Yellow Seedling Leaves – Why Are My Seedlings Turning Yellow

By Liz Baessler

Have you started seedlings indoors that began healthy and green, but all of a sudden your seedling leaves turned yellow when you weren’t looking? It’s a common occurrence, and it may or may not be a problem. Keep reading to learn more about yellowing seedling plants and how to treat them.

Yellow Seedling Leaves

The first thing to establish is which of your seedling leaves turned yellow. When seedlings emerge from the soil, they put forth two starter leaves called cotyledons. After the plant becomes more established, it will begin producing differently shaped leaves that are characteristic of its species.

The cotyledons are designed to get the plant started in the very beginning of its life, and once it’s producing more leaves, these aren’t really needed anymore and will often yellow and eventually fall off. If these are your only yellow seedling leaves, your plants are perfectly healthy.

Why are My Seedlings Turning Yellow?


If it’s the larger, more mature leaves that are turning yellow, you do have a problem, and it could be caused by any number of things.

Are you giving your seedlings the right amount and intensity of light? You don’t need to buy a fancy grow light for healthy seedlings, but the bulb you do use should be trained about as close as possible directly over your plants and attached to a timer that keeps it on for at least 12 hours per day. Make sure you do give your plants a period of darkness, too, of at least 8 hours.

Just as too much or not enough light can cause yellowing seedling plants, too much or too little water or fertilizer could also be the problem. If the soil around your plants has been completely dried out between waterings, your seedlings are probably just thirsty. Overwatering, however, is a very common cause of sickly plants. Let the soil begin to dry a bit between waterings. If you’re watering every day, you may very well be doing too much.

If water and light don’t seem to be the problem, you should think about fertilizer. Seedlings don’t necessarily need fertilizer so early in their lives, so if you’ve been applying it regularly, that may be the problem. Minerals from fertilizer can build up very quickly in seedlings’ small containers, effectively strangling the plants. If you’ve applied a lot of fertilizer and can see white deposits around the drainage holes, flush the plant gradually with water and don’t apply any more fertilizer. If you haven’t applied any and your plant is yellowing, try a single application to see if it perks up.

If all else fails, plant your seedlings in your garden – new soil and steady sunlight might be just what they need.

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