Is low ppfd better for seed development?

Breeder's Lab
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Starting a discussion on seed making/development, based on a recent observation. A fully pollinated Durban Poison (Dutch Passion) was starting to really struggle under high ppfd around week 3 of seed development. I could see that it was being really stressed out.

I took the plant out of the tent and placed it in my living room by the massive windows were they get plenty of light throughout the day. I noticed immediately that the cooler temps and lower ppfd has calmed the plant, and seed development is continuing but at a much faster rate. The plant has stopped focusing energy on producing new growth, which is what it was trying to do under high ppfd conditions. Also, the plant has stopped dropping fan leaves, which was happening at a concerning rate when it was indoors being blasted with high ppfd.

These are my observations. Please share some of your experience and knowledge on this topic. Im really interested in learning more about the optimal (indoor) conditions needed for seed production.

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I treat my regular females the same as my seeded females.

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@Foreigner Can you be more specific about the schedule and conditions?

Ive included data about the change in conditions below.

(Indoors)
Light schedule - 12/12
PPFD - 1100
Rh - 40
Temp - 90F ( summer heat )

(Living room)
Light schedule - Natural Daylight
PPFD - 300-500
Rh - 70
Temp - 70

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Pretty much the same except my humidity indoors is higher and I don’t like to go above 1000 ppfd if it can be avoided.

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Might just be this plant in particular. However, I will be running a more controlled experiment to test my hypothesis :

Is it better for seed development if variables listed below, are reduced on week 3 of seed development. (week 6-7 of flower)

  • light intensity
  • light hours
  • temps
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Yes generalizations of this nature should be taken with a grain of salt.

My last seed run I had two related plants and one started getting sunburnt at about 1000 and the other one grew up into the light and did not give a shit.

Who can say. But I still treat them pretty much the same. Except for harvest processing. With seed plants I just don’t care about the post harvest process.

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@Farmers_Hat
I think it sounds like the plants are extra hungry under the high ppfd, I don’t know how you grow, but I do find in organics it’s really important to give extra top dressing of amendments at a few points to avoid this.

I typically do a top dress about 2 weeks before flower, 1 week in, and 3 weeks in, but if doing seeds I find it helps to add a additional top dress about 4.5-5 weeks in, and increase the amounts a bit.

If growing salts, try bumping up your ppm a bit, start with like 150-250ppm increase and go from there. I also find that seed production requires a bit more nitrogen than normal flowering, not much but a little extra, and extra P and K of course.
Also if it’s a really big plant that’s producing a lot of seeds it might need extra CO2 (even just increased circulation can help) if the ppfd is very high

I do find the timing of pollination can matter too, I try to wait till at least week 3-4 to pollinate, when things are really into flower and there’s a lot of available stigmas

Of course I also think the genetics will play a part too, I think it is possible that both the mother and pollen donor can have an effect on seed growth. The pollen can influence/dictate in some ways how the resources are allocated at the seed level during set and growth of seed embryos.

Interesting thoughts though, I think it would all be proportional to the size of the plant, and the resources available, and the environment.

The vpd can have a dramatic effect on how efficiently a plant can take up and translocate nutrients, so I always look to that first if I feel that everything is good in terms of nutrients

Happy growing, interesting discussion :v::seedling:

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I knock my light intensity back 20%(ish) when I’m running for seed. The plants seem ‘happier’ inasmuch as they aren’t being ‘pushed’ as hard by the lights.

I have a ‘vehicle model’ of weed in my head and the grow lights equate to the throttle response.
The first thing a northern kid learns in winter driving is ‘foot off the accelerator’ at the first sign to trouble. I apply the same rule to cannabis and it has served me well. :wink: :+1:

Cheers
G

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Damn that makes sense @Gpaw !!!

:raised_hand_with_fingers_splayed:

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Thanks fellas. Those are some helpful tips.

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I run lower light intensity normally anyway 700ppfd max. You can grow quality flower at 300 ppfd if theres light penetration and airflow. 1100ppfd, and you better have all other parameters in check for healthy growth or you will have significant light intensity stress.

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I think that’s how I hermed my strawberry cough. Wayyyy too much light.

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I suspect the same thing is true for both of my F3 Valley Ice cuts. They threw sterile bananas, most likely from too much light. Outdoors they grew normal.

I should probably upgrade my set up. I won a Phlizon FD6000 earlier in the year. A giveaway on RIU forum. I need a 4x4 tent for that light. That light has a dimmer, which would be super useful. My current lights dont have dimmers. Im running 2 VS1000E lights in a 2x2.

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Dimmers good.

Rapid LED is having a sale this weekend for all the DIYers out there. 15% off code LABORDAY25 and free shipping in US. I prefer LED strips and Digikey has decent prices on the Bridgelux EB strips.

I’m jonesing to build another LED fixture.

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90F is pretty damn hot for most plants. Equatorial sativas are another story, but for most grows…

They may have been happier with the lower temp rather than the amount of light. Although 1100ppfd is pretty high without adding supplemental CO₂.

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I can’t say which is better, but I can say they don’t a whole lot of light to make beans. I make most of mine in a greenhouse over the winter without any supplemental lighting. Low sun angle, lots of cloudy and short days, as low as 9:45 hours of daylight. They stretch a bit, but there’s always tons of beans. :man_shrugging:

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It might be more useful to frame the lighting question in terms of DLI rather than PPFD.

I dim my lights on seeded plants on the theory that most seeds mature in the Fall when the daily total light energy is dropping and the plant is drying out naturally.

DLI (Daily Light Integral) is a measure of the total photon flood that the plant receives over a 24 hour period. During flowering, you are already on a reduced lighting schedule, maybe 12/12, but you could reduce PPFD OR reduce the hours of “Daylight” even further to decrease DLI.

A seeded plant is headed for senescence and die-back so she will look increasingly sad no matter what you do.

But you guys already know this, right?

Grouchy :v: :green_heart:
PS, take a look at the PhoTone app for an inexpensive way to measure PPFD & DLI using your phone…

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I agree that 1100 ppfd will demand extra CO2, and that could be the main stress.

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Just keep your plants happy and don’t overthink it…
I usually run a little bit more N, and I don’t flush when running for seeds :smiling_face:

Pz :v:t2:

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On the topic of fertilizers, this plant was well fed. Actually, overfed. So the fan leaves falling off is more likely from senescence or heat stress. 90f doesn’t seem to be affecting the other plants. Right now I have managed to keep the temps around 84f.

In regards to CO2, the tent is partially open and I have fresh cool air from outside being blown into the room. I imagine there is adequate CO2 in the cool night air. Lights dont go on until 9pm.

I think this plant was struggling because of DLI and PPFD. She must be a little more sensitive. I was beginning to think that maybe the roots were rotting, but she looks a lot more relaxed under the new conditions in the living room. She should be able to finish off without any issues now.

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