It’s odd, but I don’t think I’ve ever seen this written down before, yet it’s a basic truth. Double flowers, ones with extra petals, tend to last longer than single flowers, that is those with the normal number of petals.
How much longer? Sometimes not at all, but usually a day or so longer, even up to a week longer. Of course, weather conditions are a factor. For many plants, even single flowers last longer when the weather is cool rather than warm and double ones do even better. Also, unseasonably hot weather can cause even double flowers to wilt or fall apart early, as can strong winds or heavy rain.
And it’s not just in the garden: it’s even more obvious indoors where inclement weather isn’t a factor. Flower arrangers know or should know that double cut flowers generally last longer than single ones.
Why? One possible reason is that so many double flowers are partially or totally sterile. The flower therefore seems to remain open a bit longer, vainly waiting for pollinisation. In other cases, the mutated plant parts that became petaloids (stamens, carpels, etc.) are just longer lasting than petals … or the flower doesn’t have a proper mechanism for shedding these abnormal growths.
Whatever the reason, double blooms do generally last a bit longer and knowing this might be a factor in your choice of plants.
It’s just something I thought somebody ought to write down!