Cannabis likes a comfortable room temperature (they like about the same temperatures as we do).
When there is a phosphorus deficiency, the lower (oldest) leaves turn dark green. Leaves occasionally get a bluish or bronze tinge, and may thicken or curl downward before exhibiting dark gray, bronze or purplish splotches. Sometimes the stems of the affected leaves will turn bright red or purplish, usually starting from underneath.
If you cannot get rid of your phosphorus deficiency, please consult our 7-Step Cure to 99% of Cannabis Growing Problems
- tends to affect the lower and older leaves of the plant
- sometimes a phosphorus deficiency is accompanied by bright red stems (though not always), though if you have red stems but no other symptoms, it’s typically not something to worry about
- leaves darken (turning a dark green, blue or grayish color) and may appear shiny
- leaves may start turning yellow in places if the phosphorus deficiency is left untreated, or if the deficiency is combined with other nutrients deficiencies and/or pH problems. However, yellow leaves is typically not associated with the beginning of a phosphorus deficiency.
- leaves get bronze, purple or brown spots and splotches
- leaves thicken and may feel dry or stiff
- stems sometimes turn bright red or purple, but not always
- sometimes accompanied by a Calcium deficiency, as Phosphorus and Calcium interact with each other inside the plant
- this deficiency is more common after buds start forming, when the plant is using a lot of Phosphorus
Phosphorus deficiencies in the vegetative stage usually appear at the bottom of the plant on some of the oldest leaves, and will progressively climb up the plant if left unchecked.
Cooler temperatures lower than 60°F (15°C), as well as large temperature swings, can make it harder for the plant to absorb phosphorus. Cannabis plants are therefore more likely to show signs of a phosphorus deficiency when the temperature drops too low, or if they go through a cold spell.
After going through all the above steps, watch to make sure that the phosphorus deficiency starts to clear up within a few days to a week or so. After a phosphorus deficiency is cleared up, the problem (brown spots, unhealthy lower leaves, red/purple stems, etc) will stop appearing on new leaves, usually within a week.
Just remember that if there’s no actual phosphorus deficiency currently appearing on your cannabis plant, adding more phosphorus is probbaly not going to help plants grow better or make bigger buds – in fact adding too much phosphorus may actually hurt your plants by preventing the uptake of other nutrients! While it’s difficult to overdose your plants on phosphorus, adding too much compared to other nutrients will often cause other strange & unexpected deficiencies to appear.
Sometimes you will get a cannabis phosphorus deficiency, and the stems do not appear red or purple at all, or the coloring may not be pronounced.
Phosphorus deficiencies cause dark splotches on leaves and can appear at the bottom of the plant on some of the oldest leaves. Learn to spot & fix the issue.
Red stems can be caused by nutrient deficiencies caused by too-high or too-low pH. This leaf is suffering from multiple problems including red stems.
Some plants (especially strains that produce purple buds or leaves) will naturally grow colorful stems. These stems may be reddish but typically look closer to purple than bright red. The purple color appears on stems all over the plant as opposed to just places that are getting light. There’s nothing to worry about in this situation, so you can just enjoy the purple 🙂
In this case, you probably have nothing to worry about as long as you aren’t seeing any other symptoms and plants are growing fast and healthy.
Since too much light can cause red stems and other symptoms of stress, it’s always a good idea to keep your grow lights at the distance recommended by the grow light manufacturer. LED grow lights especially are infamous for light-burning plants if kept too close (it’s common for growers to keep moving them closer since they run cool).
If the temperature of your growing environment seems extreme to you, it may be stressing out your plants. Each strain is different, but cannabis plants generally grow best in temperatures that are considered comfortable or slightly warm to humans. You should be able to put a hand where your plants are under the light and hold it there comfortably for 30 seconds. If it feels too hot for your skin, it’s likely too much heat for your plants. Learn how to create a perfect plant environment.
How exactly does pH affect nutrient absorption?
These are strong liquid supplements that can be added directly to the water to adjust the pH. Use a small amount of liquid to start, just a 1/8 tsp or a few mL (PH Down is especially concentrated). There is also Natural PH Down and Natural PH Up which are suitable for use in organic setups.
If you’ve been giving your plants good nutrients and ruled out all the above factors, your red stems are likely caused by a…
How to adjust pH?
What causes red stems in cannabis plants? You’re checking on your plants, things have been going pretty well. Then one day you notice a plant has bright red stems. Maybe there are other symptoms,