Long Days and Bolting Spinach

I was out in the garden today and realized that the spinach is gone – it’s bolted. No it hasn’t run away or left the garden; it’s just started to send up flower stalks. I didn’t get to harvest very much spinach this year so I went on an internet search to learn some more about growing spinach and preventing bolting.

Bolting Spinach

Bolting Spinach

Bolting occurs when a plant transitions from its vegetative stage to its reproductive stage. Instead of growing leaves, the plant starts to grow flowers. This wouldn’t be that big of an issue if it weren’t for the fact that the chemistry of the leaves changes when bolting occurs. A plant’s leaves develop a bitter taste when it bolts. While we might not like this change in taste, it’s a great evolutionary trick that the plant has learned. By developing a bitter taste, it’s less likely that anything will eat the plant while it’s flowering and setting seed. This helps to make sure that the next generation of seeds is produced.

I’ve always known that spinach is a little tricky to grow in the spring. The plants seem to bolt so easily. There are some varieties that are more bolt-resistant than others but to me, none of the varieties I’ve grown have held up for very long in the spring. I’d always assumed that warm weather caused bolting in spinach and we almost always have warm days in May.

Come to find out, I was wrong! While warm day can speed the process, the length of day is the real determining factor of when spinach bolts. When there’s more than 14 hours of daylight, the spinach plants senses that it’s time to start reproducing. I checked on the local weather site and right now we’re having 15 hour days – no wonder the spinach is bolting even though it hasn’t been a warm spring.

If I want to grow spinach in the spring, I need to keep 14 hour days in mind. Here that happens in mid-May. To have a spring harvest I have to make sure that the spinach is sowed as soon as the ground can worked to give it as much time to grow as possible before that magic number of hours of daylight is reached. Also it means that once the middle of May has come, I should just harvest all the spinach that’s growing. Leaving it in the garden in the hope that the plants will get bigger will just give them a chance to bolt and turn bitter.

The other thing I could do is change my thinking about spinach entirely. Instead of thinking of it as a spring crop, I could see spinach as a fall crop. If the seed is planted in mid-August, the days are shorter and temperatures are on their way down. Since the ideal growing temperature for this vegetable is below 75°F and it can tolerate frost, growing it in the fall makes sense.

I’ve grown spinach in the fall in the past. While the seeds didn’t germinate well in warm soil, the ones that did germinate grew into large plants with dark green leaves – better than any spring spinach I’d ever grown. And in the fall the plants don’t bolt.

Years ago I stopped growing carrots in the spring and made them a fall crop. I’d found that the taste of a fall carrot was so much better than ones harvested in early summer. I also prefer fall beets because of their taste. Maybe I need to add spinach to this list as well. I may have to sow the seeds closer together to get a good stand but a few extra seeds is worth it to have a crop where I don’t have to worry about bolting. Plus when the onions are pulled, the peas are done and the first sowing of beans have stopped producing, there’s plenty of space in the garden for a few rows of spinach. Look for a post in October describing how a crop of fall spinach grew – it’s got to be better than this spring crop!


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