There's a lot of advice out there about making flowers last longer. Aspirin in the water. A copper coin. A drop of bleach. Some of it helps, some of it is folklore, and most of it misses the basics. The basics are what actually make the difference.
Here's what genuinely works, without the mythology.
Start with a clean vase
This sounds obvious but it's the step most people skip. Bacteria in a vase, leftover from a previous bunch, will kill new flowers much faster than they need to go. Before you do anything else, wash the vase with hot soapy water, rinse it properly, and start fresh.
If you're reusing a vase that's had flowers in it recently, a quick rinse with diluted bleach, about a teaspoon per litre followed by a thorough rinse, will clear any residual bacteria. It takes two minutes and it makes a real difference.
Cut the stems properly, and keep cutting
When you get flowers home, cut at least two or three centimetres off the bottom of each stem before putting them in water. Cut at a 45-degree angle to increase the surface area and help the flower drink more.
The bit most people miss: do this cut under running water, or with the stem submerged. Air bubbles in the stem block water uptake, and cutting in air lets those bubbles straight back in. A sharp knife or clean secateurs work better than scissors, which can crush the stem tissue.
Every two or three days, give the stems another fresh cut. It sounds like a small thing and it genuinely isn't.
Water temperature matters
Most cut flowers prefer room temperature water. Cold water slows water uptake, which is why flowers can look limp even when the vase is full. The exception is spring bulbs like tulips, which actually prefer cool water.
Change the water every two days. The little flower food sachets that come with florist bunches genuinely work. They contain sugars for energy, an acidifier to help absorption, and a bactericide to keep the water clean. Use them. If you don't have any, a teaspoon of sugar and a few drops of white vinegar does a reasonable job.
Things to keep flowers away from
Direct sunlight speeds up ageing. A bright room is fine but a windowsill in afternoon sun is not.
The fruit bowl is a surprisingly common flower killer. Ripening fruit releases ethylene gas, which causes flowers to age faster. Bananas are especially bad for this. Keep the vase away from the fruit bowl.
Heating vents and draughts dry out petals faster than almost anything else. In winter especially, the coolest, most stable spot in your home is where your flowers will do best.
Reviving flowers that are starting to go
If flowers start to wilt before their time, cut the stems and place them in a bucket of warm water up to their necks somewhere cool for a few hours. They'll often recover fully.
For roses with drooping heads specifically, re-cut the stem, wrap the whole flower including the head in damp newspaper, and stand it in water overnight. It sounds strange and it works.
Some flowers just won't come back once they've turned. When that happens, strip the spent blooms and rearrange what's left. Three flowers that are still beautiful are better than five that have given up.
The short version
Clean vase. Fresh cut done under water. Room temperature water changed every two days. Away from heat, direct sun and the fruit bowl. Do those things consistently and your flowers will last significantly longer.
And if you want flowers that start stronger from the beginning, buy seasonal. In-season flowers are fresher at the source, travel less, and arrive closer to their peak. From the garden to your door.