Cannabis Seedling Care (How To Keep Them Healthy)

Cannabis seedlings are delicate.

They have special needs.

Cannabis seedling care is not hard if you know what you are doing.

But if you don’t, those seedling may struggle to reach the vegetative stage in good health.

You want to provide the right temperature and humidity, along with the amount of light and water.

You also want to avoid common mistakes that can set back, and even ruin, your entire grow before it even really starts.

Keep reading to learn exactly how to care for cannabis seedlings to ensure they reach the vegetative stage in optimum health.

 

Cannabis Seedling Care

Once your marijuana seed has germinated and sprouted its first leaves, it will need water, light, and nutrients, just like more mature plants. But seedlings need less lights and nutrients. They also need a specific temperature and humidity range. Let’s get started there.

 

Temperature And Humidity For Seedlings

Seedlings like things hot and humid. At least in comparison to more mature weed plants.

The ideal temperature range for seedlings is from 68 to 77° F (20 to 25° C), with a relative humidity between 65 and 70%. At night, the temperature should be 5° or so lower.

 

Light For Seedlings

Seedlings do not need nearly as much light as mature plants. If your primary grow light is not dimmable, I would recommend against using it for seedlings. You would need to hang it about twice as high as the recommended height for vegging. That works, but it obvious wastes a lot of electricity.

Instead, I would just use regular fluorescent bulbs. Those give you enough light for seedlings. You can start with one bulb per seedling.

Or you can use a T5 fixture that covers multiple seedlings (however many fit below it). Your plants will tell you if they need more light (we’ll cover than below in the section on common problems). You can hang fluorescent lights much closer. Put them 2 to 4 inches from your plants.

If your main fixture is dimmable, then go ahead and use it. Dim the light way down so that it is about half as intense as the recommended setting for vegging.

As for how long to leave the lights on, go with the same schedule as for vegging. That means at least 16 hours of light per day, and 8 hours of darkness. I recommend 18 hours of light with 6 hours of darkness.

 

Nutrients And Water For Seedlings

If you are growing in soil, you probably won’t need to give your seedlings any nutrients at all, unless you are using nutrient-free soil. In that case, use about a quarter of the recommended amount of nutrients for vegging.

If you are growing in coco coir, another soilless medium, or using hydroponics, you will need to add cannabis nutrients. But again, use fewer than you would for more mature plants, meaning one quarter of the recommended amount.

As with mature plants, the pH of your water and growing medium is important. If the pH is not in the correct range, the roots will not be able to absorb the nutrients. You want the pH to be within these ranges.

• pH of 6 to 6.8 in soil
• pH of 5.5 to 6.5 in coco coir other soilless media, and hydroponics

Use your pH meter to measure the runoff (the water that comes out of the bottom of the pot). Adjust the pH levels of the water using pH up/down solutions to get it into the correct range. This article covers everything you need to know about water for weed plants.

 

How Often To Water Your Seedlings

If you put your seedlings directly into their final (large) pot, watering your plants will be slightly more complicated. The advantage of not needing to transplant your plants again is worth it for the first few grows, but once you’ve got a few grow behind you, I’d start putting seedlings in a solo cup and transplanting them later.

In a solo cup, simply give your plants water until it starts running out of the bottom. Then water again when the top inch of soil has become dry. If using coco, water every day or two. The top inch does not have to be dry before you water again, but it should not be completely wet either.

In a larger pot, you cannot give as much water, since the roots only take a tiny portion of the pot and waterlogging it will result in the roots not getting enough oxygen.

Instead, you should only give your plant a little water and only around the area where the roots are. Leave the rest of the pot dry. Then give a little more water in a day or two, when the area has mostly dried. If it dries sooner, water sooner.

Once your plants have grow a few leaves, you can begin watering as normal, meaning giving enough water so that it begins to run out of the bottom, then watering again once the top inch of medium has dried out.

 

Common Problems With Marijuana Seedlings

As mentioned above, cannabis seedlings are delicate. It is easy to provide too much of something, or not enough of it. And that can harm your seedlings.

We are now going to look at some common problems with cannabis seedlings and learn how to recognize them and how to fix them.

 

Overwatering

The most common problem with seedlings is overwatering, especially if you are growing them in a full-sized pot, instead of a smaller pot or a solo cup. But you can also get this issue from providing too much water overall, or from poor drainage.

Whatever the cause, when a cannabis plant receives too much water, it begins to look droopy. If your plant is looking droopy, examine all aspects of your watering routine to see if the plant is getting too much water.

If you are growing in a big pot, you should be watering as described above: just a little bit of water at a time directly around the area of the roots. If you are not watering like this, make that change.

Even in a smaller pot, if you are giving your plants water too often, they will suffer. Make sure you are letting the soil dry out (the top inch, anyway) before providing more water. Fabric pots let the soil dry more quickly, which is why we recommend those.

Also make sure you check the drainage from the pot. If you are using fabric pots with coco coir as recommended, this will not be an issue, But if not, make sure there is adequate drainage for water to escape from the pot and that the growing medium is not too thick (like clay). It should drain water well.

 

Underwatering

The symptoms of underwatering are very similar to the ones of overwatering. You seedling will be droopy, and just not growing properly. To tell the difference, look at the soil or growing medium.

If the medium is completely dry, the plant needs more water. The soil should always be somewhat moist. Only the top inch or so should be dry, before you water again.

Underwatering is not as common, but it is actually more dangerous, especially when combines with too many nutrients. In coco coir, that is not generally an issue, since you control the nutrients.

But if you grow in soil that already contains nutrients, it will almost certainly contain too many for seedlings. They can grow through this, but if it is combined with a lack of water, you have a big problem.

 

Malnutrition

Malnutrition refers to any issues having to do with nutrients. With seedlings, this most commonly means too many nutrients, but it can also mean a lack of them, or the wrong kind of nutrients.

The most common signs that your plants are getting too many nutrients are burned leaf tips and dark leaves, so look out for those.

The most common reason for nutrient toxicity is the use of a soil mix that contains a lot of nutrients. Seedlings don’t need so many nutrients.

As long as you water properly, your plants will get through this, But if not, they will suffer nutrient burn. You can avoid this issue altogether by planting your seedlings in a growing medium that does not contain nutrients. That is why I recommend using coco coir.

The other cause is simply feeding your plants too many nutrients. You avoid this by sticking to my recommendation of feeding your plants a quarter of the recommended amount of nutrients for vegging.

Of course, your plants could also not be getting enough nutrients. This does not always mean you need to feed more. If the pH level at the roots is not within the correct range, the roots are unable to absorb nutrients.

No matter how much you feed your plants, they will never improve as long as the pH level is too high or too low, so you need to make sure it is within the correct range.

Finally, you may be feeding your plants the wrong type of nutrients. this generally means they are not getting the correct ratio of nitrogen to potassium to phosphorous.

The easiest way to avoid this is to use a nutrient formula made specifically for cannabis. For seedlings, you should be using a nutrient solution made for vegging, not for flowering.

 

Lighting Issues

Lighting problems can basically take two forms: your plants are getting too much light, or not enough of it. If they are getting too much light, you will notice burned and crinkled leaves. Not enough light results in stretched out, overly tall seedlings.

Fixing either issue is easy. If you plants need more light, give it to them. Either lower the light closer to the plants, add more bulbs, or get a more powerful light.

If you are using fluorescents, you’ll probably need to add a bulb (or several). If you are using your primary grow light, you probably have it hanging quite high (as you should), so simply lower it some. Or dim it less, if you have a dimmable light.

If your plants need less light, do the opposite. Move the light further away from the plants or dim it more. For fluorescent bulbs, simply move them a little further away. If you are using a bunch of them, remove one (or several).

 

Heat

Seedlings need higher temperatures and humidity than more mature plants, but if things get too hot, they will suffer. You will notice symptoms like leaves turning up at the edges, spots forming on the leaves, or wilting.

To solve this issue, you need to reduce the heat in the grow room. If your light is too powerful, turning it down or using a weaker light will solve the problem for now, but you will still need to deal with this issue later in the grow when you need the light at full strength.

You should have ventilation set up in your grow area. You usually won’t need it for seedlings, but if you do, don’t hesitate to turn on your ducting fan. Your oscillating fan(s) should already be running anyway.

 

Transition To The Vegetative Stage

You’ll know your seedlings are ready to enter the vegetative stage when they’ve developed a few sets of true leaves. This shift usually occurs around 2-3 weeks from germination.

At this point, your plant is preparing for a period of significant leaf and stem expansion. Our article on what to expect from the vegetative stage will guide you through that period of your plants’ growth.

 

Caring For Cannabis Seedlings: Final Thoughts

Getting you sprouted weed seedlings from this early stage to the point where they are growing several sets of actual cannabis leaves is not hard, but there are a few key things to take care of and to look out for.

If you follow the guidelines above, you should get through this stage without any issues. It should take around 14 days, and then the real fun begins. Once in vegging, your plants will explode in size.