On the first of every month Joene sponsors GOOPs --- Gardening oops --- those mistakes we all make and are willing to confess to. I've posted many of mine.
This month I have an oops to confess, but it is also something others can learn from, as in "Don't Do That".
Don't do what I did to a newly planted groundcover. I suffocated it.
The beautiful glossy leaves on this groundcover belong to Salix yezoalpina. Salix is the willow family, and yes, it is a willow, but an unusual, low growing, spreading willow, also called dwarf pussywillow.
Although it spreads along the ground, it does have the characteristic pussy willow catkins, as this photo from empressjoan at Dave's Garden shows (mine was too new to bloom yet):
When I first got this plant, and it was still in its pot waiting to be planted, it developed a bad case of aphids. Normally I can live with aphids on my plants, I use the hose to spray them off, or wait for the birds or ladybugs to make lunch out of them.
But this pot was heavily infested, and since it was still in a flimsy plastic pot, a strong jet spray from the hose would have sent it flying. So I reached for the spray bottle of horticultural oil. That gets rid of aphids and other soft bodied bugs by smothering them in a coat of oil. It completely took care of the problem.
It's safe. It is not a chemical pesticide, it is simply a viscous mineral or vegetable oil with an emulsifying agent to help it stick.
There is a heavy version that you use in winter when plants have no leaves, and it coats the larvae on stems and bark. That's called dormant oil, but it is too heavy to use in summer. It smothers everything, including the openings on foliage that the plants need to respire. So you only use it in winter when there are no leaves out.
The lighter oil, called summer oil, or superior oil, can be sprayed on foliage, and that's what I used.
The lighter hort oils still block the openings on the leaves somewhat, but the plant is not really affected unless temperatures get into the 90s and hot sun stresses the respiration of the leaves.
Guess what our temperatures were. Guess how much sun these plants got when I finally put them in the ground.
Do not ever use hort oil on plants that are in full leaf if it is going to be very hot and sunny. Do not water them heavily, increasing their desperate attempt to move water through the clogged leaves.
Do not overspray and saturate everything in the belief that more is better.
I cut off the dead leaves, and new foliage is beginning to grow out now. From here on, I promise not to spray hort oil on leaves, water heavily, and set any plant out in summer sun and temps ever again. I learned a lesson.