Fully shaded garden

(Question)

My neighbour has put up a 12 emerald cedars 3 1/2ft in height on the west side of my front property line that will grow to 15 ft. I have a large 75 year old maple tree in the centre in front and a full flower garden stretching from my west property line to the maple tree and about 6 ft wide. How long will it take for these cedars to grow to 6 ft and form a hedge and then 15 ft? So eventually there will be no sun light to this garden. I have flowering full sun flowers, I have lots of tulips, 4-5 hostas which can remain, but the Anthony spirea bush (now 10 years old) would need to be moved and the other blue flox, bell flowers. I need to check what else I have in this garden. BUT it think mostly perennials that require at least 1/2 sun. Do I need to dig these up and transplant over the next couple of years? Any suggestions? It will be a lot of work. Thanks. Lorrie
416-225-5603

(Answer)

Thank you for contacting the Toronto Master Gardeners with your inquiry.

Cedars do not grow dramatically the first season that they are planted, during this time they put most of their energy into setting up their root system. Once they are properly established and planted in the right location with optimum water, sunlight and fertilizer they can grow 1 ft – 1½ ft per season.

Most perennials like your Blue Phlox  will grow well and flower in partial sun, however your bell flowers and Anothny Waterer Spirea do require full sun for best performance.

Transplanting at the right time of the year will lessen transplant shock and will increase your success. The following information is from one of our earlier posts:

Warm daytime temperatures, greater frequency of rain, shorter days, and cooler nights make fall the perfect time to transplant perennials. The key to transplanting in the fall is to plant early enough in the season to allow for proper root establishment, at least 3-4 weeks before a  hard frost.

That being said some plants transplant better in the spring and some better in the fall. And while there are exceptions, the general rule  is that if it blooms in the spring,transplant in the fall. If it blooms in the summer or fall, transplant in the spring.

Anytime a plant is transplanted it suffers some root loss which reduces the plants ability to up take water. As a result, when transplanting  it is best to cut the plants back by one-half to two-thirds to reduce transpiration (water loss).  This allows the perennials to utilize their energy towards root production rather than into supplying water.

Once transplanted make sure to apply about three to four inches of mulch around perennials. This helps to retain the moisture and keeps the ground warmer, promoting root growth well into the late fall.

You may wish to refer to the following website:  Fall’s a Good Time to Transplant Perennials

Have you considered thinning out the crown of your maple to allow more light to filter through to the garden bed below? To find a certified professional arborist to help you with a tree problem, visit the Ontario branch of the International Society of Arboriculture here.