Why Is My Plant Turning Yellow?

There are two likely explanations for why your plant is turning yellow. The most important question is: which leaves are turning yellow?

Are they the leaves at the top of the plant? Or the leaves at the bottom?

Let's explore both possibilities!

Why are the leaves at the top of my plant turning yellow?

If the new growth (top leaves) are turning yellow before the rest of the plant, it's likely that the pH of your substrate is too high and you're causing the plant to lock out micronutrients.

Yellow leaves at the top indicate micronutrient lock out

Different nutrients become available to the plant at different levels of pH so it's important to keep your substrate and your water within the optimal range so that your plant has access to a full spectrum of nutrients.

For cannabis plants growing in soil, that range is between 6.0 and 7.0. Cannabis plants growing in hydroponic systems should be kept between 5.8 and 6.5.

You can easily correct pH issues by measuring the pH of your substrate with a soil pH tester and then adjust the pH of your water to offset the imbalance.

You'll need a good pH meter and a pH adjustment kit to restore the pH balance and keep it from getting too high in the future.

Color should return to the top of your plants within a few days.

Why are the leaves at the bottom of my plant turning yellow?

If the leaves at the bottoms of your plant are turning yellow but the leaves at the top remain green, your plant is likely suffering from a nitrogen deficiency.

These plants are both suffering from a nitrogen deficiency

Nitrogen deficiencies are the most common ailment in cannabis plants. Luckily, they're also one of the easiest deficiencies to correct.

Nitrogen-based fertilizers are easy to obtain and simple to use.

Be sure to verify that the pH of your substrate is within the acceptable range outlined above to avoid misdiagnosing the problem.

You should see the green color return to the lower leaves in about 4-5 days after the first application.