How To Provide Your Cannabis Seedlings With Optimal Care

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How To Provide Your Cannabis Seedlings With Optimal Care

Mistakes made during the seeding stage can impact a cannabis plant for the rest of its life, causing permanent damage or even death. Read this guide to find out how to avoid the most common pitfalls, all while promoting healthy growth, heavier yields, and better potency.

After germination, young cannabis plants enter the seedling stage. This period starts as soon as the first pair of true leaves emerge above the cotyledons, and lasts for two to three weeks. The seedling stage is over as soon as the plant develops 5–7 blades per leaf. That's when the vegetative stage begins.


Seedlings are more vulnerable to mould and disease at this point in their life cycle than at any other time. Any mistakes you make now can affect the plant for the remainder of its life. Stunted growth, low yield, minimal resin, and disappointing potency can often be traced back to poor care during the seedling stage. That's if you don't kill them outright.

Here's how to provide your seedlings with optimal care during this critical period:


Start your seedlings in small pots when growing in soil to promote healthy root growth. It will be necessary to transplant to a bigger pot a couple times during the plant's lifespan. This might sound like a lot of work, especially when plants will survive even when germinated right in their final pot, but the difference in health and yield make it well worth the extra effort.

Small pots encourage a tight root ball, and a tight root ball makes cannabis plants sturdier later in life by lowering their center of gravity. Without it, the sheer weight of resin-drenched flowers near the top of the canopy can literally pull a plant up by its roots if the main colas start to tip to one side. Providing an adequate support system can also prevent this type of damage.

Pot size helps promote healthy seedlings in other ways as well. A well-developed root system delivers more water and nutrients to the developing plant, promoting healthier foliage and bud formation. Small pots prevent root rot because stale water is less likely to pool at the bottom of the container, where it can literally rob your plants of oxygen as they drown.

Some people transplant to bigger pots on a schedule, or as they see signs of the plant becoming root-bound. If you see roots extending from the bottom of the pot, stalled growth, or the soil dries out in less than three days, it's time for a bigger pot.

Autoflowering seeds are an exception to this rule. They tend to do best when planted in their final pots right from the beginning.


Overwatering is one of the most common mistakes new cannabis growers make at every stage, but it's especially harmful during the seedling stage. Too much water can cause seedlings to dampen off; this is when the stem rots off right above the soil. On the other hand, you don't want to let your seedlings dry out completely either.

Using a small pot will prevent this problem for the most part, but there are a few other things to be aware of. Make sure your pots have drainage holes and that you use a soil or soilless mix that drains well. This will help prevent issues that can arise when you give your plants too much water all at once.

However, most cases of overwatering don't occur because you gave your plants too much water at one time; it happens because you water too often. Use the weight of the pot as a guide to let you know when your seedlings are thirsty. Learn how heavy the container feels when it's completely dry, and when it's saturated. Give your seedlings a thorough watering when the pots lose about two-thirds of their weight. Always empty your drip trays and wipe up any spills.

If you don't trust your own judgement enough to go by weight, use a spray bottle to give them a heavy misting with clean water every few days.

Watering too often can also make the roots lazy because they don't have to work as hard to stay hydrated. By allowing the soil to dry out slightly, you can encourage the main roots to send out new shoots to search for moisture. These extra shoots create a more robust, well-developed root system.

If your plants get too dry, they will wilt or droop. Water immediately as soon as you see this happen. Overwatering has a similar symptom, but in this case, the leaves hang down because they're so heavy with water. If this happens, make sure your pots are draining and allow them to dry out for several days.


Cannabis seeds have enough stored energy inside the shell to support germination and the first few days of life. After that, they'll need to take in nutrients from their grow media. However, during the tender seedling stage, they can't handle strong feed without damage. Overfeed a little and you'll burn them slightly. Overfeed by a lot and you'll kill them.

This is why you should plant seedlings in a starting medium that doesn't contain a lot of fertiliser. Old soil from a previous grow will do as long as you either grow organically or flush the soil well to remove any salt buildup. Otherwise, most garden shops have soils designed specifically for this stage of growth.

As long as you see new growth daily, your seedlings are getting enough nutrients from their media and don't need to be fed. If growth stalls or you see the new leaves start to yellow, feed them with a mild fertiliser intended for seedlings. Most of the time, you can use about half of what the manufacturer recommends for commercial fertilisers. Always check the pH of your mix before feeding; cannabis grown in soil prefers a pH level of 6.5.

Keep in mind that some cannabis strains are light feeders, and some are heavy feeders, and this can even vary within an individual strain by phenotype. Always start feeding lightly and increase the nutrient strength as your plants adjust, so you can see how well they tolerate each feeding. By observing them closely, you'll get to know your genetics and what they need.


A weak stem during the seedling stage will haunt you throughout your entire grow, leading to flimsy branches, minimal nutrient uptake, and small, fluffy buds. You also want to avoid tall, leggy seedlings that can't even support the weight of their first sets of true leaves.

To minimise stretch, provide your cannabis seedlings with adequate light. Nodes should be fairly tight at this point. If you have more than a couple centimetres between leaf pairs, lower your lights to reduce vertical growth.

At this stage, seedlings don't need a lot of light, but they need some. CFLs or low-wattage LEDs will work as long as you keep them close to the plant. If you use MH or HPS lighting, keep them about 30cm away and stick with a 400W bulb. If you notice any type of burning or crinkling, lift the lights higher.

To increase the girth and stiffness of the stems, use an oscillating fan to blow a steady stream of air over them. To compensate for the stress, the seedling's stem will grow stronger. If you can't use a fan, brush your fingers across the top of the seedlings twice a day.


Because the root system is not yet fully developed, cannabis seedlings need higher humidity levels and steadier temperatures than older plants. Use a thermo-hygrometer to keep an eye on each; inexpensive digital tools that measure both readings are easy to find online, in pet stores, and in grow shops.

Cannabis seedlings prefer relative humidity to hover around 70%. Overall temps should stay within the 20–25°C range.

Excess heat will make the leaves crinkle or turn up at the edges for a taco-shell effect. Excess humidity can create problems with mould or rot. If it's too cold, your seedling's growth rate will stall. Very low humidity levels will make the leaves dry out and develop brown spots.

Protect Outdoor Seedlings with a DomePROTECT OUTDOOR SEEDLINGS WITH DOMES

If you're growing outdoors, you have to safeguard your seedlings from additional dangers. A late frost, hungry insects, and local wildlife can quickly put an end to tender young plants.

To protect them from physical harm, cover them with a protective dome. You can make one yourself by cutting the top off an empty soda bottle or plastic milk jug. This will protect them from cold temperatures and hungry mouths while maintaining humidity levels in dryer climates.

But, don't let it get too humid inside the dome. Excess moisture can encourage mould growth and rot. If you notice a lot of condensation inside the dome, puncture it a few times to allow for better airflow.


Giving your seedlings the proper care from the start takes time and attention, but it's an investment that pays off down the road in the form of healthier plants, bigger yields, increased potency, and improved bud quality. Improper feeding and watering are the most common problems, but inadequate lighting and airflow, as well as temperature and humidity fluctuations, can have a dramatic impact on your plants for the rest of their lives.