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Potential Causes of Slow Plant Growth (101)

Vandenberg

Active member
420giveaway
Overwatering:
Soil moisture that is not absorbed rapidly turns stagnant; the plant quickly uses up any oxygen within the water, then is unable to respire further, resulting in moisture low in o2.
Pythium thrives in low-oxygen (anaerobic) conditions.
in short, overwatering will slowly suffocate your roots, preventing sufficient oxygen uptake by the roots, and ultimately causing root rot.

Light Deprivation
Although your plant may be receiving light, particular strains may require higher light levels than others.
A recommended light level for full bud development is 50 watts/m2. Edit: per square foot. :)
Full sunlight is 100,000 lumens max.

Low Nutrient Strength
The plant is unable to acquire the necessary amounts of nutrients to sustain high growth rates.
Large and mature plants can take higher nutrient strengths.
Nutrient strength is also related to the light intensity; plants under fluorescent lights usually require a lower nutrient concentration than under HIDs.

Nutrient Lock-up
Adding too much of a nutrient (ex. Magnesium) can "lockup" one or more nutrients, rendering them chemically unavailable to the plant.
Nutrient lockup can occur at extreme pH ranges (ie. under 5.0, over 7.0).

Light Spectrum
Light that does not contain enough red spectrum (too much blue).
Light spectrum can have a dramatic effect on plant growth, with different light frequencies affecting different photosynthetic processes within the leaf.
Selecting a blue spectrum in a vegetative growth phase is preferred, with red spectrum in flowering.

PH
pH is too high or too low (ie. acidic soil. The plants come out as mutants).
Plants are unable to absorb nutrients, or in adequate quantities within certain pH ranges.
Optimum pH varies with each medium.
Hydroponics and aeroponics: 5.6-5.8.
Soilless: 6.0-6.3
Soil: 6.5-7.0.
Some soilless mixtures can be fairly acidic, due to their high % bark content.

Low Temperatures
Plant metabolism will decrease at low temperatures. Chemical reactions within the plant will take longer.
Optimum plant growth often requires close temperature regulation; daytime temperatures between 25C and 30C are preferred.
Differences in the daytime and nighttime temps should not be dramatic, as this difference may shock the plant.

Low Soil Temperatures
Evaporation from a medium (i.e. peat pots) tends to chill the medium quite a bit due to the evaporative cooling effect.
As the peat pot warms, it draws moisture outward, the evap effect cools the peat (like sweating).
New growers often make the mistake of adding excessive amounts of water, resulting in cold soil, poor root formation and slowed growth
(Original Source "Snoofer")

Happy growing y'all
Vandenberg :)
 
Last edited:

Vandenberg

Active member
420giveaway
Killing them with kindness...

Killing them with kindness...

The number one sin of new growers has to be the killing off of their plants with the attempted kindness of watering too frequently (especially in plastic pots) which can lead to lack of oxygen in the root zone which leads to anaerobic bacteria thriving that will gobble up your roots.

A senior member here named Ichabod Crane posted in another thread here an idea that makes sense to me in certain applications:

Top dress with NAPA floor dry. It is silica stone or also known as DE. It turns tan when wet and white when dry. Then all you have to do is watch the color. When it turns white all across the top you can water. If it is tan it is still wet.
Clever.

Vandenberg :)
 
Last edited:

Creeperpark

Well-known member
Mentor
Veteran
Very helpful information. The only thing I question is the "Low Nutrient Strength" part. The conductivity of the nutrients are determined by the Cation exchange capacity and not the amount of, or the "Nutrient strength" available.
 

roybart

Member
Interesting read but 50w per m2 seems like a typo to me, should be around 50w per square foot.
What kind of watts LED HPS Flouro's the type of light will change the wattage

Seedlings, ClonesUnder 100 PPFD Veg, Greens 150 PPFD - 400 PPFD Extended Veg with healthy plants 350 PPFD to 500 PPFD Flowering, Fruits 400 PPFD to 800 PPFD Flowering with Supplement CO2600 PPFD to 1100 PPFD
https://www.waveformlighting.com/horticulture/convert-lux-to-ppfd-online-calculator this will put you in the ballpark.


Good job all round
 

H e d g e

Active member
‘What kind of watts LED HPS Flouro's the type of light will change the wattage

Fruits 400 PPFD to 800 PPFD‘


Hi roybart! My point was that it would not be possible to achieve 400 ppfd to 800 ppfd at 50w per m2 with any of the lighting options that you have mentioned. You would need something closer to 50w per square foot.
 

TexanTerps

Active member
can seedlings tolerate higher light like in a veg room? i feel i may be overlighting with a mars sp1000 equivalent at 2.5ft at 100 percent
 

Creeperpark

Well-known member
Mentor
Veteran
TexasTerps raise the mars sp1000 as high as you can from the seedlings. Let them get just a little lanky or leggy and then drop your light down. Those are very nice lights and will do a good job for you.
 

Billythekid

New member
Can anyone help?

Can anyone help?

Hello everyone. First post on here for me, but i ussually use this site as my go to for info. I seem to be having some trouble with my plants, they're showing some kind of deficiency on the leaves. I use a substrate that already has perlite mixed in it... i live in a country where weed is decriminalized but still not legal so it's hard get my hands on some nutients that are made specifically for canabis so i tend to just use stuff i find in my local plant shop and have had pretty decent results untill now. Can anyone tell me what this could be? Its seems to only be affecting the plants of a certain strain. Although today i say some very small dots of rust on another strain aswell but might not be related. Anyway, ill attach a few pics and hopefully someone can help me out!
 

Billythekid

New member
Pics

Pics

Here are some pics of them
 

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Dr Watt

Who What
The Age of a Mother Plant ? :skiiing:

Overwatering:
Soil moisture that is not absorbed rapidly turns stagnant; the plant quickly uses up any oxygen within the water, then is unable to respire further, resulting in moisture low in o2.
Pythium thrives in low-oxygen (anaerobic) conditions.
in short, overwatering will slowly suffocate your roots, preventing sufficient oxygen uptake by the roots, and ultimately causing root rot.

Light Deprivation
Although your plant may be receiving light, particular strains may require higher light levels than others.
A recommended light level for full bud development is 50 watts/m2. Edit: per square foot. :)
Full sunlight is 100,000 lumens max.

Low Nutrient Strength
The plant is unable to acquire the necessary amounts of nutrients to sustain high growth rates.
Large and mature plants can take higher nutrient strengths.
Nutrient strength is also related to the light intensity; plants under fluorescent lights usually require a lower nutrient concentration than under HIDs.

Nutrient Lock-up
Adding too much of a nutrient (ex. Magnesium) can "lockup" one or more nutrients, rendering them chemically unavailable to the plant.
Nutrient lockup can occur at extreme pH ranges (ie. under 5.0, over 7.0).

Light Spectrum
Light that does not contain enough red spectrum (too much blue).
Light spectrum can have a dramatic effect on plant growth, with different light frequencies affecting different photosynthetic processes within the leaf.
Selecting a blue spectrum in a vegetative growth phase is preferred, with red spectrum in flowering.

PH
pH is too high or too low (ie. acidic soil. The plants come out as mutants).
Plants are unable to absorb nutrients, or in adequate quantities within certain pH ranges.
Optimum pH varies with each medium.
Hydroponics and aeroponics: 5.6-5.8.
Soilless: 6.0-6.3
Soil: 6.5-7.0.
Some soilless mixtures can be fairly acidic, due to their high % bark content.

Low Temperatures
Plant metabolism will decrease at low temperatures. Chemical reactions within the plant will take longer.
Optimum plant growth often requires close temperature regulation; daytime temperatures between 25C and 30C are preferred.
Differences in the daytime and nighttime temps should not be dramatic, as this difference may shock the plant.

Low Soil Temperatures
Evaporation from a medium (i.e. peat pots) tends to chill the medium quite a bit due to the evaporative cooling effect.
As the peat pot warms, it draws moisture outward, the evap effect cools the peat (like sweating).
New growers often make the mistake of adding excessive amounts of water, resulting in cold soil, poor root formation and slowed growth
(Original Source "Snoofer")

Happy growing y'all
Vandenberg :)
 
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