'Are you going to tell me,' said Arthur, 'that I shouldn't have green salad?'
'Well,' said the animal, 'I know many vegetables that are very clear on that point. Which is why it was eventually decided to cut through the whole tangled problem and breed an animal that actually wanted to be eaten and was capable of saying so clearly and distinctly. And here I am.'

-Douglas Adams, The Restaurant at the End of the Universe

• Onion: Onions should be picked when the stem falls over


• Radish: You should be able to see the top part of the radish root pushing itself up out of the ground a little bit. If it looks about the size you expect that specific radish variety to mature to, they should be ready to harvest when they reach that size. Sometimes you have to scrape dirt. If your radish is all leaf and no radish, then that's usually a planting/thinning issue; you need to thin them to the proper spacing while they are very small.


• Potatoes: New potatoes should be ready for harvest after 10 weeks. Harvest all the potatoes once the vines die so they don't rot in the ground.


• Tomatoes: Usually when the turn red, but some of the heirloom varieties are different colors (yellow, purple)


• Peppers- the problem with peppers is that some you want green, some yellow and some red, and unless you know what you planted, you aren't sure when to pick.


• Broccoli: Monitor daily when flower heads begin to form in the center of the plant, check its growth every day. Harvest broccoli while the tiny buds are tightly closed. If the buds begin to swell or show yellow (the flower petals), cut the head from the stem right away, no matter how small it is, because the opening buds have a mealy texture. After cutting the main head, leave the plant to grow bite-sized side shoots in the axils of the leaves. 


• Eggplant: Sort of like squash, they just tend to get bigger the longer you wait. Until they go soft.


• Squash: There is some leeway with squash. Generally anytime after they are big enough to be worth picking  but before they get too soft.


• Strawberries: Pick when red.


• Beans: The best time when to pick beans is while they are still young and tender and before the seeds inside are visibly evident when looking at the pod.


• Melon: Research of the literature (i.e. Google) tells me that you wait for the stem area to get soft.


• Kale, Spinach, Lettuce: Pick leaves sporadically as needed.


• Carrots:carrots can stay in the ground for months and keep on growing. Just  pull the carrots you need for dinner. You may as well store them in the ground as allow them to go limp in the fridge!


• Lovage: Pick when you need it. 


• Rhubarb: Pick when the stems turn red. Don't confuse with swiss chard.

Much of traditional gardening lore is based on weather and seasons. A CELSS will ideally be more consistent weather wise. The incorporation of seasons into a CELSS is a topic for another post...