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Foliar feeding, friend or foe?

What are your opinions on foliar feeding/spraying? Does it work, or is it a crock?

Frequency? Time of Day?

What nutrient deficiencies do you think is best to try and correct through foliar spraying? Are there any nutrient deficiencies that you believe to be useless to try and fix through foliar spraying due to mobility of the nutrient or any other reason?

Are there other products that you apply through foliar spraying that isn’t necessarily to try and fix a nutrient deficiency? for example, do you spray anything to improve the health of the plant, like Aloe to prevent pests from being attracted to your plants…

Do you spray regularly, or only as needed when you see signs of deficiencies? Do you spray only on clones, or only in veg or bloom?

And do you rinse your plants afterwards to prevent buildup on the foliage?

Thank you all in advance!

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We use a number of different foliage applications - activated mild compost teas for nutrient uptake (plants will take up a % of nutrients through their leaf structures), for pesticide defense (for eg. something with a high silica content - maybe a horsetail supplemented tea) will create a stronger barrier on the leaf and deter a number of pests, a capsaican (hot pepper) tea to deter insects, you can even use a fresh milk solution that can help defend against botrytis and other molds.

Foliar teas are better as a supplement rather than a fix to nutrient issues as plants will not absorb as many nutrients through their leaves etc than their roots.

Best not to spray in the later stages of blooming.

Morning or early in the light cycle is best.

We generally do a water spray 24 hours after to wash any heavy residue off.

If you spray clones or seedlings, dilute the mix further than you would for larger plants. As you would for general fertilizer application.

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Nitrogen deficiency can be corrected with a foliar application, but other nutrients can’t. For the most part, plants are made to absorb nutrients more efficiently through their roots.

Silicon like from our Pro-TeKt is a great preventative, but much more effective if absorbed by the roots. Silicon is taken up by the plant and deposited in the cell walls. It has to be fed continuously during the plant life cycle because silicon does not translocate within the plant once it sets in place. Regular applications of Pro-TeKt will help prevent powdery mildew and make it harder for insects to feed off the plant.

Another good preventative is the use of Neem Oil. Neem will reduce the incidence of spider mite, for example. It is not recommended to be sprayed on finishing buds.

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Bumping this topic for the newer folks.

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I use the VEG+BLOOM nutrient line, and it comes with a foliar spray called PUSH, which is basically Calcium. It is recommended to spray on the plants during their vegetative state twice a week and first 2 weeks of flower, every 5 days.

This foliar spray is okay to use with lights on or off, however we use it an hour or two before the grow lights come on. The temperatures are cooler during this time and gives some time for the moisture to evaporate before the intense lights kick on.

I don’t notice much of a difference using it and not using it. I can’t say it helps, but I can say it DOES help during transitions from veg lights like T5s or LEC to HPS or increased heat. I have noticed reduced shock time when spraying every other day for the first week of transition from veg to flower.

Does anyone find that one nutrient works better than others when spraying a foliar?

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I have never had good results from foliar with chemical fertilizers. I had tried in the passed and never used them again. I had heard good results from others. But also IMO when growing “synthetic” one really doesn’t want to increase wet time on foliage. The Plant in that system will have less tolerance/defense capabilities to fight incoming spores.

Recently(in the last year) I started using aerated compost teas. With thermal compost as the catalyst. (Also earth worm casting and adding various ingredients from there. But simple. Only one or two per brew after the composts)

There is studies being done currently around the topic of these teas suppressing powdery mildews or in the least as a preventative treatment.
The findings I heard was that it changes the surface conditions of the leaf and fills its with microbiology that will fight off or eat or out compete the spores from fungal pathogens.

Long story short I tried this one my tomatoes last summer which had blight on them already. (I grow them vertical vines in 20-50 gallon containers) mulch+compost+promix base soil
(Started season with chemicals. Drove them into deficiencies and ph problems, couple weeks hybrid, then switched 100% to compost, AACT, and the results are amazing. Plants corrected problems with ph automatically. (Tea reads 8.0 ish)
Yields increased. More flowers per cluster etc.
not to mention the plants that were foliar sprayed regularly still grew after a few frosts. (New flower clusters after a frost, with minimal damage to flower, unlike damaged flowers from rain in summer? During chemical growth)

In terms of how often. I commonly water every water with some kind of aerated tea.
Base with earth worm castings or compost.
Add kelp meal or alfalfa etc. but keep it simple. We need the microbiology not the ingredients.

I sprayed the tomatoes foliage up to everyday, in the heat of 33*c at 2pm. Just to see what could go wrong. It doesn’t. As long as the tea is aerobic and done correctly. It only helps the Plant.

Some heavy alfalfa teas can burn foliage. (On a sumac and hydrangea) raspberries really didn’t like the heavy bacterial teas or soils created from it.

For the cannabis I use the AActs up till mid flowering or when the flowers are starting to get dense and there’s a chance that proper drying may not occur.
If I got a problem I would spray farther if needed.
Treating the soil does take a while (10-12 days I’ve read?)

I’ve heard on some podcasts that if teas are applied to late then the microbial testing can be affected. This applies also for organic food production.

Based on dr Elaine inghams research this is not applicable to soil web grown bioculture as much as some bacteria in anaeraboic conditions.

Always try to spray foliage with the longest drying time possible after. And if possible not in the direct heat or intense light.
Otherwise spray just before lights on and have good air movement always.
Using things like aloe in the tea will allow everything to stick better to plant surfaces.

“Surfactant” is what we added to chemical sprays.

Coverage is the most important thing.

Nitrogen seems to be improved very quickly with alfalfa. I’m reading into the benefits of kelp meals, diataceous earth(silica), plant teas etc.
Molasses has some things as well. In terms of uptake in mineral form I’m not sure through foliage. I use it for defense. And feeding the soil.

But with the use of bacteria instead of chelates, nutrients are available to plants much easier. There seems to be some use but that’s just my observation and have not done enough to compare. Maybe this summers.

I have never rinsed my plants unless the kelp meal sat on the leaves or chunks of any matter. But once dried it rubbs/falls off easily.
Most people defoliate, IMO a little later of good microbes is ok to block some light.

They help with heat stress also. As does aloe I believe and aloe also has enzymes that are beneficial as well as acting as a surfactant. As are sprout teas, plant teas.

Mammoth P is said to have microbes that can tolerate the swings of conditions we deal with. Because the compost microbiology cannot. So I just always add more to be sure.
It’s not salt. :). I haven’t leached,flushed or ph this last run. :).

Just did foliar application two day old cannabis seedlings under 200-250 ppfd. Tried on one day tomato seedlings in halide room but only 50ppfd. Tomatoes stayed darker green. Otherwise no difference. The LED on seedlings may be slightly bright at that height.

Not suggested till first true leaf I’ve heard. So far haven’t seen any issues.

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Foliar feeding - how often and for how long and for when in the grow cycle should one use foliar feeding re cannabis?

Also, how important is constant temperature and humidity in your grow rooms for holding down powdery mildew?

Thank you, Sam.

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Before flower. If need be couple weeks into flower. Really want to avoid the flowers/pistols IMO and I would try to have it ready to flower.
A root feed will be beneficial.

If you are foliar applying aerated compost tea then that is slightly different and can go little later. This will help prevent powdery mildew as well.

Maintain steady humidity. (Avoid massive swings but when u vent it will happen. Sealed rooms are easier to manage that. But still have to deal with smell.

Avoid Super high humidity (when lights go out there is a massive spike. Try pre cooling the room for an hour before lights out. (Or turn big lights off and use a second smaller one for last hour.
Less swing in heat and humidity. Try for slow movement in conditions.

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Foliar spraying plants both clones and plants in veg is very effective when done correctly. Some considerations with any foliar application are certainly 1. to pH the foliar solution 2. to keep an eye on humidity, heat and other factors - good room environment and control of that environment reduces the risk factors such as mold etc. 3. Spraying at the appropriate time in the light cycle to avoid light magnified by water droplets causing burn 4. using a good wetting agent or transport agent to insure product gets into the plant and light damage is avoided.

Our company HDI (best known for Clonex and Root Riot) specializes in a couple of foliar sprays that I have personally used and found work great. Clonex Mist is a product that was designed as a foliar spray " light mist application" for mom’s prior to cuttings and clones. It has a profile of seaweeds and aminos that help the cuttings root faster and maintain health and green vigor. We also have a very powerful Kelp called Nitrozime that has been around for many years used as a foliar during veg about once every 7 days to stimulate rapid growth and tight internode spacing. I definitely suggest anyone do their own research on these or other foliar applications. But I can stand behind these because I know them well and have used them.

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Something to keep in mind for commercial cannabis growers and spraying compost teas. I have seen farms fail thier microbial testing due to spraying compost teas to prevent PM. I’m not sure how often they sprayed and in what concentration, but I was told it was only sprayed in veg. Just food for thought. Having to blow hundreds of pounds of nice flower into oil isn’t always profitable.

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Foliar is important!!
Although plants have all the mechanisms to gather nutrients from their root mass, plants that put on mass and grow quickly and vigorously may still develop deficiencies even with proper fertilization.
Foliar helps the plant obtain nutrients at the site of photosynthesis (leaves) and can alleviate spot symptoms of deficiencies.
Another big advantage of foliar feeding is that you can help the plant maintain a better leaf surface pH. Leaf surface pH plays a big role in fungal vulnerability.

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I try to avoid foliar and I have great results. That’s not to say that foliar is not important, it’s just not part of my protocols.

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I like what you have to say here. We typically try to push cannabis to grow as fast as possible, so immobile nutrients can have a hard time keeping up - which can be assisted by micro nutrient foliar sprays. That’s speaking strictly about nutrients though. The benefits as far as pest and disease prevention are numerous!

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I also agree with you here. Foliar spraying is labor intensive and from my experience using it for nutrient deficiencies in a variety of applications, I’d say it’s a good tool when you’ve messed up your nutrition - but should be avoided in large by proper feeding at the root zone. I like it for cuttings though because they don’t have roots! Just talking about nutrition here, not IPM.

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I agree that Foliar is not the best method for feeding your plants but is very important when having a lockout issue or deficiency. The ability to feed from the stomata while flushing a lockout in the roots is a benefit. Also when having a deficiency it can be a more focused effort to fix in a hurry. We have a great New Foliar product called Foliar Science (29-9-9) High Nitrogen and will turn around a plant in a hurry.

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Like your foliar feeding thoughts re PH Mike C. How do you manage your PH?

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for foliar sprays to raise the pH one can use potassium bicarbonate, to lower a little, mixwell or acetic acid works.

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Thx Mike – none have dissolved carbon (carbonic acid) which is what cannabis plants thrive on in soluble form if applied to their leaves.

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IIRC, carbonic acid typically means dissolved CO2 in the water. its not really necessary imo if the grow space already has elevated levels of CO2 through gas injection.

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