What causes foxtailing in cannabis? Is it strain related or are foxtails caused by other factors like too much light or heat. I experience foxtailing on some strains so I wanted to find out how to fix foxtailing buds. Can you reverse foxtailing or is it genetic and can it be caused by too much light or the spectrum of light used.
Here is a picture of some Double Tap a strain from Solfire Gardens which is a cross of GG4 and Black Banana on day 56. She definitely has major foxtails. You can see the calyx is built from one bud stacking on top of another.
Some people dislike foxtails and say they are bad but I happen to like the look of this bud. There are good and bad foxtails too. These calyxes are elongated but they are solid. The bad kind is wispy and not dense and in some severe cases the entire bud can just be white hairs that never really fatten up.
Some strains seem to have a genetic predisposition to foxtailing. This is a natural trait in many sativa strains and many strains we grow have sativa genetics in them.
For example in the strain GG4 AKA Gorilla Glue foxtailing is fairly common. Let’s have a look at the genetics in this girl. Gorilla Glue #4 is a mostly sativa variety and a cross of Sour Dubb x Chem Sis. You can check out the full genetics line at https://en.seedfinder.eu/strain-info/Gorilla_Glue_4/Unknown_or_Legendary/
A quick look at the genetics shows Hawaiian and Chocolate Thai in the genetics which are sativa dominant. There is also Skunk in the genetics which carries sativa genetics too. In fact Thai is known to foxtail naturally. So with a genetic mash up like GG4 has it should really be no surprise to see foxtails show up in this strain.
Does The Grow Room Environment Cause Foxtails?
If you look online you will see that too much light or high temperatures are the most common causes given for foxtailing. I think this is responsible for the bad type of foxtails but I think genetics or other factors are also responsible for causing this.
As far as heat goes HPS should be run at about 75 and LED at about 80-82. LEDs dont give off radiant heat like HPS lights do so they require a higher temperature for photosynthesis. However that certainly is not excessive for cannabis and temps for both can actually be raised when CO2 is added.
Light intensity is cited as another common reason for foxtailing. With HPS high light intensity usually goes along with high heat and symptoms like tacoing or leaf burn will often show up too.
But with LED lights there is much less heat so it is very easy to over saturate your plants. You normally wont see burning but you may see bleaching especially at bud tips. There can be tacoing or leaf rolling and also leaves can be yellow or look like they have a nutrient deficiency.
However in my case my temperatures are in check and I check my light levels with a par meter. I try to keep my levels between 500-800 but occasionally some taller colas can get a bit more. Lower buds on my plants that get less light still have foxtailing although it may be less.
Light Spectrum – Do LEDs Cause Foxtailing?
I grow with LEDs and I use COBs and Quantum Boards and yes I do get foxtailing on some strains and none on others. Both Tropicanna Cookies and the Double Tap shown above grow very similar bud shapes and both have a good amount of sativa genetics in them.
However, I know growers with the exact same cut of Tropicanna who dont get those elongated buds. Theirs are chunkier and more “normal” looking. But they are growing with HPS lighting. So is there something about LEDs that causes foxtails?
You can check out this grow journal at https://420grower.org/animal-cookies-in-new-sip-grow/ Although this Double Tap has foxtails it is neither too hot nor is it getting too much light. In fact I needed to add a small heater to get the temps to 81 and it has a par reading on top around 400 and the lowers are only about 200.
Then in this case it is not caused by too much light or high temperatures. This leads me to believe it is genetic and the COBs are allowing it to express itself.
Light Spectrum And Bud Shape
So this also brings up the question of what is normal. HPS is a very incomplete spectrum with very little blue light in it at all. It is about as far as you can get from natural sunlight but it works very well for flowering.
Sunlight has a kelvin temperature of about 5000 degrees with a CRI (color rendering index ) of 100 while HPS is around 2200k. It also has a very low CRI of 22 so colors are not rendered very well.
Given the differences in spectrum it should not be surprising if plants grow and flower differently. So is a HPS flower normal or are we just used to it because they happen to be the predominant spectrum most growers use? I dont grow outdoors but I would guess the flowers in sunlight are different and probably have more foxtails.
LED lighting is a different animal entirely and a cross between the 2. My COBs are rated at 3500k and my HLG 550 quantum board is 3000k. Both have a high CRI of about 90.
I would have to conclude that LED lighting allows foxtailing to occur if it is in the plants genetics because it is closer to the suns full spectrum and HPS does not do this because it is a much narrower and more red based spectrum.
How To Fix Foxtailing Buds?
Unfortunately I dont have an easy answer for this. I am not about to switch back to HPS lighting. I am a closet grower and dealing with the extra heat is difficult and so is looking at my electric bill. My power bill is half what it was and my yields are the same so at least for me it is not an option.
In most cases high temperature and too much light are the cause of foxtailing so the obvious fix is to adjust your environment accordingly.
Make sure your HPS lights are not too close. If using HPS make sure your buds are not getting too close to your light. Check leaf surface temperature with a temperature gun. They are cheap insurance. You can not go by room temperature.
LEDs are a bit trickier because they dont give off enough heat to burn your plants. This makes it very easy to have them too close. Ideally you want to use a par meter to check the height. There really is no other definitive way to know if they are getting too much light and using manufacturer guidelines may not be right for your situation.
Daily Light Integral Possible Fix
I can not change the spectrum of my lighting nor do I want to. I believe the closer we can get to sun light the better our grows will be. Plants have spent millions of years evolving and growing under the sun. The main advantage of indoor growing is really climate control not better lighting.
Daily Light Integral or DLI may have potential to help stop foxtailing. It is a formula used by greenhouse growers to determine how much supplemental lighting to use. Plants have different light needs. Cannabis and tomatoes for example have high light requirements. But as these photons accumulate during the day it is possible for a plant to receive more light than it needs or can use.
What DLI does is determine how long they need that intensity. So it is possible with high power LEDs, especially the white light ones, the length of intensity might be too long and encourage foxtailing. Perhaps running 11 on and 13 off would help.
I have not tried this so it is just a theory. Personally I dont have a problem with good foxtailing and in fact I really like the look.
Do LEDs Cause Foxtailing? Experimental HPS Test Grow
Sometimes something just bugs me and I want to find the answer and solution to my problem. So I decided to do a test grow and find out if my lights are causing plants to foxtail or if there are other causes.
I have 4 strains that I am familiar with and have grown multiple times. Two of them, Tropicanna Cookies and GG4 always foxtail under my COBs and quantum boards.
So I took down my HLG 550 and swapped it for a 600w HPS. The plants were only 7 days into flower when the change was made. By the end of this grow I should know if lighting is the cause or if other factors are in play.
1000w HPS Upgrade
The 600w HPS I was running was not really giving me the coverage I needed so I pulled out an and hung it with a
Hoping the light switch does the trick. Everything looks happy and temperatures have stayed around 76-78 degrees. With the air cooled hood temperatures are lower running a 1000w bulb than running the with a 600 watt bulb.
SIP Planter To Drain To Waste Conversion
I have decided to change my growing system from a sub irrigated planter to a DTW top feed drip system. Many people say you can’t recirculate coco. I have done it in the past but at this point I am having issues with dropping pH and until I figure out a work around I need a system with proven results.
I like to automate when possible and although hand watering is effective it can be problematic lifting pots under a trellis. Since I already have a drip system that is what I will be using. Canna recommends DTW and advises against recirculating in coco. So that is what I am going to do.
There are the same 4 plants under the same 1000w HPS and the plants sit on top of seed flats because I want them to drain freely. I want air space under the smart posts. The plan is to water 3 times during lights on for 15-30 seconds. Water will be held in the flood tray and pumped out into a bucket for disposal because I do not have a drain nearby.
Drain To Waste – Not That Wasteful
After running my pump 15 seconds I collected about 10 ounces of liquid from two drip lines. There are 2 per pot so I will go through 40 ounces every watering or 120 ounces a day. That is a bit less than a gallon.
Because my reservoir is filled with 20 gallons of nutrients it should last almost 3 weeks. I would actually use more nutrients recirculating if I changed my reservoir every 2 weeks. So maybe drain to waste really is not that wasteful.
The Advantage Of A Drain To Waste System
The main advantage of this system is stability. Your nutes are always the same every feeding unlike a recirculating system. This can help prevent over feeding and nutrient lock outs. When you recirculate plants take out different nutrients at different times so your reservoir can easily get out of balance.
One thing that can cause foxtailing is excess N or too high a nutrient level. So I am hoping the change in lighting and the change in my grow system will result in fewer foxtails.