Don't Transplant Seedlings Until You See True Leaves or Your Plants Will Struggle – Here's What to Look For

If you ever grow a plant from seed, you will discover firsthand that true leaves are not the first ones to emerge from the seed. The true leaves on seedlings come later and are the life force of the plant.

Many people are surprised to find that the first leaves out of a seedling don’t stick around. This initial set of cotyledons doesn’t last long and is quickly replaced by the first set of true leaves. Understanding this process and being able to identify cotyledons versus true leaves is an important lesson to learn for beginner gardeners.

Let’s take a look at how leaves emerge from seeds and when the first true leaves emerge. Learning to spot this key stage in the seed starting process will help you discern the perfect time to transplant and how to care for your seedlings at the beginning of their lives.

Seed Starting 101

When contemplating growing plants from seed, first research the plants to find out whether they need stratification or scarification or whether seed starting is the best option for the type of plant you want to grow. Not all plants come true from seed and others can take months to germinate.

When you are ready to start your seed adventure, gather your materials and get ready to grow. To coax a seed from dormancy it needs warmth, water, oxygen, and light. When starting seeds indoors, use a high-quality seed starting mix like this one from Miracle-Gro to fill a cell tray or small pots. Add two or three seeds per cell, cover with soil if needed, and water. Cover with a vented plastic dome or plastic bag to help hold in moisture.

If you have a heating mat like this one from Amazon to set the tray or pots on, the seeds will germinate faster. Setting it on top of the refrigerator can work in a pinch, too, as an easy heat source. After the seeds germinate, they will need more light, either from a south-facing window or grow lights, like this affordable LED light from Amazon. You also can direct-sow the seeds outdoors if the last frost is past.

A seed contains an embryo with everything it needs to start a new plant. So when all the ingredients come together to break dormancy, the seed coat softens and metabolic processes begin. Seeds used this stored energy to first push out tiny roots downward, followed by stems and leaves that grow upward toward the light.

The First Leaves You See

The first leaves you see after sprouting a seed are called cotyledons or seed leaves. These are not true leaves and they will eventually turn yellow and fall off after enough true leaves emerge. Cotyledons continue to provide nourishment until the true leaves take over.

Cotyledons look different from the plant’s actual leaves and supply nourishment to the plant until it can make its own food through photosynthesis. Their shapes vary with the type of plant. They can be round or oval, heart-shaped, or elongated and usually bear no resemblance to the plant’s true leaves.

If only one narrow leaf emerges, the plant is a monocot and its embryo contains only one cotyledon. Examples include bananas, ginger, orchids, corn, rice, and wheat. If two leaves emerge, it is a dicot and its embryo possesses two cotyledons. Examples include almonds, cashews, peas, apples, and plums.

What Are True Leaves?

True leaves on seedlings emerge after the cotyledons, which can take weeks. You will recognize the true leaves because they look like the leaves on the mature plants you are growing. They get their energy from the sun through photosynthesis, which enables the plant to grow and develop.

Now that the cotyledon’s job is done, it drops off and your seedling matures and grows only true leaves. The development of the first set of true leaves is a vital step in the seed starting process. It signals when your plant is big enough to transplant outdoors or move to a bigger pot.

When to Transplant Seedlings

You can transplant the seedlings anytime after the first set of true leaves appear, but it’s better to wait for a couple sets of true leaves. By this time, your seedlings’ stems should be getting thicker and stronger and the true leaves should be growing bigger to take in more sunlight and help fuel your plant.

Transplanting seedlings with only the cotyledons is risky. The cotyledon roots and stems are very fragile and not easy to move. If you must transplant seedlings early before the first true leaves appear, be sure to provide ample soil around the roots.

When moving seedlings outdoors, you must harden off plants first to prevent sunburn, wilting, or shock and to prepare them for the harsh outdoor conditions. You can move seedlings in and out each day, gradually increasing their time outside over a two-week period. Or you can start them in a shady area outside and gradually move them to more and more light each day.

Seed Starting Essentials