In May, weather forecasts can change every day. 2° can suddenly become 12°. This year we had a long spring, with beautiful sunny days, but cold nights. Even after the Ice Saints' days there were still mornings when the grass crunched.
4° may sound safe enough to finally plant all those courgettes, cucumbers, peppers and tomatoes, but it's better not to do this anyway. The soil can still freeze at 4°. I don't know if it was a coincidence, if I just paid more attention to it this year, but I have rarely seen as many pictures of runted plants as this year.
But yesterday I couldn't resist any longer, the sun was shining as intensively as all previous days and the good weather conditions made it impossible for me to concentrate behind my laptop. All courgettes, pumpkins and tomatoes were moved from their pots to the wide world.
The last few days and weeks I have been preparing them for this moment. Every morning they were taken outside and every night they were moved back to the conservatory. This way they can gradually get used to the outdoor conditions. Even if your plants come from a garden centre, this is the best approach as these plants are grown in ideal conditions with plenty of light, sufficient water and the right fertilization. These are conditions that probably contrast with your vegetable garden where it can be hot and dry one week and wet and cold the next week. After a few days they will be ready to be planted out. They may look miserable at first, but they will soon recover and create new leaves.
Before you put the plants in the soil, put them in a container with water to allow the root ball to suck itself full of water, make the planting hole sufficiently large and add some extra compost if you haven't already done so.
I usually leave the soil between the plants exposed for the first few days, this way it can absorb the heat generated by the sun during the day and release it again at night. But after a few days I cover the soil between the courgettes and pumpkins with a thick mulch layer, which prevents dehydration, inhibits weed seeds from germinating and keeps the fruits clean. Straw, grass clippings or other plant debris are all suitable options for this.