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Giant Sunflowers using biochar super compost

Tony Callaghan 29/09/2016

Giant Sunflowers using biochar super compost

Giant sunflowers are grown using biochar super compost 

We planted our sunflowers (Russian Giant) into the test beds very late this year, in early August, after the Charlotte potatoes came out. The thinking was simple; sunflowers need lots of water and nutrients and they will really test the different soil additive mixes. 

If you have followed the earlier posts on potatoes and radishes, then you know we have five soil test beds. 

One clayey soil (control), clay plus our super soil additive (code named SF60), clay soil plus compost from our HOTBIN®  (i.e. high colloidal humus compost), clay soil plus raw biochar, clay soil plus ‘shop’ bought compost.

The SF60 Biochar Super Compost (Soil Improver) formulation has resulted in 2.7m high Sunflowers and the earliest flower heads. They are 32% taller than the average.  

The sunflowers grown with soil plus 'raw biochar' were 1.6m height. Those using compost from our HOTBIN® and shop compost were equal at 1.8 and 1.9m. The control is interesting; it is currently 2.2m – but!

The clay control sunflower has a fascinating story. A few weeks back, I noticed the soil height in all the tests beds had dropped some 10cm below the top rail. Basically the soil had compressed since filling for the first time back in September last year. The decision was taken to top-up at end of the season with like-for-like mixes. Then my neighbour tore up a path of garden to make a new patio and offered me one tonne of soil. 

I wheelbarrowed it all back. I was running out of a space to store it. I thought well it’s same clay soil as the control – it won’t affect things if I add the extra soil in to one bin now. How wrong was that! 

At the time of addition (four weeks ago) the clay soil sunflowers were second to last place. 

But four weeks later, one week of heavy rain and two weeks of fantastic late summer sunshine and bang – they caught up the best performer. I’m pretty sure this is all down to water. The extra clay not only holds water; it has stopped the layer below drying out as fast – they had more water than other tests beds.

So this brings us back to the test.

The sunflowers tests indicate water retention within the soil additive as one of the most critical features, especially when looking at flowers in the late summer months. 

Those who have read up on biochar as a soil additive will be asking – but surely biochar holds water. Why did the Sunflowers in biochar do poorly? Surely compost also holds water? 

All these are true – the key question is “how much water (holding capacity) and, in terms of the biochar article, how long for (water retention time)”.


Why Does Biochar Super Compost work?

Consider this table of soil raw material properties:

Compost and biochar improve poor soils. Colloidal humus retains a lot more water. Just as importantly it holds onto to it for far longer. Compost dries at 100C in about two hours. A similar size colloidal humus sample would only be dry after 8-10 hours – it just doesn’t let go! 

Not sure? You can try for yourself by taking 100g samples of BBQ charcoal, compost, clay soil. Wet them, roll into a ball in palm and leave them out in sun. Every hour check to see if they fall apart or are still pliable. The alternative is to use the kitchen oven to dry – but best check first. We might know all germs are killed within minutes at 100C, it still doesn’t mean the cook will be happy.

Colloidal humus is remarkable stuff. Even small amounts have a profound impact on soil. So why not just add loads of colloidal humus to the soil. Well, you need balance. Pure Humus is a sticky mass full of water. It does not let the soil breath (roots need oxygen). In essence, the soil needs more colloidal humus, but not too much! 

What we are attempting to create with SF60 is the world’s best, (completely natural and sustainable) soil additive. OK we know that’s a huge goal for a small team, but we are very close. Want to test for yourself? Buy SF60 here!

PS: want to know how not to grow tall sunflowers? Plant seeds direct into poor clay soil, next to shed (shaded for part day and protected from rainfall. Leave them to fend for themselves and compete with weeds. Do not provide extra water. The seeds we planted have been in twice as long as those in test beds (16 weeks versus eight weeks). They are pathetic weaklings at 0.3m height and no signs of flowers. That’s a huge eight fold smaller. Nature has such huge capacity to change plant growth!