One of the key things that we need to understand as gardener's especially if we are trying to grow year round is the lifecycle of annual and biannual plants.
Different families and even varieties of plants all go to seed at fairly predictable times of year.
However just to make life interesting they also go to seed in response to stress
Let's take a look at some examples:
For example if we want to east carrots in spring, how do we achieve that when carrots naturally go to seed in spring? If we sow them in July for example and leave them in the ground ready to harvest in spring, they will have gone to seed before we an eat them. In the case of carrots 'going to seed' means throwing up a thick central flower stem (and eventually a beautiful flower) and if you try to eat the carrot you will find an extremely tough core, that makes it inedible.
The carrot lifecycle
So you have two options, you can sow you carrots in February/March and wait until July/August for them, or you can trick the carrot into thinking it was sown in February, by actually sowing it in November. Since November and February seem very simillar to carrots (cold, low light levels etc) you sometimes get away with it. Generally speaking I get to eat about 80% of my November carrots, the rest go to seed. Even February sown carrots sometimes go to seed, especially if the weather patterns confuse them or stress them.
So the best time to sow carrots is mid spring, provided you can protect them from carrot fly. For more on carrots, go to the section growing carrots all year round.
Another great example is spinach, which naturally goes to seed in spring. If you sow it in July for example it will give you perhaps one of two harvests and then run straight to seed. In the case of spinach 'going to seed' means that the plant starts to rise up off the ground, small rosettes of leaves start to from and then a central flower. The plant is still edible, but the leaves get ever smaller and thinner and increasingly bitter. You can still use them in a smoothie, with a banana to offset the bitter taste, but don't eat them on their own. Lettuce also goes bitter in the same way.
Spinach going to seed, not good eating
The best time to sow spinach is early-mid August for growing outside, or early September for planting under cover in October. Grown under cover I usually get over 20 harvests off my spinach before it goes to seed. For more on spinach, go to the section growing spinach all year round
One final example is the amazing brassica family, which also normally goes to seed in spring. If you sow in spring/summer you will find that in April all of your kale, cabbages, Brussels and Kalettes are a mass of flowers. In the case of most brassicas with a stem; every leaf junction, Brussel or Kalette throws out a flower stalk with a cluster of leaves. Every part of the plant is still edible and doesn't suffer from the bitterness of spinach and lettuce.
Kale going to seed, still great eating though
Of course sometimes going to seed is the whole point of the plant, so Broccoli, Calabrese and Cauliflower are all flowers. You might be surprised though to see your lovely cabbage heart split open to reveal a flower stalk in spring. With careful timings and selection of varieties though it's perfectly possible to eat brassicas all year round, the so called 'hungry gap' is the most challenging period, so I have a chapter specifically on growing for that period (April to June).
Although it might seem that plants are going to seed at a particular time of year, this isn't always the case. There are a few things that trigger this major life even. The most likely trigger is day length, for example 'Japanese' onions will start to bulb when day length exceeds 14 hours, UK main-crop onions when day length exceeds 16 hours.