December 2008


Updates from December 2008.

Food gardens in December.

15December in the northern hemisphere is often seen as a time to bring out the spade and ‘turn over’ or ‘break up’ the soil. I know quite a few people who actually enjoy doing this, as well as liking the sight of bare, lumpy earth, and I have no wish to deprive them of this pleasure. But for the rest of us, how necessary is it?

Many gardeners have been taught by respectable bodies such as the RHS that autumn digging is vital for next year’s growth. They read frequent pieces of advice in the gardening media about the need to dig and aerate their soil, and to incorporate manures and compost. This advice has become deeply held belief and is now incorporated two spits deep in peoples’ brains!

So please allow me to help dissolve it, if digging the soil is a job that you would rather not do. Instead, you could be sourcing or making compost and manure to spread on top of the soil, for worms to come up and find, repeatedly. In so doing, they aerate your soil. It is as simple as that. What is more, their aeration is more permanent and stable than when soil is broken forcibly by tools, rotovation included. Worms create air and drainage channels that endure – just look at how grass keeps growing on sports pitches, despite being pounded week after wet week.

If a football match were to take place on dug ground, where the lattice work has been broken, it would soon be trench warfare. I know that grass roots make a difference too, but soil structure and its associated life are key aspects that we ignore at our peril, or encourage to our benefit. Soil life is not encouraged by being turned upside down and broken into fragments.

Regular readers of mine will perhaps be tired of me repeating this, if so I apologise, but the habit of digging and rotavating is so accepted, even in our language, that I feel bound to keep ploughing the same furrow! Let’s just look at some results from my experiment of four beds 1.5×2.5 metres.

Two of the beds were first dug in March 2007, with compost and manure incorporated underneath a spit of grass turf, which was placed upside down above the organic matter. The other two beds were not dug or touched in any way except to place the same amount of organic matter on top of the pasture turf. I spread 5cm (2”) of well rotted horse manure and 10cm (4”) of green waste compost, which was sufficient to kill grass, buttercups and even dandelions. The same amount of manure and compost in the dug beds meant that all four beds were at least 15cm (6”) above soil level, with boards of wood around them and paths of 45cm (18”) in between. See photo.

The soil is a heavy clay loam which comes up in intractable lumps when dug, needing either frost or alternate drying and wetting before a tilth is possible. On the undug beds, sowing and planting is straight into the compost on top.

I work the beds in two pairs of dug and not dug, growing the same vegetables in each pair. Most are from plants raised in the greenhouse, enabling rapid establishment of both spring crops and then second crops in late summer. Looking through the table below should give you an idea of the cropping plan. In 2007, because the beds were only made in March, beds 3 and 4 were partly single-cropped only, with slightly later plantings. Some of this is apparent in the photos, beds 1 and 2 are nearest to camera, in May then in early September

Harvests Dig/No Dig by Charles Dowding, 2007
BEDS 1 & 2
  Dug Not dug  
Lettuce leaves 5850 6650 18 plants each bed, 3 months picking
Beetroot 3050 3290  
Chard 3825 5095  
Calabrese 1120 620 some cabbage root fly damage
Onions 3540 3450 bad mildew on all onions lowered yields
1st harvests total 17385 19105 (more leaves mostly)  
SECOND HARVESTS, BEDS 1 & 2
  Dug Not dug  
Leaf radish 350 350 cabbage root fly damage
Lettuce, leaf 1890 2700  
Turnip 3100 2600 roots of tennis ball size on average
Swedes 4770 (4 roots) 320 (1 root) gall midge damage on no dig
Sugarloaf chicory 2620 3870  
2nd Harvests total 12730 9840  
Grand total 30115 (30.12kg) 28945 (28.95kg)  
BEDS 3 & 4 (planted later than 1&2)
  DUG UNDUG  
Lettuce hearts 280 330  
Dwarf beans 500 1325 slug damage to plants on dug bed
Spring onions 1250 1310  
Show onions 3670 3430 5 onions both beds
Carrots 3100 7980 less slug damage to seedlings, undug beds
Red cabbage 3550 2930  
Celeriac 2240 (4, one tiny) 3730 (5)  
Leeks 1360 1510 leeks were longer on undug bed
Mustards 980 930  
Chicories 1620 2160  
Grand total 18550 (18.55kg) 25635 (25.64kg)  

 TOTALS OF THE FOUR BEDS:

Two dug beds – 48.67kg
Two undug beds – 54.59kg

NOTE that weights recorded are of the plants’ main edible parts only, e.g. cabbage outer leaves discarded, onions and celeriac trimmed, beetroot leaves removed etc.

Characteristics of growth differences.

The undug beds showed quicker growth in spring for almost all crops, while the dug beds caught up in summer and autumn for most crops. Salad leaves were nearly all more productive and suffering a little less slug damaged on the undug beds, while the brassicas tended to do better on dug beds.
It will be interesting to set these results against those of 2008. See my January blog when all harvests are in.

Charles Dowding.