What to do when St. John’s wort plant leaves turn yellow & fall off

The leaves of st. john’s wort plants (also known as Hypericum perforatum) can turn yellow and brown for reasons within or beyond your control. Here are the most common causes and steps you can take to make the foliage of the st. john’s wort plant look green and healthy again.

Underwatering or overwatering is bad for St. john’s wort plants

Improper watering is usually the main culprit when yellow or brown leaves start to develop on St. john’s wort plants. Flowering plants like St. john’s wort plants benefit from deep regular watering. This isn’t just for maintaining the health of leaves but to also maximize the potential of the bloom period. Underwatering St. john’s wort plants could result in yellow leaves as the plant wouldn’t be able to produce enough energy with a key component (water) missing from photosynthesis.

Overwatering can also damage leaves as excessive moisture can clog the soil and prevent the St. john’s wort plants from ‘breathing’. Soil drainage plays a key role in this respect.

As a general rule of thumb, we would recommend watering St. john’s wort plants once a week and increasing or decreasing the frequency of watering according to the weather (e.g. water more if the weather is hot, water less if the weather is cold).

Proper drainage of water from soil

You won’t be able to properly gauge the frequency of watering the st. john’s wort plant needs if it is being grown in soil that doesn’t drain well. Compacted soil can cause a number of issues for st. john’s wort plants such as preventing root growth, reducing nutrient absorption, and preventing oxygen absorption. All of this can cause leaves to turn yellow and fall off. you will know if the soil is waterlogged by creating a tiny hole on the soil surface and filling it with water. If the water hasn’t drained after a few hours then you are dealing with clogged soil problems.

To stop more leaves from turning yellow, you will most likely need to transplant the st. john’s wort plant into soil that drains well. One way of doing this is by mixing the soil with material like perlite, compost, and shredded leaves.

Excessive sunlight or lack of sunlight

Yellow leaves can also form on st. john’s wort plants due to changes in sunlight conditions. Prolonged exposure to direct sunlight, for example, can harm plants because it can result in sunburn and the scorching of leaves. Lack of sunlight could have the same negative effect on st. john’s wort plants as it would result in the leaves not getting enough light to drive photosynthesis. Lack of energy would then cause the leaves to wilt and gradually become discolored.

Try to position the st. john’s wort plant or provide it enough cover or exposure so that it receives an optimal amount of sunlight, which is about per day.