Should I cut off yellow leaves?

Yes, you can snip them off with clean scissors. This keeps the plant looking tidy and helps you spot new issues.

Does yellowing mean it needs fertilizer?

Usually not. Yellowing is most often a water issue, so fix the moisture levels before adding any plant food.

Square-stalked St. John's-wort: yellow leaves

Check these first

Touch the top inch of soil to see if it is dry.
Check the bottom of the pot for standing water.
Inspect the undersides of leaves for orange rust spots.

Likely causes

Inconsistent moisture
Most likely
How to tell: The leaves turn yellow and feel brittle or dry to the touch. This happens when the soil dries out completely between waterings.
What to do: Keep the soil consistently damp by watering every 2 to 4 days. Check the top inch of soil daily and add water before it feels dry.
Waterlogging
Possible
How to tell: The leaves turn a soft, pale yellow and the stems may look limp. This occurs if the pot has poor drainage or sits in standing water.
What to do: Ensure your pot has drainage holes at the bottom. Empty the saucer 30 minutes after watering so the roots do not sit in water.

Yellow leaves on other plants

Find out what's wrong with your square-stalked st. john's-wort

The list above covers the usual causes. Pocket Botanist looks at a photo of your actual plant and tells you the likely cause, how serious it is, and what to try first. Identification and a health check are free.

When to worry

Worry if the yellowing spreads rapidly across the whole plant. It is normal for the oldest, lowest leaves to yellow and fall off as the plant grows.

Stopping it coming back

Maintain a steady watering rhythm and use a well draining potting mix to keep the roots happy.