What do I do if I have already spread contaminated manure?

Confirming it, deciding between removal and waiting, what you can safely grow in the meantime, and the honest timescale for the bed coming back.

Difficulty: intermediate
Time: 1 hr 30 min
Read: 5 min
Safety: warning

Short answer

Confirm with a bean test on soil from the bed. If the manure is still sitting on the surface and has not been dug in, scrape it off — that removes most of it. Once it is incorporated, removal is impractical: keep the bed warm, moist and cropped with unaffected plants such as sweetcorn, onions, leeks and brassicas, which keeps soil life active and speeds breakdown. Expect one to three years, and retest each spring.

Do this first

How do I test manure or compost for weedkiller before I use it?

Discovering this in June, with a bed of ruined tomatoes, is genuinely disheartening, and there is no clever fix. What there is: a way to confirm what you are dealing with, one window in which physical removal is worth doing, a sensible cropping plan for the affected ground, and a realistic timescale so you are not testing hopefully every fortnight.

Safety

There is no product that neutralises aminopyralid or clopyralid in soil and none should be sold to you as one. The residue breaks down through soil microbial activity over one to three years and nothing available to a gardener reliably speeds that up by much. Treat any claim to the contrary with suspicion, and do not compost the affected crop residues back into the same system.

What you'll need

Bean seed and pots for confirming the diagnosis
A spade or shovel if the material is still on the surface (optional)
Seed for unaffected crops — sweetcorn, onions, brassicas (optional)
Compost or leaf mould from a clean source

Step by step

Confirm it before you act.Take soil from the affected bed at rooting depth and run the same three-pot bean test against a control of trusted compost. Frost damage, virus, aphid damage and drift from a neighbour's weedkiller all mimic the symptoms, and the responses to those are completely different.
Establish how far it went.Test soil from each bed the material was spread on, separately. Very often only part of the plot was treated and the rest is fine, and knowing that changes the whole season's plan.
Scrape it off if it is still on the surface.This is the only window where physical removal works. Manure or compost mulched on top and not yet incorporated can be lifted with a shovel, and doing so removes the great majority of the residue. Move fast — once worms have taken it down, this option is gone.
Do not attempt to remove incorporated material.Once it is mixed through the top 150mm, excavating the bed means removing and disposing of tonnes of soil, and the disposal itself is a problem. It is not proportionate, and the waiting option gets you to the same place.
Dispose of scraped material and affected plants properly.Do not put it on the compost heap — you will simply move the problem into next year's compost. Spread it on a lawn, on paths or around established trees and shrubs, where grasses and woody plants are unaffected and it will degrade in place. Do not give it away without saying what it is.
Keep the soil warm, moist and biologically active.Degradation is done by soil microbes and it needs the conditions microbes like. Mulch with clean compost or leaf mould, keep the bed from drying out, and keep something growing in it. Bare, cold, dry soil degrades the residue most slowly.
Crop it with plants that do not care.Sweetcorn, onions, garlic, leeks, brassicas of every kind, and grasses all grow normally in contaminated ground. A season of brassicas and alliums keeps the bed productive, keeps roots and soil life working, and costs you nothing.
Retest each spring before planting anything susceptible.Same bean test, soil from the bed. Do not judge by how last year's crop looked — a mild residue can still distort tomatoes while everything else appears fine. Test until it comes back clean twice.
Trace the source and report it.Go back to the yard, farm or supplier with what happened. Most have no idea, and the information is what stops the next load going to another gardener. If you bought it from a commercial supplier, that is a straightforward consumer complaint.

Tips

Turning the soil once, early, does help a little by exposing more of the residue to microbial contact and to air. Beyond one pass it is not worth the structural damage.
Adding fresh compost, leaf mould and other clean organic matter feeds the microbial population doing the breaking down. It is the closest thing to an accelerator there is, and its effect is modest.
Home compost heaps that have taken affected crop residues, straw or hay carry the residue forward. Keep affected material out of the heap entirely for the duration.
Charcoal and biochar are sometimes suggested as binders. There is no reliable evidence at garden scale, and the practical effect is to lock residue up in a form that may release later. Time remains the answer.
Growing in containers of clean bought compost keeps the tomatoes and potatoes coming while the bed recovers. It is the pragmatic response to losing a season.

If it doesn't work

Only some plants in the bed are affected

Cause: Uneven spreading, or a mixture of susceptible and unaffected species — Fix: Test soil from the affected and unaffected ends separately. Patchy contamination is common and you may only need to write off part of the bed.

Bed tested clean last autumn, tomatoes distorted again this June

Cause: Autumn testing in cold soil with slow-growing beans reads falsely clean — Fix: Test in warmth — a windowsill in spring, not an unheated shed in November. Slow growth hides mild distortion.

New compost from your own heap is now causing distortion elsewhere

Cause: Affected crop residues or contaminated straw went onto the heap — Fix: Stop using that compost on susceptible plants, test it, and keep affected material out of the heap. Use the batch on lawns and around shrubs.

Questions people ask

How long until the bed is usable again?

One to three years in most reported cases, at the shorter end in warm, moist, biologically active soil and the longer end in cold, wet or poor ground. Retest each spring rather than counting seasons.

Should I dig it out and replace the soil?

Only if the material is still sitting on the surface and can be scraped. Excavating an incorporated bed means moving tonnes of soil to no better outcome than waiting, and you still have to dispose of it somewhere.

Can I claim compensation?

If you bought the material from a commercial supplier, it was not fit for the purpose it was sold for, and normal consumer rights apply — raise it with the seller in writing. Manure given away free by a livery yard is a different matter and usually a conversation rather than a claim.

Will it affect my fruit trees or my lawn?

Lawns and grasses are unaffected — that is what the chemical is designed to spare. Established fruit trees and shrubs are far less sensitive than annual vegetables and generally come through unharmed.