Hello from downtown Toronto.
My “garden” is a terrace on the 21st floor. it faces north but gets lots of hot afternoon sun in the summer. Last year, I planted a Canadian serviceberry in a 28x24x27H insulated planter with mulch top.
In the spring, it looks lush and healthy but not so much now. Yesterday, many of the leaves started to show deep brown lines as you can see on the photos. Is this the result of the heat and lack of water? How can this sad state be fixed?
Thank you for contacting the Toronto Master Gardeners. From the image that you posted I suspect that your serviceberry is suffering from too little water in the very hot weather that we have been having. Growing on a 21st floor terrace, is challenging situation for the shrub. You have been taking the right steps in growing it in a large planter and mulching the soil surface. However you should also be checking regularly to make sure that the soil is consistently moist (not wet) and well drained; your container should have drainage holes to ensure that the roots are not sitting in water. You could consider getting a moisture meter to check the moisture in your soil.
As well, although a serviceberry grown in the ground will generally be able to satisfy its all of its nutritional needs from the soil, if grown in a container you will need to fertilize on a regular basis (at least annually). Look for a slow release fertilize suitable for container grown trees and shrubs and apply at the times and quantities directed.
If you serviceberry has been suffering from drought, it should recover once it is regularly watered; it may even grow replacement leaves this year.