Each week, Susan Richards of New North Greenhouses answers your gardening questions. Have questions about your gardening needs? Please email her at firstname.lastname@example.org.
Clare: I have a huge hosta plant that is crowding out the other plants around it. Can I move or divide it right now?
That's the beauty of perennial plants. They can be moved or divided when they outgrow their space in your garden. However, summer isn't the best time of year to do that work. Early spring before new growth really gets going or mid fall once the foliage starts to die down are the best times.
The general rule of thumb is to divide a perennial opposite it's bloom time: fall bloomers are done in spring; spring bloomers in fall and summer blooming plants can be divided either time.
It's stressful for a plant to be divided or moved when in bloom. They are exerting so much energy to produce flowers and seeds that little energy is diverted to growing new roots. If Aunt Martha comes to visit, sees your stunning phlox in bloom and just has to have a piece, be sure to cut off all the blooms first before dividing. You can put the cut stems in a vase and enjoy the flowers indoors!
So the answer to your question, Clare, is to divide and move you monster hosta in mid to late September. Once the leaves start changing colour you know the plant is shutting down for the season and the job can start. Be sure to use transplanting fertilizer when replanting to help stimulate new root production.
Ben: What insect is attacking my cedars? There are large sections that have died, turning rusty brown.
That isn't an insect problem. The stress of the severe winter we had has caused some sections of cedars to die. I noticed the same thing as i drove through town last week. It was mainly on Emerald Cedar, which is the variety that is just hardy to our area but doesn't do well further north.
Last winter temperatures dipped so low, for such a long period of time, that many zone 4 and 5 plants really suffered.
All you can do is cut out the dead areas then reassess. Is the cedar worth keeping in the garden? It will take several seasons to fill in bare areas, if it happens at all.
Wendy: I found a slimy black slug-like insect on the back of the leaves of my shrub. What is it?
That is a pear slug. They eat the back of the leaf and the top tissue turns brown and dies. Normally, this will not kill a healthy plant.
You can spray pear slug with insecticidal soap.