Try mulching with straw and keeping the roots warm during the cold months. They need lots of sun. I have read an old method of making your Rhubarb grow longer and it worked for me. Get a dark container (an old pot so it fits over the rhubarb plant) when you see first signs of plant growing cover plant completely. In the dark they seem to want to grow. Check from time to time. If you have a container with a lid on it cut the bottom out and put over with lid on top when it is nearly at the top take the lid off and it will continue to grow longer. I have comfrey growing next to mine and throw the spent leaves next to Rhubarb to help with fertilising. Hope this helps.
Try mulching with straw and keeping the roots warm during the cold months. They need lots of sun. I have read an old method of making your Rhubarb grow longer and it worked for me. Get a dark container (an old pot so it fits over the rhubarb plant) when you see first signs of plant growing cover plant completely. In the dark they seem to want to grow. Check from time to time. If you have a container with a lid on it cut the bottom out and put over with lid on top when it is nearly at the top take the lid off and it will continue to grow longer. I have comfrey growing next to mine and throw the spent leaves next to Rhubarb to help with fertilising. Hope this helps.