Creating borders for the first time

Cosmos is great for height, and lavateras give shrubbiness easily. If you can find suitable colours, go for them

Personally I cheat in order to prolong the flowering period of hardy annuals. I sow a handful of those cardboard seedling pots in February, pot them on about now, and sow another handful of pots when I have the space for them. Then in late May I have some bushy plants and some strongly growing seedlings to go in, and the remaining seeds are sown between those. Much more exiting than watching empty beds for weeks to see anything happen.

The pot grown early starters need a thorough acclimatisation though.

If there are any seeds left (or Wilko's has a clearance sale...), just chuck them in in summer and depending on autumn frosts, you might get a lovely surprise around October.

It's also worth investing in some bedding plants in May when they are cheap. A fiver will give you plenty of petunias to trail over the raised beds sides, and they will blossom all summer.

Have fun!