If the leaves on your spinach plant were once full, fleshy and oval, but are now thin, narrow, and resemble pointed arrows, it means your spinach plant is in the process of bolting. The spinach plant is preparing to flower and produce seeds.
The structure of new spinach leaves change when the plant is begins redirecting its nutrients and resources to the production of a flowering stem (aka “going to seed”). Not only are your spinach leaves smaller and pointy, they are also bitter. This is because of the plant’s production of sesquiterpene lactone compounds. Some plants produce these compounds in response to stressors, but this also just occurs naturally when the plant’s internal clock triggers reproduction. When spinach begins its flowering stage, the levels of sesquiterpene lactones increase as a means of defending the plant during its final, reproductive stage.
What Triggers Bolting:
Bolting can just be the end result of the spinach plant’s life cycle, or it can be the plant’s defense response to a stressor.
- Environmental factors such as heat, draught, soil condition, and sun exposure.
- Bacteria and fungus infections.
- Leaf eating pests and herbivores.
- Transitioning from vegetative production to flowering.
What Can You Do To Stop Bolting?
Unfortunately for this particular plant, there isn’t anything you can do other than harvest any remaining salvageable leaves if they are still edible and let the plant finish flowering if you are going to collect its seeds.
You can try pinching off the flowering stem, but the plant will just continue to try sending up new flowering stems with the resources it has remaining, and the leaves will likely remain bitter.
You can prevent bolting in future crops if it was the result of a stressor and you correct or address the cause with your next crop.
For healthy plants, bolting is just a part of its natural life cycle. A few studies have suggested that the reproduction trigger is a result of the cumulative length of time to sun exposure. Plants exposed to shorter periods of daylight (8 hours versus 14 hours) tended to bolt later even in higher temperatures. One approach might be to start your spinach seeds indoors and provide only 8 hours of sunlight per day until the plants are transplanted outdoors.