Monday tops out near 88°F, then Wednesday brings roughly a quarter inch of rain and the first 70°F high since June. Every task below is timed to that shift.
This Week's Action List
- 1
Direct sow spinach, mache, and arugula Tuesday evening or Wednesday morning to let the 0.24 inch rain do your germination watering. Soil temperatures in the top inch are finally dropping under 75°F, which is the ceiling above which spinach seed goes dormant. Bloomsdale Long Standing and Winter Giant mache are the reliable picks for overwintering harvests through February.
- 2
Container shrubs planted this week get a nearly perfect establishment window. Cooler soil, three separate rain days from Wednesday through Friday totaling roughly 1.18 inches, and no forecast heat means roots will push before dormancy. Water each root ball in deeply at planting, then let the sky handle the rest through Saturday.
- 3
Late blight risk peaks Wednesday and Thursday, when highs in the low 70s combine with 73 to 89 percent rain probability and overnight lows in the mid 50s. If you see brown greasy lesions on tomato leaves or dark stem cankers, pull the whole plant, bag it, and put it in the trash, not the compost. Harvest every blushing tomato Tuesday afternoon before the weather flips.
- 4
Rake fallen rose leaves this week and get them off site. Black spot spores overwinter on that debris and reinfect new growth next April, so every leaf pulled now is one less lesion in spring. Do not compost them, and do not prune the canes themselves; structural rose pruning waits until February.
- 5
Cut fertilizer to zero on all woody shrubs and trees starting Monday. Any nitrogen push now drives soft growth that will not harden before the first frost around October 15, and soft tissue is what freezer burns in November. Dahlias and annuals are the exception: keep them fed with a low nitrogen, high potassium formula to push blooms until frost.
- 6
Plant garlic cloves between September 5 and September 30 for the best root establishment before dormancy. Music, German Extra Hardy, and Chesnok Red are the hardneck varieties that consistently size up in Portland clay. Plant cloves pointy end up, two inches deep, six inches apart, in a bed amended with two inches of compost.
- 7
Check dahlia foliage Thursday morning for the first signs of botrytis: fuzzy gray mold on spent petals and water soaked spots on stems. The Wednesday rain plus mid 50s overnight temperatures is textbook botrytis weather. Deadhead spent blooms into a bag, not onto the soil, and thin any crowded interior stems for airflow.
- 8
Clear rain barrel overflow diverters and downspout screens by Tuesday afternoon. Wednesday's storm is the shoulder season shot across the bow, and Friday could deliver another 0.81 inch. A blocked diverter sends roof water straight into the foundation, which is a much bigger problem than a full barrel.
- 9
Order tulip, daffodil, and allium bulbs this week for October planting. The reliable Portland performers are species tulips like Tulipa clusiana, any daffodil in the Narcissus poeticus or jonquilla groups, and Allium christophii for structure. Skip hybrid tulips unless you plan to treat them as annuals; wet Portland winters rot them out by year three.
Frequently Asked Questions
When should I stop watering my vegetable garden in September?
Do not stop yet. Fall crops sown this week need consistent moisture for germination, and established tomatoes and peppers still finishing fruit need roughly an inch of water per week. Cut irrigation frequency by about 25 percent from peak July levels, then reassess in late September once the rain pattern stabilizes.
Is it too late to plant fall vegetables in Portland in early September?
For direct sown spinach, arugula, mache, cilantro, and Asian greens, the first week of September is still solidly in the window. For broccoli, cabbage, and cauliflower, you needed transplants in the ground by August 15, so it is too late to start those from seed. Garlic planting runs from September 5 through the end of the month.
Why should I not prune shrubs in Portland in September?
Pruning stimulates new growth, and any tender growth pushed in September will not harden off before the first frost around October 15. That soft tissue then dies back and creates entry points for winter fungal diseases. The structural pruning window for most woody plants opens in November when they are fully dormant.