Portland fall shrub planting season opens this week, and the forecast is doing you a favor: cool nights in the low 50s, warm soil still in the 60s, and no rain until at least next weekend. That means dig now, water deeply, and let October's rains take over the watering job for you.
This Week's Action List
- 1
Rhododendrons, camellias, and azaleas set out this week root fastest when the planting hole is twice as wide as the root ball but no deeper. Backfill with native soil, not amended soil, or the roots will circle the hole like a container.
- 2
Wednesday's forecast high near 89°F will stress anything planted Tuesday or Wednesday afternoon. Plant in the morning before 10 a.m., or wait until Friday when highs drop back to the mid 70s.
- 3
New shrubs need 2 to 3 gallons of water at planting and another 2 gallons twice a week until steady rain returns, usually mid to late September. Do not trust a light sprinkle to soak a fresh root ball.
- 4
- 5
This is also the week to rake up every rose leaf on the ground and bag it for the bin, not the compost. Black spot spores overwinter in fallen leaves and reinfect new growth every March, so fall cleanup is the single highest payoff disease step of the year.
- 6
Garlic goes in between September 20 and October 10 in Portland, so use this week to prep the bed: pull spent summer crops, work in 2 inches of compost, and let the bed settle before cloves go in next weekend.
- 7
Hold off on any structural pruning of trees and shrubs until November dormancy. Cuts made now push a flush of tender growth that will not harden off before the first frost around November 15.
- 8
Watch dahlias for gray fuzzy patches on petals and stems after this weekend's cool damp Sunday night. Botrytis moves fast once September nights drop into the mid 50s, so pinch off any mushy blooms and toss them in the trash.
Frequently Asked Questions
Is September really the best time to plant shrubs in Portland?
Yes. Soil temperatures stay in the 60s through October, which lets roots establish while the tops are going dormant. Winter rains handle most of the watering, so fall planted shrubs enter next summer with a root system twice the size of anything planted in spring.
How much should I water a newly planted rhododendron in September?
Give 2 to 3 gallons at planting, then 2 gallons twice a week until reliable rain returns. Once weekly rainfall passes half an inch, you can back off, but check the root ball with a finger, since bark mulch can hide a bone dry root zone underneath.
When exactly should I plant garlic in Portland?
The sweet spot is September 20 through October 10 for hardneck varieties like Music, German Red, and Chesnok Red. Plant cloves 2 inches deep and 6 inches apart, then mulch with 3 inches of straw once the ground cools in late October.
Can I prune my rhododendrons and camellias in September?
No, not for shape or size. Next spring's flower buds are already set, and any cuts now will remove bloom and push soft growth that frost will kill. Limit September work to snapping off obvious deadwood and save real pruning for right after bloom in May.