I’m trying an experiment. I have placed two large rectangular planters on my concrete pool deck and planted Boston Ivy in each. Both have the insides lined with one inch rigid insulation but I’m thinking about putting straw bales against the three exposed sides ( the fourth is against a fence) to help insulate through the winter. Any thoughts?
I’m wondering in particular if I will need to cove the straw bales to keep them dry or is I can just prop them up against the planter and remove them in the Spring?
Sounds like an interesting experiment! Over-wintering in containers can be tricky and is dependent upon the type of plant and amount of root protection during freeze and thaw cycles. One inch rigid insulation (I’m assuming it is a building grade foam or styrofoam insulation) should be more than sufficient depending on the size of container. The mature size of the plant can also be compromised by the amount of soil (volume) in the container.
Any additional protection you can give the plant roots, the better. Drainage and soil moisture prior to freeze up should be considered. The roots should not be sitting in water but the soil should be well watered prior to freezing. As far as covering with straw, it will not keep them dry but may add some protection, and if you choose this route, the straw should be removed first thing in the spring to reduce potential fungus development on the soil.
I have successfully over-wintered large cedars in containers for the past 5 years. The containers are large and insulated with 1/2″ builder’s styrofoam. I always ensure they are well-watered prior to freeze so there is moisture available for the plant roots following spring thaw. It just takes a bit more maintenance, but if you do not have space for a garden in certain locations, containers can prove helpful.
Good luck with your experiment! I am confident your ivy will thrive. Remember that once it starts to grow and affix itself to the fence (I’m assuming the containers back onto a fence of some sort), you will not be able to remove them without cutting the plant down.