Pete Dollimore and Miles Denyer run Hankham Organics, a nursery and box scheme comprising one and a half acres of glass house and two and a half acres of field crops on the south coast, near Eastbourne. Hankham Organics likes to promote diversity, with forty different types of salad among the many crops that feature in their organic vegetable box.
On a blustery Thursday afternoon, Pete managed to spare some time to spread the message about the inputs you can use for an organic glasshouse.
Pete at home in his glasshouse
What challenges have you faced?
We went through a whole raft of problems, in retrospect I think that was because we were starting with non-organic soils. The soil needed to go through a cold turkey phase before the natural fertility could recover. It took a while to work out what the soil really needed, in terms of how we treat it and what fertility inputs can be used to help the soil rather than just feed the crop. Greenhouse soils also have a lot demanded of them, from both an economic, and fertility perspective.
What are the inputs you use on the farm?
Outside, we would only influence nitrogen levels by using compost and legumes such as clover, but in a glasshouse, it is very hard to justify putting so much ground down to nitrogen-fixers. We maintain levels of fertility predominantly by using compost but also two granular, plant based, organic fertilisers containing high N and K. Based on analysis we have also used Kieserite (Mg) and trace elements such as Boron and Manganese.
Why do you use additional fertiliser?
Leafy crops, such as spinach, and brassicas, such as kale, enjoy a high nitrogen environment. Fruiting crops, such as tomato and courgette have a high demand for potassium. However, in a glasshouse system Phosphate tends to build up, for many reasons including irrigation management and the types of crops grown (very few root crops). Instead of relying exclusively on compost and manures, which provide balanced fertility, we adjust the balance to suit the system by using fertilisers that allow you to specifically replace N and K.
If you go to a fertiliser company and ask them for a fertiliser mix for greenhouses they will give you something that is high in potash, high in nitrogen and low in phosphate.
Why are they particularly important in the spring?
Spring is the time you get the highest demand, we’re trying to produce for the hungry gap. It’s a profitable market when outdoor crops are at their lowest and store crops are running out – so we can grow a lot of produce in the glasshouse and sell most of what we grow for a premium price. The soil is coming back to life and the capacity of the microbial population to process the additional nutrients is high. We’re also very busy at that time of year and so it is a lot more efficient to use fertiliser, rather than wheel in barrow-upon-barrow of compost.
What would happen if you took fertiliser out of your system?
I think we could carry on growing effectively – I just think we’d have to work harder to get what we want. I would probably look towards minimising tillage and scaling things down a little. Fertilisers give us a bit of an edge: to intensify the production, maintain the quality and be economically sustainable. The aim is always to close the fertility cycle but there is invariably a gap between what the market demands and what the growing system can support, this is particularly apparent for us in the glasshouse.
How much organically approved fertiliser do you need?
5 to 8 kilos per year, hardly a bucket-full, for a fifty-square metre bed. When precisely targeted at a certain time of year, I feel it’s a small resource that makes a discernable difference to what we can produce.
End of the season harvest
Have you always used fertilisers in this way?
Early on I had this idea that there would be this kind of Eden under the glass. It’s a different one to what I envisaged and I’ve had to accept that if we’re going to produce in a certain way there are compromises to be made. We went through a learning curve and we started to realise how much and what you can grow depends on your soils ability to support that crop. For a while, we struggled to find and make good quality compost and I become quite obsessed with analysis results and soil chemistry. I think my opinion has balanced out, fertilisers are not essential but useful - to make a reasonable living and help your soils in times of high demand. I would certainly warn against using nutrient specific fertilisers without being sure what is required, you can easily do more harm than good - and it’s a waste!
Do you use any other one-off inputs?
We were getting a problem with mottling in the leaves, so we took them to be analysed. We found that the mottled leaves were 40% lower in manganese than the healthy ones. Our soil has certain characteristics that make it occasionally prone to this, so to address it we sourced an organically acceptable form of trace element manganese and added a small amount to our irrigation system. We used it fortnightly for a couple of months and the turnaround in the crop quality quickly became evident. Not only did crops that were showing deficiencies recover, but plants that previously looked ok started to do even better. We don’t need to use this as an ongoing procedure, it was just about tweaking the system.
How do you manage fertility for the rest of the year?
Generally, we limit fertiliser use to the spring. When we hit summer we just use compost as a top dressing at planting time all the way through to the last planting of the year. Crops such as Tomatoes receive lots of compost at planting and as top dressing through the season. We grow sweet clover one summer in 5 and take soil analysis on an annual basis, mainly to keep an eye on Potash levels.
With organic farming, you’re emulating nature, you don’t need to be chucking fertility at the soil like a sponge. Most soils have an inherent fertility; this seems to be largely dependant on the vitality of the microbial communities. To me organic growing is about trying to understand how we can support this and the commitment to evolving a system that does so.
Sometimes though it just needs a little nudge to keep things healthy.
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