What are the best cut flowers to plant to have all summer long

Zennias are great for this. I plant them from seeds in early May (in Ohio). Thin them to about 4" apart when they are about 4-5" tall and let them grow. They love lots of sun. Water at the base or they get powdery mildew on the leaves later in the summer. It doesn't hurt them but they look better without it.

Cosmos !

http://www.hgtv.com/outdoors/flowers-and-plants/flowers/20-flowers-for-a-cutting-garden-pictures

Roses are great for blooming all summer. They love lots of sunshine and we mulch ours and feed them banana peels (potassium) and get lots of blooms. Geraniums are also great perennials that bloom all summer. Annuals that bloom all summer are petunias and sweet williams.

depends on your location - but I love Zennias -- come in all sizes/color ( except blues/purples ) - are susceptible to powdery mildew - need good ventilation - don't over crowd them!

Vinca’s love the sun and grow all summer long, as long as you keep them watered ! I plant mine in pots and they just keep blooming!

Iris, Gladiolas, & Tiger Lilies are terrific for full sun gardens.

Roses, sunflowers, carnations - here are more!

http://www.hgtv.com/outdoors/flowers-and-plants/flowers/20-flowers-for-a-cutting-garden-pictures