Here are a few tips on how to keep flowers looking fresh and at their best in hot weather….
Don’t worry about cutting flower stems at an angle if you’re simply arranging them in a vase. It doesn’t make much difference to the flower. But a slanted cut helps if you are using floral foam; a stem with a point is easier to insert.
Use a vase that’s large enough to provide plenty of room for all the stems, with a mouth that’s wide enough to allow for good air circulation. Display the bouquet away from full sun and hot and cold drafts. If you have a choice, keep it in your coolest room.
Cut garden flowers in the morning or early evening, when the stalks are filled with water. Midday heat is stressful to plants, causing them to wither more readily when cut. Always use a sharp knife. Avoid scissors, which can pinch the water channels of the stalks. If possible, leave the flowers in a cool, dark spot for a few hours to let them stabilize before arranging.
If you want to shorten the stems on cut flowers before arranging them, cut their stems underwater; otherwise, the stem can take in too much air, causing a blockage that keeps water from the flower. (This is especially true of roses.) Floral-supply companies sell underwater cutters; or you can cut a flower in the garden, immediately submerge the stem in warm water, and cut it again in the house while holding it below the water line.
The Old Farmers Almanac