cannabis foxtail

What Are “Foxtails” on Cannabis Buds?

by Sirius Fourside

What to Do About Marijuana Foxtailing

Picture some dried and cured, ready-to-smoke 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 ‘weed’.

I’m sure there are a few exceptions, but I’m betting most of you didn’t automatically picture this:

Picture of a cannabis bud with a major “foxtail” coming out the top. In this case, the foxtailing was caused by too much heat, though some types of foxtails are caused by genetics.

There are new green “fox tails” near the top of this cola where the bud is too close to the grow light. On the right is a bud with a typical shape. The lower bud is far enough away from the grow light to be unstressed.

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

So, What Exactly Are Foxtails?

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.

Buds are made up of many calyxes stacked on top of each other, but generally, buds grow evenly and stick together in bunches.

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 plant above. Even the more exotic looking strains tend to form buds with a somewhat even-ish surface:

“Foxtails” are made of several calyxes stacked on top of each other in a tower-like structure.

Even when you can very clearly see each individual calyx (which is natural for some strains), they tend to be relatively symmetric, with a similar amount of “foxtailing” on all sides. (Why are these buds pink and purple?)

Another example of a strain that naturally makes foxtails in normal conditions

Foxtailing buds look a bit different from traditional buds because the 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 strains that grow bud where all (or at least the vast majority) of the calyces turn into foxtails.

Note that on these plants, every calyx is foxtailing….even the calyces on the underside! It appears to be the same action that’s happening in the “bad” foxtailing picture above, but it’s much more complete.

So, is foxtailing a bad thing? It depends…

I know, I know… no one likes an ‘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 you grow cannabis!

The Two Types of Foxtailing
(Good vs Bad)

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 purely a cosmetic issue. However, ‘bad foxtailing’ really is a bad thing and comes with consequences…

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:

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.

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.

Now for the other picture. The other kind of foxtailing (the bad kind) is usually caused by…

Heat/Light Stress
The second cause of foxtailing is environmental and it’s usually caused 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.

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.

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 signs is a message that your lights need to be backed off immediately to halt 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 register as a threat to new growers. 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 the mission is to lose as little as you possibly can.

Luckily, this type of foxtailing is usually localized, so you’ll only see it in spots 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 break these rules, but at least until then you’ll know what you’re dealing with. Good luck and happy growing!

What makes long thin buds grow on top of your regular buds? And when is fox-tailing perfectly normal? Also, why do new white pistils keep appearing on almost-done buds?

What Is Cannabis Foxtailing And What Causes It?

Cannabis foxtailing is a phenomenon in which the buds of a cannabis plant start growing abnormal spires or tips. Read on for an overview of foxtailing, what causes it, and how it can affect your overall harvest.

Whether you’re a rookie grower or a veteran, chances are you’ve heard of foxtailing. But what exactly causes those iconic fox tails to form on your buds? In this article, we take an in-depth look at cannabis foxtailing, its causes, and what you can do to prevent and treat foxtailing in your plants.


Foxtails are a kind of aesthetic deformity we see in cannabis plants. Cannabis flowers, or buds, are formed by a bunch of unfertilized calyces. If pollinated by a male, each one of these calyces could house a seed. When left unfertilized, however, these calyces swell up and eventually form the buds we know and love.

In a normal cannabis bud, these calyces grow close to each other, around the branches of the plant to form round, even nuggets. Foxtails, on the other hand, form when these calyces grow unevenly on top of one another, creating a lop-sided, uneven looking flower.


Foxtailing can be caused either by genetics or by stress. If you’re growing outdoors, any foxtailing is almost always due to genetics. Some strains of cannabis are simply more prone to developing foxtails.

Indoors, however, foxtailing can be caused by light stress during the flowering phase. In this case, plants start developing foxtails in parts of the flowers that are too close to the light source for too long. This is most common in setups with HPS or plasma lighting. Plants with this kind of foxtailing usually also have bleached or burnt tips or buds as a result of the heat from the grow light.


This question is a little complicated. Technically, foxtailing doesn’t affect your buds in a negative way, other than making them look a little odd. However, it’s basically an aesthetic question and some growers even like the look of foxtailing. Others claim that a little foxtailing can help increase your yields, which is always positive.

Unfortunately, some foxtails can get out of hand and form big, long towers on the tip of a flower. While this kind of foxtailing is rare, it can throw off the even distribution of light across the rest of your flowers. This can ultimately affect the flower’s ability to grow and mature properly and may drive down your overall yield.


Foxtails on pure sativa plants are no real cause for alarm as they are often genetic features of this predominantly tropical strain. Sativas with a tropical heritage don’t usually take well to indoor growing and were the bane of early pioneers of growing marijuana under lights. Contemporary lighting technology allows for growing pure sativa strains indoors. However they will still often develop foxtails.

Foxtailing is a quite natural genetic feature in many sativa species when grown outdoors, only the process is more complete. Forming flower clusters with a firm spiky appearance, rather than “running” as can happen indoors. This is why the term “crown” is used to describe main buds, being spiky, like a royal coronet.

To make the most of the pure sativa indoor grow, give them extra attention. They generally don’t like too much feeding, too much nitrogen or too much moisture. Below are some tips that can help prevent foxtailing in sativas:

• The wet dry-cycle can be pushed to the extreme, for example some high mountain Kush strains love dry feet.

• Nitrogen and fertiliser sensitivity is a common feature to sativas. Many growers find that feeding bloom nutrients that are low in nitrogen by nature serve the plant best all throughout its life cycle, even feeding at half to a quarter of recommended dosages.

• Flushing the plant well every 3–4 weeks stops nitrogen and fertiliser build up; then feed it with a PK only nutrient, before going back to the standard routine.

• Avoid growing plants too close to one another, and provide plenty of shoulder room for airflow and light penetration.

• Use a light spectrum that imitates the high UV of the tropics. Sativas can react poorly to the red spectrum of HPS during bloom. Supplement the lighting arrangement with a MH which has a blue biased spectrum, or a blue balanced LED. Using a MH from vegetative stage then through flowering, and not switching in an HPS at all works well with sativas.


When you are sure that the foxtails forming on your crop are not a genetic feature, then there is something wrong with your grow environment. Environmental stresses, such as temperature or light intensity/duration issues, pH imbalances and other root zone stresses can all cause foxtailing. Constant and stable cycles of exactly the same conditions prevent stress in plants and make cannabis thrive indoors.

The first step in addressing foxtail issues should be raising the lights 10cm from their present location. Fully vented HID lamps, HPS or MH should be no closer to the canopy than 58cm. Double ended, uncooled HPS no closer than 76cm and LED no closer than 38cm. With correct light distance, also change the night cycle down to 11–11.5 hours, to help curtail those tails.

Maintain a “lights on” temperature of 23°C and a “lights off” temperature that is 5–7°C cooler. Warmer temperatures can cause stretching, and in the flowering phase this can present itself as foxtail buds.

A healthy root zone is always important no matter what species is being grown, as it is a vector for a number of stresses that may cause foxtails or other issues. Make sure the pH is at a level recommended by the breeder for your particular species. An undesirable pH can cause nutrient uptake problems. Double check that your plants are not root bound. Finally, enable appropriate ventilation, so no stale air forms in the grow room.

Following these tips in both instances should help you grow the sativa you desire with desirable foxtails that form tight spiky buds, or help control undesirable foxtails caused by environmental stresses. Happy growing!

Heard about cannabis foxtailing? In this article we take a quick look at this phenomenon, its causes, and whether it's good or bad for your harvest.