How long should I wait between fertiliser application and harvest?

Applying nitrogen very close to harvest is usually wasteful and can even harm quality and timing. By late in the crop, the plant is moving into maturity and grain or fruit filling, and pushing in extra nitrogen then can delay maturity, encourage soft late growth, invite pests, and in some cases lower produce quality, while much of the late nitrogen is simply not taken up. The useful window for nitrogen is during active growth and the run-up to the main demand stage, not the final stretch before harvest. So if you are already close to harvest, a late nitrogen dose is unlikely to help and may set you back. The better fix is to plan your splits earlier next season so the crop has enough nitrogen during its high-demand period. For the specific cut-off stage for your crop, check with your KVK, base your dosing on your Soil Health Card or soil test, and do not over-apply.