When growing cannabis from cannabis seeds or cuttings it’s not uncommon to suspect nutrient burn if leaves show hints of yellow or brown near the tip. However, magnesium deficiency can mimic some of these signs, leading many growers to the wrong conclusion.
Getting the diagnosis wrong can seriously harm your plants. Adding extra nutrients to a magnesium-deficient crop may only increase plant stress. Flushing a plant that’s already low on magnesium can stall development even further.
Here’s how to correctly distinguish magnesium deficiency from nutrient burn. And how to easily deal with it.
Magnesium plays a vital role as a secondary macronutrient, forming a core part of chlorophyll and driving photosynthesis in your cannabis plants.
A shortage, or ‘Magnesium deficiency’ means leaves lose their vibrant green colour quickly.
Since Magnesium is a mobile plant mineral, the plant takes it from older foliage to fuel fresh growth. This is why older/lower cannabis leaves tend to drop off first with Magnesium deficiency. The classic ‘lower leaf shedding’ is seen whether growing from feminised seeds or autoflower seeds.
Common signs of magnesium deficiency include:
• Yellowing of the leaf areas between the veins (known as interveinal chlorosis).
• Green veins standing out against pale or yellow surrounding tissue.
• Issues appearing first on the lower, older leaves.
• Rusty brown spots developing as it worsens.
• Slight upward curling of affected leaves.
• A slow, progressive onset rather than sudden change.
One key difference between Magnesium deficiency and nutrient burn can often be seen in the leaves.
With Magnesium deficiency, older leaves commonly develop interveinal chlorosis — the tissue between the veins turns light green or yellow while the veins remain darker green. Leaf edges may also become dry or crispy over time.
Nutrient burn, by contrast, usually causes burnt-looking brown tips and margins without the characteristic interveinal chlorosis. In cases of excess nutrients — especially nitrogen — leaves are often very dark green and may appear glossy or clawed.
Nutrient burn occurs when your plants are fed with overly concentrated fertilisers, causing mineral salts to build up in the root zone and scorch leaf tissue from the edges inward.
The main indicators of nutrient burn include:
• Brown, crispy tips appearing first on the leaves.
• A scorched or burnt look at the leaf edges.
• Leaves sometimes turning unusually dark green (often indicating high N levels).
• Downward curling or ‘clawing’ of leaf edges.
• Visible salt crusting on the growing medium surface.
• Symptoms showing up rapidly, often right after a strong feed.
Magnesium deficiency in cannabis generally:
• Begins on the lower, older leaves.
• Features yellowing between the veins while veins stay green.
• Builds up slowly over time.
• Leads to an overall paler appearance across affected areas.
Nutrient burn generally:
• Targets the leaf tips and edges first.
• Produces brown, crispy, scorched tips.
• Hits fast following heavy nutrient applications.
• Can cause darker green leaves in certain situations.
Both nutrient issues create yellowing, brown patches, leaf curling, and stressed plants overall. The real giveaway is the location and pattern: magnesium deficiency issues show up as yellowing in the inner leaf areas between veins. Whereas nutrient burn starts at the outer tips and margins.
It’s also worth adding that a plant experiencing Magnesium deficiency may also be suffering from a lack of other mineral or nutrients. This can often complicate the picture, especially for the less experienced grower.
Finding a reliable feeding regime for their particular grow style can often be one of the more frustrating parts of the learning curve for the new grower.
As with all cannabis growth problems prevention is always better than cure. Soil growers should start with good quality soil, possibly with added slow-release organic nutrients for a mostly ‘water only’ grow method.
Less experienced growers may prefer to initially avoid attempting to re-use grow media. This is because recycled grow media (soil/coco etc) can require extra care and attention, it’s better suited to the slightly more experienced grower.
