i've just come in from the garden, and it's after 10pm. It's been hot the last couple of weeks, - Hot & Dry.
Now hot sunlight is good for plant growth and floriferousness, as long as there is enough water at the plant's roots, BUT here in Surrey, - we havn't had any decent rain for months (I think i've only gardened in waterproofs for 2 whole days this year!)
I am on a water meter, so I use my waterbutts whenever I can, but they've been empty for weeks. So I have had to hand water, and use a sprinkler in the evening. This evening I wanted to plant out some of the seedlings i've been growing. - I wouldn't plant any client borders at the moment, but I want to get all my seedlings in the soil before the summer holidays, - they have a slightly better chance of survival in the ground than in small pots on shelving on my patio, but to give them the best chance in the ground I set the sprinkler running on the patch I was going to plant. - Unfortunately in the 35 minutes it was running, the water only soaked down 1 cm. Not nearly enough for even a seedling's rootball (about 4-5cm deep).
So if you want plants to get the most moisture to their roots to help them survive, an overhead sprinkler isn't the most efficient way, - a watering can with a rose, or a hose with a lance spray are the best.
I teach the children in gardening club that we are watering roots, not leaves, and that they need to count their watering in Elephants. Using this method, the children can't count too quickly (one elephant, two elephants etc) and the plants get a decent amount of moisture where they need it - a tomato plant needs at least 5 elephants, the corn needs 3 elephants each. A row of seedlings needs 8 elephants. The beans 5 elephants each cane of the wigwam.
Are you using enough elephants in your watering?
A Hydrangea needs a can of water a week in this weather. Chucking it all on at once will mean most of it drains elsewhere, so a quarter of a can, then going back in 5 minutes for another quarter etc. My watering can takes over a minute to fill up from the hose (60 elephants) which means that most plants in the garden will need a minimum of 10 second/elephants spraying with a hose.
It is a lot better for the plants to drink deeply on every 2nd or 3rd day, than to have a little sprinkling every day. - Something to think about if we do start getting rain again, - has it been as heavy as 10 elephants?