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Irrigation, Soil & Fertility TimingBiofumigation Calendar
Biofumigation uses certain cover crops, mostly in the mustard family, that release natural compounds when chopped and worked into moist soil, and the timing of each step affects whether you get any benefit.
Key points
- Evidence is mixed, so treat biofumigation as one tool among several.
- Plant when the crop can grow strongly; count back from your cash crop.
- Chop finely and incorporate quickly into moist soil.
- Leave a waiting period before seeding the next crop.
- Avoid planting mustard-family biofumigants before related crops.
What is biofumigation and what can it do?
The idea is that plants such as some mustards contain compounds that break down into substances with suppressive effects on certain weeds, pathogens and nematodes when the tissue is crushed. Results in research and on farms vary a great deal by crop, variety, soil and the pest in question.
Treat it as a possible supplement to rotation and sanitation, not a replacement for a sound pest plan. Ask extension for evidence in your area before building a program around it.
Soil moisture and temperature at incorporation matter. Cool, wet soil slows the breakdown that releases the active compounds, and hot dry soil lets them escape fast. Aim for conditions in between, with soil moist and the crop chopped finely.
When do you plant the biofumigant crop?
Plant it in a window where it can grow vigorously before you need to incorporate it. In many regions that means late summer into fall or early spring, depending on whether the crop would overwinter or winter-kill. Look to your frost dates and soil temperature, since the crop must establish before cold or heat stops it.
For example, if your last spring frost usually falls in a given week, count backward from your planned cash crop planting date to see how many weeks of growth and breakdown you can fit in. If it does not fit, the crop may not be worth planting.
Crop rotation remains the foundation. A biofumigant crop works best as part of a broader plan that includes rotation to non-host crops, sanitation, resistant varieties and good drainage. Treat it as an add-on, not the whole program.
When should you chop and incorporate?
The commonly cited stage is around early to full flower, when the plant is large and the compounds are at higher levels. Chop the crop finely, and incorporate it quickly, because the compounds are volatile and escape if the material sits in the sun.
Work it in while the soil is moist, and some growers seal the surface with irrigation or a roller to hold the gases in. Avoid doing this when soil is waterlogged or when you cannot keep the surface from drying out.
Costs include seed, tillage, irrigation and the time the field is out of production. Weigh these against the benefit you can document in your own trials.
How long should you wait before planting?
Decaying residue can tie up nitrogen and release substances that affect seedlings, so there is usually a waiting period before planting. The length depends on soil temperature, residue amount and the crop to follow. Extension sources for cover crops generally advise a gap of a few weeks, but confirm for your crop and area.
A small test planting or a germination test in a pot of treated soil can reveal problems before you commit a bed or field.
What are the common mistakes?
The first is letting the crop go too far, so tissue turns woody and decomposes slowly. The second is incorporating into dry soil. The third is expecting miracles; fumigant-like effects are limited to the top of the soil and do not reach deep roots or every pest.
Some biofumigant crops can become weeds or harbor related crop diseases, so avoid them ahead of related vegetables and check seed sources. State rules and seed quality standards apply.
Which crops are used and how do they differ?
Several mustard-family crops are used, including some mustards, radishes and rapeseed types, and they differ in growth rate, cold tolerance and in how much of the active compound they produce. Varieties bred for the purpose are sold in some regions, but claims about results vary.
Ask extension which species and varieties have local trial data. Check that the seed is clean and legal in your state, and avoid anything listed as a noxious weed.
How do you evaluate whether it worked?
Treat the first season as a test. Leave an untreated strip and compare weed counts, disease incidence and crop vigor. Use consistent methods, such as counting plants in marked squares, so your numbers mean something.
Results can differ between years because soil temperature, moisture and pest pressure change. If your trial shows a clear benefit, scale it up. If not, put the time and seed into a practice with better local evidence.
Sources and further reading
Last reviewed: November 2026. Educational information, ranges only. Confirm timing with your county extension office.