The small, oval leaf below the true leaves is the tomato cotyledon.

The small, oval leaf below the true leaves is the tomato cotyledon.

If you start seeds indoors, you’ve probably read the phrase, “when the seedling has a set of true leaves….” or something to that effect. What are true leaves?

When a seed germinates, it bursts out of its seed coat and sends up a stem. Some of these stems have one leaf (called a monocot) others have two leaves on it (called a dicot). Tomatoes, for example, are dicots, while corn is a monocot. Cotyledons are part of the seed and, on many plants, they provide photosynthesis as the plant grows. A bit later, a plant will form its first “true leaves.” These leaves have the appearance and function that all future leaves will have, and they may look dramatically different than the cotyledons.

For seed starters, it’s important to remember not to transplant seedlings until they have some true leaves. Here’s a short video from the University of Illinois Extension Service on the difference between ctyledons and true leaves.

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  1. […] else the plants need to sprout. So avoid fertilizing the seedlings for around 1-2 weeks until the first pair of true leaves appear. At this moment, you need to transplant your cilantro into a larger pot with a good quality potting […]

  2. […] Minnesota State Horticultural Society emphasizes never to transplant your seedlings until they have developed true leaves. This is the […]

  3. […] What are true leaves and how do you know that your basil seedlings have grown one? After a few days after planting your basil seed, seed leaves will sprout from the cotyledons of the seedlings. Once the root establishes itself in the soil, only then will the second set of leaves or the “true leaves” emerge. […]

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