Our agronomist, Mike Wainwright, on how nutrition requirements for crops shift over the winter months:
"We all notice the changing of the seasons in different ways. For some of us it’s having to use headlights when we drive to work, for others its putting a hoody on as well as a tee-shirt, but sure enough, little by little, the seasons are turning.
Plants also respond to the changing weather and light conditions in various ways. There is no single trigger that switches a plant into ‘time to prepare for winter’ mode, but the shortening day length and cooler conditions reduce the rate of activity of many biological functions impacting on plant growth and vigour.
Glasshouse crops may be protected from the winter cold to a greater or lesser extent, but unless crops also have the benefit of supplementary lighting, the short days and low light levels will naturally result in much reduced growth rates compared to the summer months.
Decisions on autumn and winter feeding of crops have to take all these factors into account, and a lot more besides. There’s no point in producing a flush of vibrant green growth in November on plants that aren’t going to be sold until the spring. Conversely a seasonal crop such as Poinsettias will be actively growing throughout the autumn period when many other crops are slowing down, so the feeding regime needs to supply a very different nutrient balance to reflect this.
Hence taking account of the crop cycle and environmental conditions the crop is grown under is vital in determining correct fertiliser selection and application rate throughout each phase of the year. Many growers find that a fertiliser ratio of 2:1:4 (N:P:K) during the autumn and winter is ideal in providing enough nitrogen for sturdy resilient growth, whilst not encouraging lush or weak growth that would be prone to infection by Botrytis or other fungal diseases. In general, reducing the nitrogen provision during the autumn and winter, whilst also increasing the potassium ratio will give many protected crops the best combination to encourage healthy growth. HortiMix 15-7-30+1.6MgO+TE soluble fertiliser is widely used for this purpose, also having a generous trace element package to ensure crops have the full range of nutrients needed to support and sustain growth.
Increasing the supply of potassium during the autumn and winter has a significant benefit in hardening crops and increasing resistance to environmental stresses such as cold and frost. Potassium has a vital role in water regulation within plant cells and the movement of sugars from where they are produced to where they are needed. Having the correct levels of both sugars and potassium acts like an antifreeze in maximising the cells ability to withstand chill injury.
Where crops just need to be held over winter prior to spring sale or potting with minimal growth requirement, I recommend HortiMix 12-6-36+2.5MgO+TE soluble fertiliser, having an even higher potassium to nitrogen ratio.
For autumn and winter flowering crops of primulas and pansies for example, Hortifeeds has the bespoke HortiMix Primula and Pansy Special, which has enhanced levels of magnesium, and generous levels of iron chelated by DTPA to improve uptake even when growing media pH is elevated. Other crop specific soluble mixes are available to suit individual crop requirements, just contact your Sales Manager for more information.
While getting the balance for autumn and winter feeding is important, just ensure you plan ahead beyond this colder weather and give your crops the best start to spring!"