A reader emailed me earlier this week with the following question:
I started some broccoli seed last month and they have been growing really well, but now some of the seed leaves are turning yellow and falling off. Is this normal? What should I do?
The answer is yes, this is completely normal!
The seed leaves (cotyledons) is where a seed’s energy is concentrated. These initial leaves are what supplies the forming seedling with the energy it needs to form roots, extend a stem, and ultimately start to grow into a little plant. By the time the energy in the cotyledons runs out, the seedling has developed roots and true leaves, and is starting to draw its own nutrients from the soil and photosynthesize energy from the sun. Having served their purpose of transitioning the seed to a self-sustaining plant, they will eventually fully expend themselves and fall off (typically after 2-3 true leaves have emerged).
The timing may vary, depending on the type of plant and the variety, and the process may happen gradually, where you can see the cotyledons slowly yellow, wither, and dry up, or it might happen a little more abruptly where the plant simply lets go and the cotyledons drop, but is a natural part of the plant’s life cycle and generally speaking, you don’t really need to do anything to help the process along. However, if the seed leaves are still attached when you are ready to transplant it into the garden, go ahead and snip them off with a scissors (assuming, of course, that there are at least a couple sets of true leaves), as by that point they are very close to the ground and can be an entry point for pests and disease.
Now, if your seed leaves are discolored or dropping and you do not see any true leaves yet, that would be reason for concern. In this case, you’ll want to check out the growing conditions in your seed flats to figure out what is going on. Damping Off, over/under watering, or cold soil/air temperature would be likely culprits.
Do you have a gardening question you’d like to see answered on the blog? If so, please contact me!
And speaking of ways to contact me, I have set up a Tubmlr feed for the blog, so Tumblr users can now follow, share, and comment directly from their Tumblr dashboard (social media icon to follow).