Cannabis Cotyledons: What Seed Leaves Tell You About a Seedling
Quick answer: Cannabis cotyledons are the two round seed leaves that open first when a seedling breaks the soil. UC Agriculture and Natural Resources says they are part of the seed embryo, not true leaves, and hold the reserves the seedling lives on until its true leaves appear. Once the true leaves take over, the cotyledons wither, which is normal.
What Are Cannabis Cotyledons?
The word cotyledon means seed leaf. UC Master Gardeners say cotyledons are also called seed leaves, embryonic leaves and first leaves. They are not considered true leaves of the plant because they are actually part of the seed or embryo.
SDSU Extension explains what they do. A cotyledon is the part of a seed that contains food for the baby plant until it can make food with its own leaves. A UC ANR seed science lesson adds that the cotyledon usually stores food for the embryo plant and is often the first part of a seedling able to photosynthesize.
Why Cannabis Has Two Cotyledons
Botanists split seed plants into two broad groups. SDSU says plants with one cotyledon, like corn, are monocots, and plants with two cotyledons, like beans, are dicots. Cannabis is a dicot, so a normal seedling opens a matched pair of smooth, rounded leaves at the top of its first stem.
What Healthy Cannabis Cotyledons Look Like
The SDSU glossary describes cotyledons as the leaves of a plant embryo, which enlarge and store nutrients to feed the young plant after the seed sprouts. On a healthy cannabis seedling, that means:
- Two matching leaves. A pair of smooth, oval leaves, opposite each other at the top of the stem.
- Even green color. Firm and evenly green in the first days after they open.
- Smooth edges. No teeth or points, unlike the serrated true leaves that follow.
- Open and flat. The leaves spread out toward the light within a few days.
Treat these signs as a general guide, not a test. Seedlings vary, so judge them by how the true leaves grow in.
What Comes After the Cotyledons?
SDSU says that when a seed sprouts, the plumule becomes the shoot that produces the first true leaves, and the radicle becomes the first root. By the time the stored food is used up, the plumule has made true leaves, and the true leaves produce food for the plant by photosynthesis.
UMD Extension describes the same pattern for vegetable seedlings: the first true leaves appear above or between the cotyledon leaves. On cannabis, the first true leaves are narrow and serrated. Our guide to cannabis seedling true leaves covers what comes next.
How Long Do Cotyledons Last on Cannabis?
UC Master Gardeners say the cotyledon leaves wither and die when they are no longer necessary for the seedling’s survival. That timing varies quite a bit from plant to plant. The timeline below is a typical pattern growers see, not sourced cannabis data.
| Typical stage | What you see | Cotyledons |
|---|---|---|
| Day 0 | Seedling breaks the soil | Folded, often still in the shell |
| Around days 1 to 3 | Seed leaves open | Bright green and firm |
| Around the first week | First serrated true leaves appear | Still doing most of the work |
| Around weeks 2 to 3 | Two or three sets of true leaves | Start to pale or fade |
| Around weeks 3 to 4 | Plant growing fast | Often yellow, dry or dropped |
Watch the true leaves more than the seed leaves. If the new growth is green and healthy, fading cotyledons are part of normal growth.
Caring for Cannabis Cotyledons
- Give strong light from day one. UMD says seedlings need strong light from grow lights after they sprout, because window light is seldom enough. Our cannabis seedling light schedule covers hours and height for cannabis.
- Keep the mix moist, not wet. UMD says to wait until the top of the growing medium is nearly dry before watering, and to keep it moist but not wet.
- Water gently. UMD suggests watering the surface or letting the mix wick up water from a shallow pan, which avoids knocking over a young stem.
- Hold back on feeding. UMD says most potting mixes contain enough fertilizer to grow a seedling for 5 to 6 weeks. For cannabis timing, see our guide on when to start feeding cannabis seedlings.
- Keep temperatures moderate. UMD suggests 55°F to 60°F at night and 65°F to 70°F in the day for vegetable seedlings after they sprout.
- Leave the cotyledons alone. UC Master Gardeners say they are necessary for seedling development, so do not pick them off while they are green.
- Watch the true leaves. The health of new growth tells you more than the color of fading seed leaves.
Troubleshooting
Both cotyledons turn yellow early, and the true leaves are pale too. Check light, watering and feeding together. UMD warns that young seedlings are easily damaged by too much fertilizer, especially under moisture stress.
Cotyledons yellow while the true leaves look healthy. This is usually the normal handover. UC Master Gardeners say cotyledons wither once the seedling no longer needs them.
Cotyledons are slow to open and still wear the seed shell. The shell often loosens as the seed leaves expand. Pulling it off can tear the cotyledons, so keep conditions steady and watch for a day or two.
Cotyledons curl or cup. Check light distance, temperature and watering against the UMD seedling guidance above.
One cotyledon is missing or damaged. The seedling still has one source of stored food. Keep conditions steady and watch for the first true leaves.
The seedling falls over at the soil line. UMD says damping off fungi can quickly kill seedlings if the growing media stays too wet. See our guide to damping off in cannabis seedlings.
The stem stretches tall and thin. UMD says stems stretch and lean toward the light when it is too weak. Move the light or the seedling so it gets stronger light.
Sources
- UC Agriculture and Natural Resources, UC Master Gardeners, A Tiny Garden Surprise: https://ucanr.edu/node/107164/printable/print
- UC Agriculture and Natural Resources, Seed Science lesson (PDF): https://ucanr.edu/sites/default/files/2014-04/187907.pdf
- SDSU Extension, Plant Parts Study Guide (PDF): https://extension.sdstate.edu/sites/default/files/2023-03/MC-02913.pdf
- University of Maryland Extension, Care of Vegetable Seedlings: https://extension.umd.edu/resource/care-vegetable-seedlings
FAQ
What do cannabis cotyledons mean?
Cotyledons are the seed leaves, the first pair of round leaves a cannabis seedling opens. UC Master Gardeners say they are part of the seed embryo rather than true leaves. SDSU Extension says they contain food for the young plant until its own leaves can make food by photosynthesis.
Is it normal for cannabis cotyledons to turn yellow and fall off?
Yes, once true leaves are growing. UC Master Gardeners say cotyledons wither and die when they are no longer needed for the seedling's survival. If the true leaves are green and healthy, a yellow seed leaf is normal. If the new leaves are pale too, check light, watering and feeding.
Should you remove dead cannabis cotyledons?
There is usually no need. A fully dry cotyledon will drop on its own, and pulling on it can damage the young stem. Never remove green cotyledons, because UC Master Gardeners say they are necessary for seedling development and hold reserves the seedling is still using.
How long do cotyledons last on a cannabis seedling?
It varies. UC Master Gardeners say cotyledons wither when they are no longer necessary, which happens after the true leaves take over making food. On many cannabis seedlings, the seed leaves start to fade after two or three sets of true leaves appear, but that timing is a typical pattern, not a fixed rule.
Can a cannabis seedling grow without its cotyledons?
It depends on timing. UC Master Gardeners say cotyledons are necessary for seedling development, and SDSU Extension says they feed the plant until true leaves can make food. A very young seedling that loses both may struggle. Once true leaves are growing, losing the seed leaves matters much less.
