Potassium or more?

T

Tedmarx38

Well-Known Member
Friends, I flushed these a week ago and added back nutes the next day. The slurry test yesterday for nitrogen and phosphorous show slightly deficient but potash/potassium (k) was severely deficient.

I’m using the FoxFarms bundle of Big Bloom, Grow Big and Tiger Bloom liquids plus their three low dose powder boosters as per their week x week schedule. Yesterday I did, however, double the Beastie Bloom booster (high in k) by using 1/2 tsp instead of 1/4.

Specifics below but I’ve had this problem before during flowering and as noted my spring water is very close to RO although very alkaline.

My questions: does this look solely like a K deficiency or is something else wrong? And, if it is just K, since it keeps happening should I continue to exceed recommended dosing of that element? (Only the rightmost of these four shows considerable damage but the others show early signs of it too.)

Thanks as always

Details:

Four sativa-dominant photoperiods from seed.
Week 6 of flowering.
2x4 tent is 75 degrees 35% rh
12/12 light schedule
Spyder sf 2000 led 200 watt
Lumens - 50,000
Fox farms ocean forest soil
Alkaline spring water with high ph and low tds.
Watering/feeding at ph 6.3 and using one tsp calmag and 1/4 tsp epsom with feedings along with FF’s recommended nutes by week

IMG_1459.jpeg
 
Your tent is a bit cool. Optimal ‘lights on’ temp would 84f for nutrient uptake with LED lights. You can google cannabis Leaf surface Temperature (LST) using LED lighting.
 
Tedmarx38 said:
Friends, I flushed these a week ago and added back nutes the next day. The slurry test yesterday for nitrogen and phosphorous show slightly deficient but potash/potassium (k) was severely deficient.

I’m using the FoxFarms bundle of Big Bloom, Grow Big and Tiger Bloom liquids plus their three low dose powder boosters as per their week x week schedule. Yesterday I did, however, double the Beastie Bloom booster (high in k) by using 1/2 tsp instead of 1/4.

Specifics below but I’ve had this problem before during flowering and as noted my spring water is very close to RO although very alkaline.

My questions: does this look solely like a K deficiency or is something else wrong? And, if it is just K, since it keeps happening should I continue to exceed recommended dosing of that element? (Only the rightmost of these four shows considerable damage but the others show early signs of it too.)

Thanks as always

Details:

Four sativa-dominant photoperiods from seed.
Week 6 of flowering.
2x4 tent is 75 degrees 35% rh
12/12 light schedule
Spyder sf 2000 led 200 watt
Lumens - 50,000
Fox farms ocean forest soil
Alkaline spring water with high ph and low tds.
Watering/feeding at ph 6.3 and using one tsp calmag and 1/4 tsp epsom with feedings along with FF’s recommended nutes by week

IMG_1459.jpeg
Click to expand...
 
You're experiencing K def because you seem to have the "kitchen sink approach" when less is more growing Cannabis? 1/4 tsp Epsom sounds way to hot to add to a already complete plant food? Epsom on top of beastie blooms and even more boosters on top of that? This approach is why you experience problems.

There's no point in force feeding the plant when the only result is nutrient toxicity.
 
The plants look good compared to some that we have seen here when others have used the same soil, fertilizers and water with a pH of 6.3. Way to often we have people post msgs asking for help in their 2nd or 3rd week of flowering because they have a lot more of their leaves turning yellow to brown and falling off.

You might be needing a bit more Nitrogen and along with some Potassium but since the plants have already been flowering for 6 weeks plus I doubt that there will be enough time to have a noticeable change.

@Wastei mentioned the Epsom Salts which are good for supplying magnesium and sulfur. I doubt that you need either of those in the current grow.

As for the Fox Farm fertilizing schedule are you using the one from their website? The reason I am asking is that yesterday evening I was looking at copies of Fox Farm schedules found on several other msg boards and on the web sites for various businesses selling the fertilizers direct and through Amazon. Most of those web sites had older schedules with lower doses of the Fox Farm Trio and a less frequent feeding.
 
SmokingWings said:
The plants look good compared to some that we have seen here when others have used the same soil, fertilizers and water with a pH of 6.3. Way to often we have people post msgs asking for help in their 2nd or 3rd week of flowering because they have a lot more of their leaves turning yellow to brown and falling off.

You might be needing a bit more Nitrogen and along with some Potassium but since the plants have already been flowering for 6 weeks plus I doubt that there will be enough time to have a noticeable change.

@Wastei mentioned the Epsom Salts which are good for supplying magnesium and sulfur. I doubt that you need either of those in the current grow.

As for the Fox Farm fertilizing schedule are you using the one from their website? The reason I am asking is that yesterday evening I was looking at copies of Fox Farm schedules found on several other msg boards and on the web sites for various businesses selling the fertilizers direct and through Amazon. Most of those web sites had older schedules with lower doses of the Fox Farm Trio and a less frequent feeding.
Click to expand...
Is it just my UK perspective or do we see a lot of problems with Forest and Frog 'soil' SW?
 
Tedmarx38 said:
Anyone else finding that there are fewer comments on their posts lately? Starting to get paranoid….
Click to expand...
I noticed that there are fewer new growers coming around. The old guard is still here judging by the participation in the journals. But, first or second time growers are not around as much and I am not seeing as many posts from people just getting started.

Here in Michigan the price of Cannabis buds/flowers has dropped so low that it is worth it for smokers to go the dispensaries instead of investing several hundred dollars in tents and lights plus the monthly cost of electricity and the time involved. I am pretty sure that some of the other states are similar.

Even long time underground growers are shutting down because they cannot continue to pay their expenses if they try to match or beat the legal market prices. Just heard about another one over the weekend. He just shut his basement down and told his regular customers that their was no way for him to keep going if he was loosing money on every plant.
 
Roy Growin said:
Is it just my UK perspective or do we see a lot of problems with Forest and Frog 'soil' SW?
Click to expand...
No. It is inexperience when growers are trying to get to much out of the soils in 3 and even 5 gallon pots. They try for the largest plant possible which means that it is growing for more than 4 weeks and even if it did not go into flowering they are already starting to push what the root system can do.

Then a lot of them are uncertain about how much fertilizers to use so they go too light which does not help. They are often looking for hydro results without using the same quantities and exact measurements that hydro needs. They are trying to grow a bumper crop using houseplant methods.
 
Interesting, it's still underground over here and people are willing to pay whatever for quality bud if they can get it - nobody wants cheap shitty bud, so you need to know a grower
 
Thanks all for the insight. I was using Epsom based on a reco for it as a sulphur source. I’ll cut back on it in my early stage grow. Re Fox Farms, the table I’m using with it came in the shipment about a six months ago. I’ll check for newer ones. It always seemed a bit stout to me and has other products listed and recommended for addition that I don’t purchase. As for the mixture being too robust, I think my source water is so bland that it needs a lot of love. Each soil slurry test I’ve done over the 8 indoor grows I’ve completed shows deficiencies and never excess amounts. I sure do appreciate all comments and insights.
 
Roy Growin said:
Interesting, it's still underground over here and people are willing to pay whatever for quality bud if they can get it - nobody wants cheap shitty bud, so you need to know a grower
Click to expand...
I believe that it is a case of the quality of the flower has met the price being asked. Or, the price of the flower on the shelf has dropped enough to meet what the public wants to pay for the quality.

Even as the wholesale prices dropped the licensed commercial growers could not let the quality drop, for what it was. So they kept producing the same quality, had to keep sending it in for testing, etc. but they had to accept less for their time, wages paid and other expenses.
 
You are adding cal mag and epsom salt? Epsom salt is high in magnesium. High levels of Magnesium blocks the plants ability to absorb Potassium. Lower/older leaves yellowing back with the base and vein turning yellow last is potassium def or lock out.
You are on the low side of temp depending on the strain mix. Not enough to harm, just slow down growth.
Have you tested your run off PH?
 
Cannabis grows well in a the 70's or 80's. Were I able to control temps in the garage in which my grow tent (2' x 4') is located, I'd set it and forget it at 80°. Temperature does impact the crop but there are a slew of other factors that work in concert (or don't work in concert) to get an excellent grow.

Rather than arm wrestle over the "optimal" temperature and humidity, a more sound approach is to use vapor pressure deficit. Your 75° ambient temp will work well for cannabis but 75° + 35%RH is, in a world, brutal.

This is the best single source I've found for understanding VPD. If you haven't delved into it, it's a great way to get two of the growth parameters in check.

Parameters of Growth.png



At 75°, your humidity should be about double to get your plant into a healthy range. In the current conditions, your plants are under significant stress - even though the temperature is mild, the combination of temperature and RH is so dry/warm that the transpiration rates are very high. You'll have to add a lot of water and you can expect nutrient imbalances to continue until you bring VPD into range.

Your light levels are below the light saturation point (800-1000µmols). Your PPFD is in the 770µmols range which is better than most but below optimal. When you get the VPD issue resolved, you might be able to boost your light levels so your plants can produce more food. Crop quality and yield increase in an almost linear manner as DLI increases so don't be afraid to turn it up once you get the temp + RH nailed down.

My thinking:
1-get smart on VPD
2-get an IR thermometer so you can get the leaf surface temp and then get your temp + RH set so your VPD is in range.
3-go back to basics on nutes. The amount of dissolved solids in your water needs to be taken into account when mixing nutes.
4-Adding Epsom + Cal/Mag — re-examine, one, the need for these and, two, how to determine the amounts that are needed. Sure, we can add chemicals but it works out better if you determine which specific chemicals are needed and exactly how much of each one is needed.
 
Back
Top Bottom