Basic guidelines for soil preparation and onion sowing

Tillage  and sowing

Sowing onions is a precise job because the seeds are fine and should not be sown too deep. We recommend sowing 1.5 to 2.5 cm deep on a firm moist soil. Before sowing, you first have to till the soil, of course. On sand, this means ploughing, digging and in some cases non-turning tillage. In all cases, ensure a flat seedbed.  The following applies to each type of tillage: make sure the soil does not dry out too deeply. We are dealing with drying weather, which means the top layer of the ploughed soil can dry out too much. After ploughing or spading, the soil must be “closed”. This means that when ploughing the soil, the seedbed is prepared immediately, so only the top layer dries but the seedbed remains sufficiently moist. If you use a furrow packer, we recommend combining this with a “follower” (a cross roller, or a Cambridge roller ,etc.). This way, the soil is also “closed” and the moisture remains at the top. This also applies to the aforementioned  tillages. Till the soil shortly before sowing.

When you start sowing, check at what depth the soil is moist and adjust the sowing depth accordingly. When sowing, check regularly whether the seeds are well pressed into the moist soil. Repeat this several times.

Plant numbers

Depending on the bed width and the number of rows, the seed is distributed. Regardless of the sowing system, the most ideal plant number is between 80-90 pl./m2. Plant number generally means a good yield, especially when varieties are used that have a relatively high specific weight, which means they are already heavy in themselves. The number of plants per linear metre is shown on the right, depending on the width of the bed and the number of rows per bed.

Thousand grain weight

The thousand grain weight of onion seed is always stated on the bags and can vary quite a bit. The risk is that too much or too little seed is sown, which can cause an irregular crop position.

When the seed drill is adjusted to a thousand grain weight of 4.2 grams and a following variety has a thousand grain weight of, for example, 3.6 grams, this can cause double seeds on the sowing discs if the suction pressure of the seeder is not adjusted accordingly, and therefore an irregularity in the position of the crop. So check this carefully!

Mineral administration

What the plant needs in terms of minerals to achieve its kilos, but also to continue to meet the right quality requirements is very important. When which mineral is needed and at which growth stage the plant has the greatest need for the elements is crucial for the quality and final yield. Talk to your fertiliser supplier/business consultant and ask what would be wise for each type of soil and variety. For example, if you grow onions on light sandy soil, this requires a different strategy in terms of mineral application than if you have onions on clay soil of 40% silt.