Ten Reasons Why Day Length Is Important

Right now sunrise is at 5:28 am and sunset is at 8:51 pm here is Rochester, Minnesota. I am writing this at 4:30 am on Friday so it is still pretty dark outside. I like to rise early and Friday's are my day for a men's small group at our church. So the coffee is on and I am listening to some Hillsong tunes on YouTube.

Day Length Illustrated in this Picture, Taken at About 8:00PM in April. Photo Credit: Reed Petersen

Right now the day length is approximately 15 hours and 21 minutes. In about three weeks we will top out at nearly 16 hours during the spring/summer solstice. Other than if you are a morning person "like me" or like to work in the garden until bed time "like me" (feels like double dipping this time of year) why should you care...

Here are 10 reasons...

1. Onions - Onions for Rochester, MN should be long day onions or they will pass through the day length requirements for bulb enlargement before you could plant them here in the open field (green houses excepted). For example, a southern short day onion like Vidalia won't bulb up here, as we pass through the 10-12 hour day length requirement in February or March. If you plant it here in April it will never bulb. The long day onions require 14-16 hours of day light which we have in May and June at this latitude.
2. Garlic - The story with garlic is similar to onions. Garlic is planted in October in the fall. It will root and sprout in the deep fall and then goes dormant until the ground thaws. It is then on auto-pilot for the spring, it is one of the first plants out of the ground and grows aggressively until late June when bulb development takes place. Like magic the green garlic bulbs to 3 inches in about 6 weeks. This is all triggered by day length. We start harvesting in early July here.
3. Lettuce - Have you noticed that lettuce is on a mission in the spring to spoil that beautiful head you have so carefully grown. If you miss it by so much as a week, the lettuce head elongates into a bitter seed stalk. This is all triggered by day length. In fact some lettuces are so sensitive to light that bolting can be triggered by strong street lights or florescent lighting in a room where transplants are being grown. 14 hours or more can trigger bolting a few weeks later. If you know lettuces tricks, you can succession plant every few weeks for a season long harvest.
4. Spinach - Is similar to lettuce except spinach can be planted in the fall and over wintered for an early bird harvest in mid to late April, after which it will typically bolt. Again succession planting every few weeks will allow you to slide around the bolting tendency. Spinach planted in September will never reach the day length requirements for bolting and will stay in top condition until freeze-up causes harvesting to cease.
5. Arugula - Gets very spicy right before it bolts, which is also triggered by day length.
6. Corn - Maybe it isn't so much day length but heat units with corn that get the job done for ear production. When we hit those long days in June, Dad used to say you could hear the corn grow. I've noticed that late planted corn often gets taller than early planted corn of the same variety. This is due to the long days in June and July.
7. Tomatoes and Pepper - Don't seem to have a strong day length requirement.
8. Morel mushrooms will always make their appearance in the spring about the same time. I think this may be as much soil temperature as day length.
9. Chickens loose and regrow their feathers partially due to low light in the winter. This is called molting.
10. SAD - Seasonal Affective Disorder, can cause depression in some people and is affected by day length. Most of us feel better when we can get outside during the day light hours.