Fall Garden Fertilizer in Seattle: What to Feed in October, and What to Leave Alone
An October look at what each bed gets now, how much compost a raised bed takes, and why the fertilizer waits until spring.
My soil test came back low in nitrogen this year. If there was ever a reason to reach for the fertilizer bag, that would be it. Even so, most beds should not get any fertilizer this month, and the few that do only need a little, for a few more weeks.
Fall garden fertilizer in Seattle is a different question in October than it is in June. October is mostly an amending month. Feeding gives the plant fast nutrients it can use right away, like fish emulsion, a granular organic fertilizer or a liquid feed. Amending builds the soil itself. Compost, shredded leaves and cover crops feed the soil life, break down slowly, and pay off when the beds wake up in spring. Empty and finished beds need the second one right now. Only the crops that are still actively growing need a little of the first, and only until the soil gets cold.
Why fall garden fertilizer backfires in Seattle
The days are short and the soil is cooling. The shaded West bed in my garden read 53°F on October 17. Once the soil drops below about 50°F, most plants stop doing much growing, and on a bed with nothing growing in it at all, that point has already come. Three things happen to a feed you put down then.
The plant can't use it. Organic fertilizer has to be broken down by the soil life before a root can take anything up, and the soil life works shorter hours as the soil cools. Most of what you spread then just sits there.
The rain takes it. Whatever gets released and not used washes down through the bed over five months of rain. I explained what that costs you in cover crops in Seattle. A bed of slow winter greens has hardly more roots to catch it than an empty one.
What the plant does use, it uses badly. Nitrogen in November, once the soil is cold, pushes soft, leafy growth that the first frosts damage before it can toughen up. A light feed in October, while the soil is still above 50°F, is different: crops that are still growing use it within a couple of weeks, and the new leaves have time to harden before the first frost, which usually comes in mid-November.
If your soil test came back low in nitrogen like mine, the time to fix that is spring, when the soil warms up and the plants can actually use it. In fall, compost and leaves start the job slowly, and that is all they need to do.
Not sure when it is time to feed again?I'll tell you in my emails. When the soil warms up next spring and feeding starts again, it will be in your inbox, along with what to plant, protect and harvest in Seattle as the season moves. |
Which bed gets what in October
This is the decision that matters, and it takes about two minutes per bed once you know what is growing in it.
Empty beds. One to two inches of compost, then three to four inches of shredded leaves over it. I use Cedar Grove organic compost, which is OMRI listed and has no biosolids or steer manure. The cover crop window closed around October 10, so leaves are the easier choice now. My leaf mulch post shows how to shred them so they don't mat down.
Garlic. Compost and a balanced organic granular fertilizer worked into the bed at planting, leaves on top, then nothing until spring. No bone meal on top of that. If your soil test shows plenty of phosphorus and potassium, a nitrogen-only feed like feather meal is the better choice. Mine came back with phosphorus at the top of the range and potassium high. My hardneck went into the oval bed on October 19, between the young cabbages, and that bed now gets left alone. The details are in when to plant garlic in Seattle.
Brassicas that are still sizing up. Broccoli, cabbage and kale planted in late summer are still growing, so they get a light nitrogen feed every two to three weeks while the soil stays above about 50°F. Fish emulsion at full strength, or a small amount of blood meal side-dressed and watered in. My shaded West bed was at 53°F in mid-October, so in my garden that is one more feed, maybe two, and then they are done until spring.
Young crops still getting established. Kohlrabi, chard, celery and leeks get a lighter feed, fish emulsion at half strength or compost tea, with the same rule. When the soil drops below 50°F, the feeding stops.
Onions. Leave these alone. Nothing to add.
Summer crops that are finishing. Tomatoes, squash and beans are done, and feeding them now buys you nothing. Pull them when they stop producing and put the compost where they were.
Perennial herbs. A ring of compost around them, no fertilizer. They are slowing down for winter, and they should.
Amounts, because compost is heavy and nobody wants to carry more than they need. One inch over a standard four by eight foot bed is about 2.7 cubic feet, and two inches is about 5.3. The volume is printed on the front of the bag, so do the math before you load the car. Spread it on top or rake it lightly into the top inch, then the leaves go over it.
The part that goes wrong in November
Fall feeding mistakes rarely happen in early October. They happen in November, when the greens slow down, look a little dull, and someone decides they must be hungry. They are not hungry, they are cold. From about mid-November to the end of January the days are too short for kale and cabbage to do much growing here, no matter what you put on them. A feed then does nothing for the plant and goes straight down the bed with the rain.
The other mistake comes in spring, and it is the opposite one. The first warm week arrives and everything gets fed at once, into soil that is still cold. I explained in when to fertilize vegetables in Seattle, and when to stop why a March feed often arrives in June. Feeding starts again when the soil warms and the plants start to grow. Go by the soil thermometer, not the calendar. Once the soil is back above 50°F, feeding can start again.
If you do one thing this week
Push a soil thermometer into your shadiest bed first. That number tells you whether there is one more feed left this fall or not.
Then walk your beds one at a time and sort them: empty, finished, still growing, garlic, onions, herbs. The empty beds get compost and leaves, the finished crops come out and their spot gets compost, and the herbs get a ring of compost. The brassicas and young greens get their light feed while the soil stays above 50°F. The garlic and onions get left alone. When the soil drops below 50°F, put the fertilizer bag back on the shelf until spring.
That is one afternoon and a few bags of compost, and it does more for next year's soil than any feed you could buy right now.
If you want this mapped out for everything you grow, the PNW Organic Feeding Calendar covers 72 crops month by month, with homemade and bought options, amounts scaled to your beds, and the month each crop needs you to stop. It is part of the Inner Circle for $19.99.
Want someone to walk your beds with you?
If you'd like help deciding what each of your beds needs this winter, that is exactly what a Kitchen Garden Consultation is for. I come to your garden for an hour, we walk it together, and within three business days you get a written plan for the season ahead. It is $175.
Happy fall gardening. Let me know if you need help, I'm here for you.
Jackie
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