Why can't I grow rocket from seed? And other lessons from the garden

Every year I have tried to grow rocket from seed I have struggled, except for two. Last year, rocket self-seeded itself everywhere and grew up from under the dead stalks of the old plants. This was not ideal, as it grew exactly where I'd had it last year and not where it needed to be in my new crop rotation. So I thought that this year I'd sow a lot of seeds and in case my problem was slugs and snails, I'd use a copper slug ring to keep the slugs away. The other thing I did differently was that I actually remembered to water my seeds most days. Well, it turns out my issue was (probably) not slugs. The rocket grew as well outside the slug ring as it did inside it. Also, I have far too many seedlings, so although I think sowing three times as many seeds as you want is I good idea, especially for difficult plants that are tricky to germinate, I actually overdid it with the thick sowing. I'm going to have to thin them soon. What really made a difference to growing rocket from seed was watering with plenty of water on most days when it didn't rain. The same trick also worked wonders on my turnips, kale and onions.

Onions' first leaves

It is yet to have an effect on the carrots or leeks. I am hopeful that I may have the very first signs of chard, beetroot and lettuce growing, though, and not just weeds flourishing in their rows.
It has also had no effect on the asparagus or the raspberries, for the reason that it didn't occur to me to water them, but they're putting up shoots again anyhow.

Another lesson learned is that I need to pay more attention to watering my sweet corn seedlings in particular and all my seedlings in general. Also, some varieties are more tolerant of poor watering habits than others. First I overwatered my sweet corn seedlings, then I left it too long between waterings because they still looked quite damp. They weren't. This year's variety, Gold Crest, promptly died off and my belated watering was too little too late. They have now gone to the compost heap.

On the other hand, my Incredible F1 sweet corn that I saved from last year's crop is still growing strong, despite me subsequently going back in the opposite direction and overwatering the plants again.

The lessons I learned from this are:
1. Some varieties of sweet corn are more tolerant of early neglect than others, if you're not going to water properly, sow Incredible F1.
2. Check the soil for dampness with your finger. Appearances are deceptive.
3. It's looking like you can save last year's sweet corn for seed (although I'll need to see the plants produce tasty sweet corn for my final decision).
Also, because when I've previously planted cucurbits in March my plants got too big and started drooping out of their pots and damaging their stems before it was time to plant them out, I decided this year to wait until April to plant my courgettes and squash. I will also be taking some measure to protect them from slugs when I do plant them out, after last year's fiasco. I can't afford for the seedlings to be eaten in their entirety this year, as I have no spare seeds because of a storage problem. I keep my seeds in paper envelopes in plastic bags divided by crop type, so I can find them more easily.

This year, the cucurbit bag got some sort of mite all over it. I decided to dust it off the seeds and plant them anyway, as the mite seemed not to have damaged the seeds, but I threw all the remaining seeds, envelopes and bags out to stop the mite from spreading. I've also put the box of seeds back in a different place from where I was previously keeping it.

I'm not sure what lesson to take away from this. Did my plastic bags cause the problem by providing ideal breeding conditions? Or did they prevent the problem from spreading and causing more damage? I'm going to carry on with the same method for now and see if I get any more problems.
Another thing I've decided to do this year is repot at an earlier stage, so that my seedlings don't end up with their roots all tangled together and with too many in a pot for optimum growth. I've now repotted several of my tomatoes leaving a maximum of two to a pot. I've also repotted my kohlrabi, so fewer are sharing each pot. I was planning to plant it out already, but it's been so cold recently, it's never felt like the right time to take it out of the greenhouse to harden it off.

My broad beans are doing well so far this year. They seem happy in their partial shade environment and haven't yet succumbed to much slug damage or to black fly. I'm pretty sure the black fly is coming. It's been their constant companion every year I've grown them so far. I'm simply going to have to check them regularly, wipe the black fly off and maybe use a mix of water and a dash of washing-up liquid to spray them with. The Internet also says I should nip off shoot tips to encourage the beans to ripen. I have hope that this year I've finally planted enough of them to get a decent crop. They've always cropped very badly for me in the past, possibly because of my failure to treat their black fly early enough (or in some cases, at all).

Overall, the garden is looking good and ready for another year of vegetables.