Q.rock roses
I planted my rock roses seeds in march and only one has come up. Why is that?

Did you sow these seeds indoors?
What is your growing zone?
If you are in zones 8-11 you can direct sow your seeds outdoors after danger of frost.
If you are in a colder zone, 7 or lower, you would need to either wait until frost danger has passed or start indoors.
There are many reasons for lack of seeds germinating.
Did you seeds come in a seed packet? A seed packet generally has all the germination information needed.
Make sure you used a soil less seed medium to start your seeds.
These links have more information.
https://www.gardeningknowhow.com/garden-how-to/propagation/seeds/soilless-seed-mix-info.htm
https://www.gardeningknowhow.com/garden-how-to/propagation/seeds/when-to-start-seeds.htm
https://www.gardeningknowhow.com/ornamental/shrubs/rockrose/how-to-grow-rockrose-shrubs.htm