20th June is the longest day this year bringing extra sunlight hours (and perhaps warmer weather).
Gardens will be full of flowers and the veg gardens producing lots to harvest, but the weeds will be having a merry time as well and need to be kept in check.
Earth up potatoes as the grow, first early potatoes can start to be harvested (normally about 10 weeks after planting them). Pinch out side shoots of tomatoes, you can pot these side shoots up to have even more tomato plants. Start to feed them once the first truss is setting fruit. Check roses for signs of pests and disease.
Stake any herbaceous perennials that might flop over and be damaged. Trim evergreen hedges, but check for nesting birds first and wait until they have fledged.
Keep dead heading summer bedding, early flowering perennials and repeat flowering roses to encourage more flowers. Cut back leaves of spring bulbs once they have started to turn yellow.