Write poetry for 2 minutes no matter what you're motivation level is with no requirement for quality; anyone can write for 120 seconds with no expectations about the product.
With in 2 seconds maximum, begin an activity that you find very rewarding or enjoyable; something you love to do and do every day any how.
Do the reward activity for 10-30 minutes and then come back and write poetry for 5 minutes without expectation. Then reward your writing effort with an enjoyable activity again.
Continue this process of gradually expanding the number minutes you spend writing and then positively reinforcing the writing with decreasing time spent on the immediate reward activity. it's as simple as it is counter-intuitive.
In the case of poetry writing, I would recommend selecting reward activities that use those same psychological/creative process that poetry writing does. For example, read some poetry or literature that you just love that will get your creative juices flowing.
You may also want to rest your mind deeply before starting the writing again, so it's ready to go once you start.