If Your Cannabis Plant Looks Stunted, You May Have A Runt: Here’s How To Tell

Runts are the bane of many cannabis cultivators, often costing them resources while not being able to deliver the kind of quality one expects. Runts exist within all areas of agriculture and aren’t limited to cannabis, but given the time-sensitive nature of cannabis crops, a runt can often be very disruptive to the growth, sometimes being better off culled.

In this article, I’ll guide you through what causes runts, how to minimize the odds of having one in your grow room, and why these plants are often culled rather than grown through to harvest.

Key Takeaways:

• Runts can be influenced by genetics and human error.
• Autoflowers are more prone to have runts.
• It may be better to cull autoflower runts, saving time and money.
• Runts are a normal part of the growing process and occur in 10 to 20% of seeds.

What Is A Runt In Cannabis Cultivation

A runt is a plant that doesn’t develop at the same speed, or with the same vigor as normal plants. They are often very small and may also show signs of mutated growth in some cases.

What causes a runt varies but can stem from genetics, soil condition, and even watering practices, to name just a few reasons why they occur.

How To Tell If You Have a Runt

So how do you know if your plant is a runt or just a little on the slow side?

There’s no conclusive definition that separates them, but for the most part, runts take longer to recover than those that are just a bit slower in their growth. Still, even just a temporary slowdown is easily noticeable in the final results of autoflowers.

If you planted several seeds at the same time and one is lagging significantly behind, and this lasts out of their seedling phase, chances are you’re dealing with a runt.

Runts Are Fairly Common

Growers who germinate large volumes of cannabis seeds have become used to seeing runts show up. It becomes mandatory in these large germinations to weed out the weak plants early on. But for those only germinating a few seeds each year, it may take some time before they run into their first runt.

Here’s how common runts are…

Photoperiod Seeds (~5-15%)

Normal cannabis seeds have around a 1 in 10 chance of being a runt. These weaker seedlings can often be nurtured, and over time recover from their inherent weaknesses. But it does take time.

Autoflowers (~10-25%)

Autoflowers are more prone to runt problems, both because of their fixed life cycle and the way they grow, being more vulnerable to small stresses. Once stunted, it is often nearly impossible to get these plants to produce a normal harvest.

That’s because they can begin to enter the flowering phase while still in their stunted phase, without the time required to grow out of it.

It’s essential to provide the best possible growing environment to your autoflowers, right from the start. This will help reduce the number of stunted plants.

Clones (~1-5%)

It’s not only seeds that can be runts, clones that were taken when the plant was too small, or clones with damaged roots can also become stunted, but these tend to be easier to grow out of with sufficient care.

Environmental Stress & Human Error (~10-20%)

Even strong genetics can become runts if the growth conditions aren’t right. Up to 20% of runts occur because of human error. This includes things like damaging the roots during transplant, improper watering techniques, or even issues with the nutrients being provided.

Runts May Be Genetic, Or A Result Of Stress

It would be incorrect to assume all runts are the result of genetic problems, although that is a leading cause. Other causes include:

• Nutrient deficiencies
• Too much or too little water causing stress
• Pests
• Growing multiple plants in the same container
• Cold temperatures

These are just a few issues that can cause plants to show stunted growth and be considered runts.

Why Runts Suck For Autoflower Growers

Runts are pretty common in cannabis seeds, and if you pop enough seeds, chances are you’re going to encounter one sooner rather than later. For growers running photoperiod seeds, runts can sometimes be given time and nurtured to the point where they can catch up with other plants in your grow area. However, the same is not true for autoflowers.

Autoflowers have limited veg time before they enter into flower. On average, an autoflower cannabis strain will begin to flower in between 14 and 30 days of vegetative growth, meaning there’s not a lot of room for error.

If your autoflower is still small after 2 weeks of growth, it’s a real problem as it’s unlikely it will ever produce enough flower to warrant keeping it around, and sometimes it’s better to simply write it off.

Should Runts Be Culled?

Culling runts is a common practice for growers looking through large amounts of plants, where only the strongest survive. But if you’re a home grower who’s just bought a small pack of seeds, letting go of one of your babies can be difficult. There’s a part of you that just wants to keep trying.

So should you remove them?

That depends on whether they are autoflowers or not, and how badly stunted they are.

If you find an autoflower runt that begins flowering while stunted, it’s often better to cut your losses and pop another seed. Think of it this way, planting a healthy seed can easily grow bigger than the runt in just a couple weeks.

For photoperiod plants, I recommend being a bit more lenient and giving it time. I’ve had dozens of runts over the years that when given time and taken care of, went on to produce amazing flowers. I’d personally recommend waiting until these plants are big enough to clone and then replacing the original plant with the rooted clone.

This helps combat the inherently small roots that tend to be found on these runts.

But even with photoperiod plants, there’s sometimes a point at which it’s easier to just let it go. Only you can make that decision though.

How To Minimize The Risk Of Runts

There are two ways to approach minimizing the amount of runts you encounter, and implementing both methods is typically the best approach.

Choose high-quality seeds, which have better quality control will give you slightly better odds, as great breeders will often do their own internal testing before releasing a strain. Budget white-label seeds are less likely to go through these checks.

Protect the roots when planting or repotting.

Plant each seed in different pots to avoid roots from becoming bound within each other or one plant dominating the other.

Avoid excess watering or dry-backs, which can stress the plant, especially autoflowers.

Ensure correct feeding to avoid nutrient lockout.