Spring feels like planting season, and garden centers reinforce it. But in this climate, fall is measurably better, and the reason comes down to what a newly planted tree actually needs.
The case for October over April
A newly planted tree has one job: grow roots. It arrived with a fraction of the root system it had in the ground at the nursery, and until it rebuilds that, it cannot supply its own canopy through a dry spell.
Plant in October and the tree gets: soil still warm enough for root growth, months of consistent rainfall you do not have to provide, cool air temperatures meaning minimal water demand from the canopy, and an entire dormant season to establish before the canopy asks anything of it. By the time next August arrives, that tree has had roughly ten months of root development.
Plant the same tree in April and it gets a few weeks of mild weather before it has to survive a Pacific Northwest summer with a root system that is not ready. It will need watering all season, and it is far more likely to fail.
Practical window in Clark County: roughly October through November, while soil is still workable and warm enough for roots to grow. Planting can continue into winter in mild spells, but you lose some of the root-establishment advantage as soil cools.
The mistake that kills the most new trees
Planting too deep. It is the single most common fatal error, and it kills slowly enough that nobody connects cause and effect.
The root flare — where the trunk widens into the roots — must be at or slightly above finished grade. Bury it and you keep the bark of the lower trunk in constant moisture, which invites decay, and you can trigger girdling roots that eventually strangle the tree.
Critically: do not trust the soil level in the container or root ball. Nursery stock is frequently potted or balled too deep. Dig into the top of the root ball until you find where the trunk actually flares, and set your depth from that, not from the top of the soil it came in.
The hole should be shallow and wide — no deeper than the distance from the flare to the bottom of the root ball, and two to three times as wide.
Planting, step by step
- Call 811 before you dig. Free, required, and it takes one call.
- Find the root flare and measure from there to the base of the root ball. That is your hole depth.
- Dig wide and shallow, with sloping sides. Roughen the sides rather than leaving them glazed smooth.
- Handle the roots. For container stock, tease apart or cut circling roots — a root spiraling the pot will keep spiraling and eventually girdle the trunk. For balled-and-burlapped stock, remove all twine, burlap, and wire basket after the tree is positioned. Wire baskets left in place cause serious problems years later.
- Set it plumb, checked from two directions.
- Backfill with the native soil you removed. Do not amend the hole. Rich backfill in a hole of poor soil creates a container effect where roots circle inside the amended pocket rather than extending into the surrounding soil.
- Water it in to settle the soil and remove air pockets.
- Mulch two to four inches over the root zone, out to the drip line if you can — and keep it off the trunk. A mulch volcano piled against the bark holds moisture against it and causes exactly the decay you are trying to prevent. Leave a few inches of bare soil at the trunk.
- Stake only if genuinely necessary. Most trees do not need it. Trunk movement is how a tree builds strength, and permanently staked trees develop weaker trunks. If a tree will not stand on its own, stake loosely, low, and remove the hardware within a year.
- Do not fertilize at planting. The tree needs roots, not a push of top growth it cannot support.
- Prune almost nothing. Remove only broken or dead material. The old advice to reduce the canopy to compensate for root loss has been superseded — the tree needs its leaves to generate the energy for root growth.
Watering a fall-planted tree
Less than you think, but not zero. Water thoroughly at planting. Then, until the rains are steady, water deeply once a week. Once autumn rain takes over, you can generally stop.
The critical watering season is next summer, and the one after. A newly planted tree needs deep, infrequent watering through its first two or three dry seasons — slow soaking that reaches well down into the soil, not daily sprinkler passes that only wet the surface.
Right tree, right place
Before buying anything, look up and around. The most expensive planting mistake is a species that outgrows its spot.
- Overhead lines? Nothing that matures above roughly 25 feet.
- How close to the house? Consider mature canopy spread, not the sapling.
- Full sun or shade, and does the species tolerate what the site offers?
- How wet does it get in winter? Many species will not tolerate a site that stays saturated.
- Was there a tree here before, and why did it die? If root disease took the last one, do not plant a susceptible species into that soil. Worth asking an arborist about.
A tree planted in the right place needs very little from you for the next fifty years. A tree planted in the wrong place becomes a pruning obligation, then a hazard, then a removal.
Cascade Tree Works serves Vancouver, Battle Ground, Camas, Brush Prairie, La Center, Washougal, Ridgefield, and Hockinson. Our ISA Certified Arborists can look at your tree and tell you plainly what it needs. Request a residential estimate.
