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How Does Day Length Affect Plants?


Question: How Does Day Length Affect Plants?

Certain plants' sensitivity to day length, photoperiodism, determines when the fruit or bolt. This explains why some cool-season crops grow better in spring than in fall, or vice-versa: even though the temperatures may be similar, the length of daylight is quite different. Learn more about how to use this knowledge to increase the productivity of your garden below.


The way plants attune themselves to the amount of daylight they get is known as photoperiodism. This affects every facet of the plant's growth, from when it will bloom, when it will set fruit, or even when it's time to bolt.

There are three basic types of plants when it comes to how day length affects them:

  • Long-day plants
  • Short-day plants
  • Day-Neutral plants

Long-day plants are those that start blooming once the days start getting longer; increased daylight spurs them to start blooming, which leads to fruiting.

Short-day plants are those in which a lesser amount of sun inhibits flowering. These plants do best in early spring or in autumn, when there's less daylight than in, say, midsummer.

Day-neutral plants are not affected by the amount of daylight at all. For these plants, factors such as their stage of maturity or the temperature dictate when they will bloom.

So, what does this mean for your garden?

First of all, it means that if you have had zero luck fall-planted beets, even though all the books tell you they can be planted reliably in both spring and fall, it's not your fault. You can blame day-length, since beets are long-day plants. This has been the case in my own garden: spring-planted beets flourish here, and fall-planted ones are good for little more than harvesting a few beet greens.

Some long-day vegetables include beets, carrots, fennel, lettuce, peas, radishes, spinach, and turnips. These are best planted when the days start lengthening. Short-day veggies include beans, cucumbers, okra, some tomato varieties, and potatoes.

Many common vegetables don't care either way how long the days are, as long as the temperatures are right and they're getting the care they need. These easy-going plants include Brussels sprouts, cabbage, corn, kale, kohlrabi, parsnips, and rhubarb. These can be planted at any time, as long as you keep your first and last frost date in mind.

Now that you understand why some spring-planted crops just don't do as well in your garden, you can start planning accordingly. Personally, I've decided that fall-planted beets in my garden are just more trouble than they're worth.

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