Because of an increase in extreme weather events and rising fertiliser prices, the cultivation of catch crops becomes increasingly important. The focus is primarily on the positive effects on the soil. Among other things, catch crops protect the soil surface from erosion, improve soil structure and encourage the biological activity of the soil. At the same time, they ensure deep root penetration and fix nutrients.
However, in many regions, the current weather conditions pose a challenge to catch crop cultivation. The UFZ Drought Monitor for Germany indicates a severe drought in the summer of 2026 with significant regional variations; drought intensity in the soil as a whole, down to a depth of two metres, is considerably higher than in the topsoil. This is due to an excessively dry spring and high evaporation rates.
This raises the question of the correct time to sow catch crops to ensure it becomes well-established.
In general, the optimal seed time depends on several factors, such as the type of catch crop or the specific site conditions.
A rule of thumb illustrates the importance of early seeding: one day’s growth in July is roughly equivalent to one week in August and one month in September (Chamber of Agriculture North Rhine-Westphalia).
This statement gives the impression that the earlier, the better. The light and temperature conditions of midsummer can be optimally used to make sure that the catch crop becomes establishe rapidly, covers the soil quickly, develops an extensive root system and produces a large amount of biomass.
However, an early seed date alone does not guarantee success. It is crucial that the catch crop is able to germinate and establish itself reliably in the prevailing conditions.
This can be particularly challenging in dry years. If the soil is severely dried out after harvest and there is a lack of soil moisture, the seeds often germinate only slowly or unevenly. Therefore, the focus is even more strongly on optimal seed placement and proper seed-soil contact. In extreme cases of prolonged drought, germination may even fail completely.
If emergence is successful despite the dry conditions – even with a delay or unevenly – an initially weak population does not necessarily mean failure. The crucial factor is that the plants are able to establish themselves and develop a root system.
While in favourable conditions a great deal of energy is channelled into leaf mass and biomass formation, established plants invest more intensively in their root system in case of drought stress. They develop longer taproots and more fine roots to access water and nutrient reserves from deeper soil layers.
A glance at the surface can therefore be misleading: even a sparse population can already trigger important processes in the soil. The roots loosen the soil, encourage the biological activity of the soil and lay the foundation for humus formation and a stable soil structure.
Early seeding generally offers the greatest potential for biomass production and root development. Even if the crop initially shows little above-ground growth during dry periods, the catch crop can already be doing valuable work underground.
However, this depends on the reliable germination of the seeds. If the necessary soil moisture is lacking after harvest, the seeds may germinate unevenly or, in the worst case, lose their viability. In this case, the positive effects of root development will also fail to appear.
Therefore, in some cases, it may make sense to deliberately postpone the seed date.
The key factor is not only the earliest possible date, but a rather reliable and even emergence. A dense population that establishes itself after an appropriate precipitation event can often fulfil its functions more effectively than a catch crop sown too early but with gaps.
When sowing later, the choice of species has to be adapted to the shorter development period. Fast-establishing species such as mustard, oil radish or phacelia can still deliver good results even at the end of August. Heat-loving legumes, on the other hand, benefit more from early seed dates, as they require a longer vegetation period for their development.
