Magnesium deficiency vs nutrient burn in cannabis

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.

What is magnesium deficiency in cannabis?

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:

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.

What is nutrient burn in cannabis?

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:

Magnesium deficiency vs nutrient burn: key differences

Magnesium deficiency in cannabis generally:

Nutrient burn generally:

Why magnesium deficiency is often confused with nutrient burn

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.

How to confirm magnesium deficiency

Avoid the temptation to make a hasty and potentially incorrect diagnosis. Before acting, double-check these factors:

How to fix magnesium deficiency

Quick recovery steps include:

Perhaps most importantly, make mental notes for next time. Know the early signs of deficiency, implement learnings into your feed schedule. Improve your grow medium preparation. Consider Cal/Mag supplements as part of your future nutrient regime

How to fix nutrient burn

Over feeding, along with over watering, are two of the most common errors to affect less experienced growers. Cannabis roots will grow prolifically in the right conditions. But they are easily damaged if waterlogged or if given minerals/nutrients that are simply too concentrated. Nutrient burn damages roots, stunting growth and leaves visible brown leaf damage.

If nutrient burn is seen, don’t delay. Act quickly to prevent further damage:

Can both happen at the same time?

Unfortunately, yes. Excessive feeding leads to salt accumulation that blocks Magnesium uptake, blending the two problems. Carefully assess your nutrient levels, pH, drainage and grow-room conditions to pinpoint the root cause. Flush the plants.

Many coco growers find it best to deliberately produce run-off to try to control mineral build up. Other growers err on the side of under-feeding rather than over-feeding in an attempt to avoid nutrient burn.

Ultimately both Magnesium deficiency and nutrient burn are both relatively ‘common’ feed-related issues. Finding that easy-to-use recipe that keep your plants in the nutrient sweet spot from cannabis seed to harvest is the best way to free yourself from worry.

Prevention tips

To prevent magnesium deficiency:

Avoid nutrient burn by:

Frequently asked questions