When to harvest stuff

This week (the final week of my gardening course) we learnt when various vegetables are ready to harvest. Sweetcorn is ready to harvest when the tufts on the end go brown like this:

If the corns inside aren't large and juicy like you were hoping, it might have crossed itself with an inappropriate type of sweetcorn (it's wind pollinated) or there might simply be an issue with your growing conditions, e.g. the weather. You should pick sweetcorn as shortly before cooking as humanly possible.
The cauliflower below is ready to harvest. The fact it's tiny and doesn't look like a cauliflower in the shops is because I failed to put any fertiliser on it and cauliflowers are a veg that particularly needs fertiliser (a fact I learnt too late for this year's crop). A key reason for this is because you eat the flower part. To encourage a good, healthy flower head it needs potassium, but it also needs nitrogen and phosphorous as well. I also found a website that says it needs boron and magnesium too. The key point is, that much as it would be nice if it looked a lot nicer, this cauliflower is ready to harvest and eat and leaving it any longer isn't going to improve matters. That will take fertiliser when I grow them next year.

On the other hand it's too late for the cauliflower below, which not only has its own snail, it's gone beyond the point where it will taste OK - despite being even smaller than the one above.

The rather gorgeous plants below are Swiss chard (grown at the allotments, not by me):

Our gardening teacher said they taste just like spinach (irrespective of colour), but are easier to grow. You harvest these (and also lettuce) on a cut-and-come-again basis - taking outside leaves when you need them and leaving the growing shoots on the inside to keep growing. It's fine to take a whole plant if you want one though, especially after you've cut and come again a couple of times, as eventually they'll bolt (grow tall and grow flowers) and they won't taste good after that.

Runner beans ready to harvest

With beans, you just pick them when they're ready (i.e. when they look like what you'd buy in the shops). If you leave them on the plant, they will start to dry out. When they're dry you can either use them as seeds for next year's beans or as dried beans.

Hard as it is to tell, the plant above was a potato plant. You either wait until it's died off completely like this or at least until the leaves of the plant have gone yellow before you harvest potatoes. Then you just dig them up with a fork - a bit like you're digging the ground, but when you spot a potato, you just pick it out and add it to your pile.