by Nebula Haze
A grower purchases 3 seeds of the same strain, and 2 of the plants are doing great, but one is struggling. For some reason even though it’s getting the exact same environment, it’s still growing slower than the others.
Why is one cannabis seedling smaller than the others in the same environment?
The most common reason is…
1.) Plant Wants Less Water
One of the most common reasons seedlings grow slow is they are overwatered. This is often accompanied by general droopiness. Some plants simply drink more than others, which is why the amount of water that’s good for one plant may be too much for another plant. When one seedling is growing slower, watch it closely to see if it may be getting droopy after watering. This problem can compound if you keep giving all your plants the same amount of water because as the size difference grows, the smaller plant needs less and less water compared to the others.
If a plant is perpetually droopy, it often needs less water. Especially if the pot feels heavy, too.
Small plants don’t need much water yet. Just a small circle around the base.
Overwatered young plants often show deficiencies even when everything else is right.
Other common reasons one cannabis plant is growing slower than the others:
2.) Started from an Old, Small or Flimsy Seed
Some of my favorite plants ever have come from small or flimsy seeds, so I highly recommend sprouting them anyway if it’s a strain you want. The size of the seed doesn’t tell you how the weed will turn out.
That being said, tiny seeds have tiny seedling embryos inside and often take a few extra days or a week to really “get growing” compared to seedlings from average size seeds. Old seeds (even properly stored) and certain strains also tend to germinate slow and start slow, regardless of germination technique.
Learn the easiest way to germinate seeds here.
3.) Slow or Poor Germination
If a seedling goes through stress during germination, it can cause that plant to grow a bit slower at first. On the other hand, seeds that germinate fast tend to start growing fast right out the gate.
Randomly, some seedlings just germinate and grow faster than others.
Common: All seeds germinated at the same time, but seedlings are at different stages. Click for closeup.
4.) Nutrient Deficiencies
When cannabis plants turn yellow all over, they usually need more nutrients overall.
Sometimes plants need more nutrients.
Nutrient Deficiencies Caused by pH
If leaf discoloration is appearing most on hard-working leaves under the light (even though the grow light is the recommended distance away), the cause is often incorrect pH at the roots.
Nutrient deficiencies caused by pH commonly appear first on leaves that have been getting plenty of light. When pH is the cause, inner/lower leaves may stay green at first. That’s why leaves in the shade tend to show symptoms later with pH problems. Overwatering can also contribute to pH problems.
The pH at the roots being too high or too low is the most common reason growers see nutrient deficiencies, especially after plants are a few weeks old and the grower is giving nutrients.
Important: Deficiencies in seedlings under 2-3 weeks are usually actually caused by over- or under-watering, not pH.
If you see spots or unhealthy leaves on the slow-growing plant, the first thing to do is check the pH to determine if that might be the root of your problem. It’s possible the pH at the roots is not the same for all your plants despite getting the same conditions and environment.
5.) Natural Variation (Some Plants Are Just Runts)
The fact of the matter is that cannabis plants are living things with natural variation between plants and sometimes it has nothing to do with you. Some plants just tend to grow better than others, while others are runts or duds right from the beginning. In fact, that’s why we recommend to always start more seeds than you plan to grow, so you can choose the strongest and most vibrant plants of the bunch to actually grow out.
Seedlings often vary in size and growth rates even in good conditions.
Each plant has its own “grow personality”. Check out these 33-day old plants germinated together on the same day. All healthy but the front-middle plant is much smaller than the others. That plant started normally but simply grew less fast than the others. It’s common to notice natural variation in your grow even in perfect conditions.
If you’ve covered all your bases, but still have a plant that is much smaller than the others, you have the choice of keeping it or not. If you don’t have extra room and it feels like it’s stealing resources from the other plants, sometimes the best thing you can do is toss the offending runt.
But if you do have the space, it can be worth growing runts out to see what happens. Some plants may not recover, but some plants start growing strong again after they get a little TLC. And there’s nothing wrong with having a plant that’s smaller than the others.
Even smaller plants can produce a lot of great weed!
Jump to…
How to Germinate Cannabis Seeds So They Start Strong
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