Everything About Cannabis Seedlings

Max Sargent

Cannabis Journalist & Psychedelics Expert

Max Sargent

Last updated: December 26th, 2022

Whether this is the case for you or not, properly caring for cannabis seedlings is vital to ensure healthy plants and big crop. Here’s what you need to know to optimise the health and development of your seedlings.

What are cannabis seedlings?

Cannabis seedlings are cannabis plants in their first iteration. They are the equivalent of a newborn baby through to a toddler. And cannabis seedlings are just as fragile and in need of care as their human equivalent!

As soon as a seed splits open and the first pair of leaves (cotyledons) show themselves—this is a cannabis seedling. Soon, it will push aside its seed casing and drive its taproot down into the earth (or other growing medium). From this taproot, a sophisticated and extensive root system will begin to develop, through which the plant will absorb water and nutrients.

If a seedling gets a good start in life, the chances of it developing into a productive and potent cannabis plant are much higher than with a seedling that has to battle for survival. Therefore, understanding cannabis plants in the seedling stage is crucial to securing a good crop.

What are the requirements for healthy seedlings?

So, how do you rear a healthy cannabis seedling? Fortunately, it’s not so complex. Despite the comparison to human babies, cannabis seedlings are actually much more capable of looking after themselves. Nevertheless, they need a suitable environment in which to do it.

Correct container

Starting seedlings off in a suitable container is an easy way to give them a good start. Seedling containers should:

• Be small, so they don’t hold excess water

• Perhaps have a covering, like a propagation chamber, to maintain high humidity (this is great for germination too)

• Have holes in the bottom for drainage

Note: If you’re planting autoflowering cannabis seeds, it might be worth germinating them in their final containers, as any damage to the roots that occurs during transplantation can be hard to reverse.

Correct growing medium

The root systems of seedlings are delicate, and as such they need hospitable growing media in order to thrive. In most cases, a high-quality potting soil is perfect for housing cannabis seedlings. It should already contain adequate nutrients to sustain at least a few weeks of growth, so you won’t have to feed your plants until they have moved into the vegetative stage, or perhaps even later.

Whichever growing medium you choose, here are some key considerations:

• It shouldn’t be too dense, as young roots need space to grow.

• It should hold water well-enough that it stays moist, but not so well that the roots drown.

• If you use inert media, you will need to add nutrients to it. Just be very careful, as seedlings are particularly susceptible to overfeeding.

Correct watering regime

Seedlings don’t like to get soaked, nor do they like to dry up. Watering cannabis seedlings is a tricky task, and it’s worth being conservative. It may be that they don’t need to be watered at all, depending on how you are growing them.

Gently put a finger into the soil; is it bone-dry? Alternatively, lift the pots; are they surprisingly light? If the soil has totally dried out, then you’ll need to add a little water. To do this, use a mister or an attachment like a showerhead to avoid knocking your seedlings over or disrupting the growth of their roots. Water minimally—they don’t need much.

Misting Bottle (Zamnesia)

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Other considerations are:

• pH level: Good soil should already have the correct pH level, so you may not need to adjust your water. But be aware that tap water usually has a pH of 7.0 or higher, whereas cannabis grown in soil likes a pH level of 6.0–7.0. So if your water is above 7.0, consider reducing the pH a little with a "pH down" solution. To do this, you can use purpose-made products, which are easily accessible online or from gardening centres, or you can make a solution using the natural acid of lemons, for example.

• Don’t add fertiliser!

• Don’t water if you intend to transplant very soon.

Quality lighting

For most of a cannabis plant’s life, you’ll probably have it under HPS or LED lighting (if you use artificial lights). Seedlings, however, thrive best under CFL lights. These emit light at the blue end of the spectrum, which is best for young plants as it stimulates root development, simulating the light of spring. Exposing seedlings to 18 hours of light per day is suitable, but make sure the light isn’t too intense or strong. Seedlings don’t like to get burnt!

If growing outdoors, your climate and location will dictate where you germinate your seeds and house your seedlings. If growing in a warmer, southern European country, or germinating later in the spring, then you can plant your seedlings outdoors right away. If, on the other hand, you're in a cooler location or germinating early, then you could try putting your seedlings on a windowsill first, or use CFL lights. Be aware that, when situated on a windowsill, your seedlings might stretch in the quest for greater light.

When to transplant cannabis seedlings

With photoperiod plants, people tend to transplant seedlings at around 10 days. At this point, a plant should have at least three true sets of leaves.

As mentioned, autoflowering cannabis doesn’t like to be transplanted. This is because it automatically switches to the flowering stage very quickly, meaning its roots won’t have time to recover from any damage that happens during transplantation. It’s best to germinate auto seeds in their final pots.

Caring for cannabis seedlings: a simple pleasure

Looking after cannabis seedlings isn’t too complex, but it has big implications. Plants that get a good start in life find it much easier to develop properly, which ultimately means a better haul come harvest time!