Seeding cover crops: timing, mixtures and drone seeding compared

Hardly any job on the farm gets pushed back as often as cover crop seeding. The harvest drags on, the soil is too wet or too hard, the machinery is somewhere else — and suddenly it is mid-September and the mixture that was supposed to fix nitrogen and root through the soil never gets past ten centimetres.

Yet growing cover crops is one of the few field operations where the return depends almost entirely on the calendar. This article sorts out the three questions that decide it: when you seed, what you seed and with what.

1. The timing decides everything else

A cover crop builds biomass through heat sum and day length. Both decline daily from midsummer onwards. The practical consequence: every week you seed earlier gives you more root mass, more fixed nitrogen and more soil cover — and disproportionately so, not linearly. A seeding in early August and one in mid-September are not "four weeks apart"; they are two completely different stands.

There are three realistic time windows, and each has its own method:

2. The mixture: rotation first, catalogue second

The most common source of error in cover cropping is not the mixture itself but the fact that it was bought for the wrong rotation. Three rules that avoid most of the problems:

Crucifers and oilseed rape do not get along

Mustard and oil radish are crucifers — just like oilseed rape. Placing them before or after rape in the rotation increases the pressure from clubroot and related diseases. In rape-heavy rotations, better switch to Phacelia, niger, buckwheat or legumes.

Before sugar beet, only nematode-resistant varieties

Oil radish and mustard are available in nematode-resistant varieties that actively reduce the population of the beet cyst nematode instead of multiplying it. Before beet this is not a nicety but a must — and the price difference in the seed is a rounding error against the potential yield loss.

Frost-killed or winter-hardy — a decision about next spring

Frost-killed species (mustard, Phacelia, niger, buckwheat, sunflower) save you the termination in spring and suit follow-on crops that clear the field early. Winter-hardy stands (winter rye, winter vetch, clover-grass, Landsberger mixture of vetch, ryegrass and crimson clover) keep the soil covered all winter, root deeper and provide fodder or mulch in spring — but cost you an operation to terminate them. Incidentally, in mild winters like those around Lake Constance, "frost-killed" species do not always die off reliably; that belongs in the planning.

As a rough guide for pure stands and how they behave from the air:

The figures are guide values for pure stands and do not replace the recommendation of your seed supplier — site, variety and seeding date shift them considerably. Ready-made mixtures usually lie between 25 and 40 kg/ha depending on their composition.

3. Drone seeding, seed drill or spreader — an honest comparison

We fly drone seeding as a contractor. Still: the drone is not a better seeder, it is a different method with different strengths. Anyone who uses it where the drill would be better ends up dissatisfied.

In short: on a dry, trafficable 20-hectare field after harvest, the seed drill is hard to beat. The drone plays to its strengths where soil, crop or calendar make driving impossible — in pre-harvest seeding, on wet ground that will not carry, in small-scale or sloping terrain, and whenever your own machinery is tied up in the harvest and the time window is closing.

4. Five things that decide the success of drone seeding

1. Fly before the rain, not after. Seed on a dry surface does not germinate. The best day for the job is the day before a forecast period of rainfall — which is why we schedule drone seeding at shorter notice than other operations and keep dates free for it.
2. Raise the seed rate by 10 to 20 percent. Broadcast seeding without seed-to-soil contact has a lower field emergence than seed placed in the soil. That is not a disadvantage of the drone but of the method — and it can be budgeted for.
3. Spread the straw evenly. With pre-harvest seeding, the chopped straw is your seed cover. Poorly distributed straw mats smother emergence in patches — a matter for the chopper setting, not for the drone.
4. If possible: roll. A pass with the roller or a shallow straw harrow after harvest lifts field emergence noticeably. With pre-harvest seeding this is not an option — there you work with the residual moisture under the crop instead.
5. Delineate the field cleanly beforehand. We fly according to the drawn area. The more precise the boundary, the less seed ends up in ditches, tracks and neighbouring fields. You can upload field files from FIONA, iBALIS or as a shapefile directly.

Frequently asked questions

What is the latest date for seeding cover crops?

As a rule of thumb, mid-September. After that, the heat sum is no longer sufficient for most species to build a stand that binds nutrients and roots through the soil. If you are later than that, switch to fast-starting species such as mustard or niger — or to a winter-hardy green cover that catches up in spring. Separate, earlier cut-off dates apply to autumn fertilization and funding programmes.

Do I have to roll after drone seeding?

If you can: yes. Drone seeding is broadcast seeding onto the surface; it lacks the seed-to-soil contact of drilling. A roller or a shallow straw harrow improves field emergence considerably. With pre-harvest seeding into the standing crop this is not possible — there, dew, residual moisture and the deposited straw take over the covering.

Do I need more seed with drone seeding?

Plan for a surcharge of around 10 to 20 percent compared with drilling. In return you save the pass, the soil compaction and the tramlines.

Does drone seeding also work without rain?

The seeding does, the emergence does not. That is why we schedule as close as possible before a forecast period of rainfall — or into the standing crop, where it stays moist underneath.

What does cover crop seeding by drone cost?

That depends on the area, the seed rate, the travel distance and whether you supply the seed yourself. In our order portal you draw your fields and see a no-obligation guide price in about two minutes — before you even send an enquiry.

And if things get tight again this year?

Then call us before the combine runs — not after. Pre-harvest seeding is the only method that gives you real growing season back, and it has a window of a few weeks. Everything else about the process, the seed and the documentation is on our service page Seeding cover crops by drone. If you are more concerned with green cover in standing maize or cereals: Undersowing by drone. If your problem right now is the soil rather than the calendar: Seeding in wet conditions — what to do when the field will not carry. And if the question of price comes with it: Drone seeding — costs and economics honestly calculated.