I wish I had a nickel for every time I’ve heard, “Rhododendron won’t grow up here.” While Zone 5 is not friendly to many rhododendrons, there are literally dozens that are cold-hardy for our Chicago winters.
They may expire over the winter but almost certainly they are already weakened from other cultural factors. The cold is just the final cause, but not the primary reason for their death.
The problems with hardy Rhododendron are generally related to soil and location in the Chicago area. Rhododendrons don’t like heavy clay or a high soil Ph and we have both. They also don’t like desiccating winter sun and wind.
So if you have Rhododendron in soil that is not amended and they are on the south side of your home the chances of success are nil.
There are four keys to successfully growing Rhododendron this far north:
- East and North facing walls are best. Rhododendron need shade in both summer and winter. As the winter sun gets higher in the sky during February and March the plants dry out and cannot take in water. The sun cooks them mercilessly when they are sited wrong.
- Amend the soil with organic matter such as leaf compost, bark fines, and sand in combination. Mushroom compost on its own is not satisfactory. I normally use 50% topsoil, 20% leaf compost, 20% bark fines and 10% sand as a planting medium.
- Till the organic matter deep and dig wide holes. Just backfilling into a small planting pit is a no-no.
- When you are installing the plants make sure the top of the root ball is perhaps an inch above grade. Rhododendron do not like wet feet. Planting height works hand-in-hand with the soil amendments to create a good drainage platform for the plants.
Last year I drove by a project that I completed in 1999, where I had installed a block of about 25 Poukhanense Rhododendron (Rhododendron yedoense var. poukhanense) and they were absolutely performing like gangbusters. They had grown to about 3 feet and co-mingled into a beautiful mass of lavender blooms. They have not lived that long by magic. They were near a forest preserve on the north face of the home in a soil mix similar to what I described earlier.
Rhododendrons are viable in our Chicago landscapes. They can be the all-stars in your landscape. It just takes a little time and effort to enjoy those magnificent spring blooms.
Pictured below: (Rhododendron ‘Karen’) Karen Azalea