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What Are Foxtails?

by Sirius Fourside

Picture some dried and cured, ready-to-smoke/vape bud in your mind. Maybe it’s some you’ve harvested yourself, maybe it’s some exotic-looking unique strain, or maybe it’s just a generic picture your mind pulls up when you think ‘bud’.

Although I’m sure there are some exceptions, I’m betting most of you didn’t automatically think of bud that looks like this:

This picture is the definition of (one type) of foxtailing!

We tend to think of buds as having an oblong shape with a pretty much even surface like this:

The classic conical bud shape!
Many auto-trimming machines cut off foxtails, so if you used to purchase cannabis regularly you may have bought buds with foxtails without knowing. That’s not necessarily a bad thing, though!

The bud we know and love is made up of a bunch of calyces (that’s the plural for ‘calyx’) and each calyx is a potential home for a seed. However, those seeds will only develop in cases where pollination or hermaphroditism (developing both male and female sex organs) occurs. 

As female cannabis plants mature and soak up light, they grow calyces in groups which pile up on each other until they end up looking something like the bud above. Even the more exotic looking strains tend to form buds with a somewhat flat-ish surface:

Why, aren't you exotic looking?

What makes a ‘foxtailing’ bud different is that the bud has parts where calyces grow on top of each other to form spires. These spires/towers throw off the overall shape of the bud as we’re used to, so they look odd to most people. However, there are also plants that grow buds where all (or the vast majority) of the calyces foxtail. A good example is this cole train pictured below:

Cole train knows how to foxtail!

Note that on this plant, every calyx on the bud is foxtailing...even the calyces on the underside of the bud! It appears to be the same action that’s happening to the bud in the first picture, but it’s much more complete.

So, is foxtailing a bad thing? It depends…

I know, I one likes a ‘it depends’ answer. A ‘yes’ or ‘no’ would be a definitive answer and it feels so nice to feel like you know something for sure! Luckily for us as growers, you can learn to tell if the foxtailing you’re seeing is good or bad in just a few minutes! Now you can impress your friends!

Note: That was a trick! Impress your friends with cooking and/or Karate, but tell no one if you grow cannabis!


The Two Types of Foxtailing
(Good vs Bad)

Wait, two types? Two types means there are only two choices...and two choices means...this pretty much IS a ‘yes’ or ‘no’ question to the trained eye!

Before we go any further, I have to admit that designating one type of foxtailing ‘good’ is a bit misleading. I call it ‘good’ in that it doesn’t provide any positive or negative benefits; ‘good’ foxtailing looks a bit funky but ultimately it’s a cosmetic thing. I also call it ‘good’ foxtailing because ‘bad’ foxtailing actually does have negative aspects.

Being able to tell if the foxtailing you’re experiencing is good or bad is as simple as being able to tell the difference between two foxtailing pictures. Here are two more examples side-by-side:

An easy-to-compare picture with the two types of foxtailing

Let’s start with the one on the left. This type of foxtailing is caused by:


Some strains of cannabis have been bred - by humans and/or mother nature - to form buds where foxtailing is the norm. Although often foxtailing is caused by heat or light stress, when you’re growing a strain that is genetically predisposed to foxtail, the whole bud joins in on the foxtailing action. This makes it so that genetic foxtailing looks more uniform than the other type of foxtailing we’ll review in a minute.Dr. Grinspoon is a weird-looking form of foxtailing, but it makes good cannabis!

The picture to the right is a strain called ‘Dr. Grinspoon’ (named for the esteemed cannabis activist, Dr. Lester Grinspoon). The look of this plant could be considered another manifestation of genetic foxtailing, and it’s important to note that this action happens everywhere on the plant.

Good or Bad? In short, there’s nothing wrong with genetic foxtailing. The fact that it’s genetic means that it was going to do it regardless of whatever specific growing technique is being used. These strains are also capable of containing high amounts of THC, so it doesn’t seem that genetic foxtailing reduces the potency of the plant.

This type of foxtailing is the good type. Again, that only means that it’s good by comparison to bad foxtailing in that it doesn’t cause any negative effects.


Heat/Light Stress
The second cause of foxtailing is environmental and it’s usually cause by your lights. If you’ve ever parked a high-powered HPS or LED light (CFLs and T5s aren’t usually strong enough) too close to your cannabis, you might see it grow these odd spires.

A almost pleasant looking, but definitely bad manifestation of foxtails...

A strong foxtail spire caused by light stress!

The fact that the foxtails only seem to appear at the top means this is a bad thing...

What about when buds keep growing new white pistils over and over? This is another version of foxtailing that is caused by heat and light stress. If it's only happening to the parts of the plant closest to the light, that's a sign that it's being caused by stress instead of genetics.

Example of heat and light stress - the extensive new growth at the top of the bud is caused by the grow light being too close!

Good or Bad? Bad! This type of foxtailing is a sign that your buds are getting too much light and/or too much heat! These odd spires can also be accompanied by light bleaching and cooked leaves. Any one of these three signs is a message that your lights need to be backed off immediately to stave off any further damage. Although light bleaching and burned leaves are obviously damaged, foxtails don’t look damaged so much as they just look weird so they don’t seem to be a threat. Unfortunately they’re the harbingers of heat damage which means lost potency; if you see this type of foxtails on your buds, you’ve likely already lost potency to heat and now it’s a race to lose as little as you possibly can.

Luckily, this type of foxtailing is normally localized, so you’ll only see it in spot where light intensity is super-high. This usually means they’ll be found in a small circle directly under the light, but that small circle gets larger as the light gets closer.

Now with all that being said, plants are weird! It’s totally possible that many of you growers have already seen a plant that makes the ‘bad’ looking foxtails but all over the plant. Or maybe a plant that only grows in spires! The point is that there is bound to be plants that breaks these rules, but at least until then you’ll know what you’re dealing with. Good luck and happy growing!

Learn more about why some plants keep growing new pistils on top of their buds



Jump to...

PSA: Too Much Light?!

How to Use a Cheap Lux Meter to Increase Yields

Cannabis Light Burn

How to Prevent and Treat Heat Stress