This achievement will take roughly 1-1.5 hours.
The fastest way I can think to complete this would be to get a small flowering plant, keep making clippings until you have a bunch of them crowded into one spot, then just keep spamming X and A to quickly take as many clippings as possible while slightly moving your cursor to the areas with the most flowers. Depending on the plant, and based on my experience, this will result in about 30% of the clippings that you take will actually be flowers, the rest will be leaves or root cuttings.
Here is a very easy way to get set up for this achievement:
-Create a new free play tank
-take a few clippings of the flowering clover plants and store them in your inventory.
-now either sell all the remaining plants to clear some space, or use herbicide (it is really cheap and very fast! Just make sure the herbicide bubbles are gone before you plant your clippings)
-Plant a clipping or two, make sure to always keep spares.
-Wait for them to grow
-Take clippings from your new plant and plant them to start essentially duplicating the plant until you have like 20+
-Now go to town clipping
-if your game starts getting laggy, just use some herbicide to cull out the excess plants
Some things to note:
-You will probably get the leaf and root cutting achievements while doing this.
-The hitboxes are often inconsistent, and it may become frustrating, but just be patient.
-Your progress will automatically be saved, you do not have to do this in one sitting, you don't even need to press "Save Game", when you are ready to take a break, simply press pause, then quit the game through the xbox menu.