Brussels Sprouts - super compost and biochar test results - just in time for Christmas lunch!

Followers on from our blog on testing compost, super compost, colloidal humus and biochar amended soils in raised beds we know we have been achieving some great results (sunflowers, potatoes, radish).

After a full season of testing, our final crop (Brussels sprouts) have just be taken out ready for Christmas day. The results are surprising!

The highlight: adding SF60 Super Compost (i.e. a formulation of colloidal humus - biochar-organic matter gave a 19% crop increase.  Adding standard compost and raw biochar had a negative impact - but the important thing we need to know is why!

Tabulated Test Results

Note: * In experiments you are not supposed to change things! In September, we were bringing in some top soil ready to refill the raised beds at the end of growing season. (All the beds had sunk as the soil settled). We were short of storage space and thought - it won't make a difference if we add 10 cm of clay on top of the clay only bed. Well it did! We saw a massive growth spurt in both the sunflowers and the Brussels sprouts. Within a period of a month, from being 'behind' and smaller in the clay bed, they were visibly ahead in leaf span and plant height. This gain has carried through to the final results. The actual weights for the control were 2800g and 1200g. The table values listed have been factored back to where we honestly believe they were would have been without the extra clay soil. We are aware earthing-up potatoes, but not heard about impact on sprouts before. Let us know your experiences!

General Observations:

The sprout results are not well aligned with other crop results - why?

We believe all the beds had sufficient nutrients such that lack of nutrients was not limiting growth (see earlier results).

We believe water retention in the test beds had the biggest positive and negative impact on sprout growth. The soils with the best water retention had the best results. The clay soil topped up with water retentive clay created a big growth spurt. The beds which showed poor water retention all year (biochar and standard compost) faired poorly.

Genetics seems to trump amending soil. Where nature has adapted a plant to grow and prosper in heavy clay conditions, amending the soil to be a light tilth does not help!

What would we do next time assuming we were not testing? Add 5-10% by volume of SF60 Super Compost (i.e. a colloidal humus-biochar-organic matter mix) to gain a 20% crop increase.

Learning tips for Brussels sprouts in future:

• Take the crowns out much earlier: e.g. 6 weeks before harvest. (This drives the energy from leaf growth into sprouts. It helps the smaller sprouts near the top plump out).
• Consider 'earthing-up' around the sprout base. (We found the extra 10 cm of top soil added in autumn had a big positive impact)
• Many will know this, but avoid 'light', high tilth soils for sprouts. Avoid soils with lots of compost or biochar - at least during year one after adding!
• Don't wait too long before cutting the sprouts - cut them before they burst. We waited a couple of weeks too long and two of the five stalks had started to flower!