soil or any soil that has "time-released" nutrients already mixed in.  

How to Transplant Cannabis Seedlings

transplanting cannabis seedlings

Your seedlings have a couple of leaves and maybe even some roots out the bottom of planting cube you used.  Fill your pot with the soil and pack down.  Then dig out a hole the size of your cube.  

Place the cube with the seedling in the hole and pack soil around it.  Water and place into it's growing environment, making sure the light is not too intense or direct.  You can use a small 3 gallon pot here, or plant it into it's final large pot.

Some like to do less transplants and transplant plant cannabis seedlings into their final container. But this can cause issues if you're not careful.  More on this in the what size pot should I use article.

Others, due to space, time or other considerations will transplant plant cannabis seedlings into interim pots first.  

If you're using a good quality soil, extra nutrients or fertilizers are not needed for several weeks.

Nutrient, Water, and Light Considerations When Transplanting Cannabis Seedlings

If you're planting in coco coir, a soilless medium, or hydroponics, only add cannabis nutrients at seedling strength, or 1/4 the regular strength, until your plants have grown a few sets of leaves. Then you can slowly start working your way up to full strength nutrient levels.

With young marijuana seedlings, less is more.

In general, if you are growing in soil, your water pH (acidity level) should not be an issue.  If growing hydroponically, water pH is very important and needs to be checked regularly.

 Some growers get lucky and happen to have water with the right pH, but if you're noticing deficiencies and problems with your seedlings, definitely take the time to understand about the pH of you water and how it affects the plant's overall health.  

If you plan on growing indoors under high intensity grow lights (such as HPS or MH grow lights), you may want to start them out with less intense fluorescent grow lights or compact florescent bulbs (CFLs).

Or just keep your high intensity grow lights several feet away at first, and slowly move lights closer as your seedlings gets older.  CFL bulbs (twisty/spiral bulbs) are a great source of light for young marijuana seedlings

CFL lightbulbs used after transplanting cannabis seedlings
  • CFLs provide the right types of light for seedlings
  • CFLs are extremely cheap to buy
  • CFLs are easy on your electric bill
  • CFLs can be found almost anywhere, at your local hardware store, supermart, grocery store, or online

Keep CFLs or flourescent lights about 6 inches away from your seedlings. Place your hand where the leaves are to make sure it doesn't feel too hot.

If it's hot for your hand after 10 seconds, it's too hot for your plants.

Once your seedlings have developed their first two sets of leaves, then you can move these lights as close as 2 inches away as long as the lights aren't too hot.

Make sure to keep a close eye on your seedlings to ensure they don't grow too close to the lights and burn themselves. Seedlings can grow fast, and many growers have been surprised to find plants have actually grown into the light overnight.

If new seedlings are showing signs of stress (pale color, wilting or browning leaves or generally weak), try moving the lights further away and see if that helps.

What to Look for in Healthy Marijuana Seedlings

Once marijuana seedlings are about fourteen days old, they're ready be treated as if they're in the vegetative stage.

The following pictures are the early stages of healthy plants grown hydroponically.

Two round cotyledon leaves, then two "real" (serrated) single-finger cannabis leaves.

transplanting cannabis seedlings

Next, the single-finger leaves expand, and the next set is usually 3-finger leaves

transplanting cannabis seedlings

Next, the cannabis plant will start making 5-finger leaves

transplanting cannabis seedlings

Finally, most cannabis plants stop at 7-finger leaves

transplanting cannabis seedlings

Make sure you learn about plant training techniques to make the most of your time in the vegetative stage!

What Size Pot Should I Use for Transplanting Cannabis Seedlings?

When growing cannabis plants in a container, you have to choose the size of your pot. A general guide is to have about 2 gallons per 12" of height. This isn't perfect, since plants often grow differently, but this is a good rule of thumb.

When in doubt, get a bigger final container size as opposed to a smaller one. Plants that get rootbound from being in a too-small container will grow more slowly and be prone to problems.

It's not good to transfer plants during the flowering/budding stage, so you want to have your cannabis plants in their final container at least 2 weeks before the beginning of flowering/budding.

Final Container for Desired Plant Size - General guide

  • 12" ~ 2-3 gallon container
  • 24" ~ 3-5 gallon container
  • 36" ~ 5-7 gallon container
  • 48" ~ 6-10 gallon container
  • 60" ~ 8-10+ gallon container

Best size pot for your cannabis seedlings?

transplanting cannabis seedlings

For fastest growth rates, it's better to plant young seedlings or clones in a very small container, like a disposable plastic solo cup.

For new seedlings and clones, use a small container if possible

The reason you want to start with a small container is that your plant's young roots thrive on oxygen. Cannabis plant roots "breathe" oxygen, just like we breathe air, and it's important that young cannabis roots get plenty of oxygen so the plant can grow as fast as possible.

However, young plant roots do not drink much water yet. When you water seedlings or clones in a very big container, they will use up all the oxygen quickly, and the large size of the container will prevent the growing medium from drying out.

A big plant will drink up all the water quickly, but with seedlings, you're basically waiting for the growing medium to dry out by itself.

While you're waiting for the container to dry out, your cannabis roots are sitting in a wet environment and not getting much oxygen, slowing down their growth rates.

Poke holes in the bottom of your cup so water can drain out easily!

By planting young seeds in a small container with holes in the bottom, the growing medium will dry out much more quickly, allowing you to water more often. The young cannabis will get plenty of oxygen and water.

Alternative to Solo Cup: Start plants in seedling cube

transplanting cannabis seedlings

If you don't want to have to transplant your young plants, you can start them in a seedling plug or cube and wait until you start seeing roots come out the bottom. At that point, they will be ready to be transferred to a larger container.

What happens if I plant seeds or clones in a big container?

Your cannabis seedlings and clones will definitely survive in a bigger container; they just won't grow as fast for the first few days or weeks because they aren't getting as much oxygen.

 With a bigger container, you will need to wait longer between waterings, and during that time your plant roots will be getting reduced oxygen.

If you've planted your young plant in a large container, try to give only a little bit of water at a time (enough to wet the area around the seedling roots) until the plant is growing vigorously. Once the plant has grown a few sets of leaves, you should start watering cannabis normally so that water drains out the bottom.

About the author 

Mitch Mandell

Mitch Mandell is the publisher of Senior Stoner, a partner in Z-Dog Media, and a long time cannabis enthusiast and cultivator. Prior to entering the world of publishing, he had a long career in advertising, working for some of the country's top agencies.

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