Tuesday, 13 March 2012

Liming the brassica bed

Following the instructions very carefully, I have found that the new brassica bed has a pH of about 7 and the new onion bed has a pH of 6.5.  This surprised me because of the amount of organic matter I have been adding to the soil.  Also I have been using the X Cupressocyparis leylandii shredded leaves and branches to add to the subsoil. There seems to be some thought that this would make the soil particularly acidic.  It does not seem to be having any effect on  the pH of my top soil.   I purposely took samples from the beds with the largest amount of leylandii on them.  So, is this another myth busted?

Using the leylandii and other woody material when triple or "bastard" digging 600mm in depth seems to have some good effects.  Some due to the addition of woody material and others because of the digging.

  • It improves the drainage whilst allowing some water retention.  Thus plants with deep roots can access a reservoir of damp decomposing vegetation during the driest months of the year.  
  • The woody material does not decompose very quickly making it a long lasting method of water retention in the soil. Some of which can reach medium rooted plants by capillary action.  
  • There is a large amount of vegetation slowly decomposing and giving off a certain amount of heat.  This forms a hot bed warming the soil and encouraging root growth.   
  • Triple digging breaks up the subsoil and any iron pan that restricts plant roots.  This will also improve the drainage of the allotment.  
  • The addition of organic matter to the subsoil slowly changes the subsoil to a more top soil consistency.  
  • With the addition of other organic matter such as leaves, weed turf and lawn turf, nutrients from their decomposition can be worked into the sub and top soil after a year or two.
  • Any nitrogen depletion brought about by decomposition of the woody material may be using that leached from the top soil.  This nitrogen will be captured by micro organisms and fixed until they themselves die and add them to the soil through their cells being decomposed.
  • It prevents the woody material being burnt and releasing the locked up nutrients into the air as gaseous oxides.  
  • It helps to sequester a small amount of carbon in the soil. A long journey starts with a small step.   
 The only disadvantage is that you have to dig deep trenches.  However, Hugelkultur suggest that you do not have to bury the woody material.  Hugelkultur involves laying woody material on the surface and covering with topsoil.  I would rather use the trench method.  This is what the indigenous Central and South American  civilizations did in the past  and I have a great admiration for the great horticultural knowledge of these ancient peoples.

Do I lime the brassica bed or not?  I had already bought the lime so I thought that I would still add some lime to maintain the high pH and ward off the dreaded club root Plasmodiophora brassicae.  Also do I lime before or after watering on anti slug nematodes?

Before making these decisions the green manure and weeds needed to be dug into the topsoil.  The soil on this top allotment is very friable because it has been worked for a great number of years.  It did not take me long to dig over all the green manure areas.

The strawberry bed was weeded.  The only weed was the poached egg plant that had seeded two years ago when I used it as a companion plant for the sweet peas.  I would have kept some of the plants but they are more yellow than poached.  They went into the worm bin.

As I needed the ground to be moist and it was a fairly warm day drying out the soil, I watered the ground with very dilute comfrey liquid manure before watering on the nematodes Phasmarhabditis hermaphrodita.  This was a process made much easier by the water being turned on again.  I am hoping that the liquid manure will act as a base dressing and not be leached out before the plants can make use of it.

I limed both the brassica and the onion bed.

The Rheum raponticum var. "Timperley Early" was planted next to the var. "Champagne" in the rhubarb bed.  I thought that I had lost it but it was throwing up some small leaves.  I planted it with a little mychorrhizal fungi and watered it in with dilute comfrey liquid .

The scraps of manure that were left were put around the rhubarb and along the raspberry canes as a mulch.

Things to do tomorrow.

  1. Remember to take an AA battery for the clock.
  2. Get some more straw for the strawberry bed.  I doubt if it will make a bit of difference to the crop but it does look good.  
  3. Put in the posts to support the sweet pea canes and then put up the canes.
  4. Plant the sweet peas, parsnips, carrots and hamburg parsley.  Cover the carrots with a fine mesh barrier to combat Psila rosea. 
  5. Cover the garlic and the shallots with a fine mesh barrier.  By all accounts the Phytomyza gymnostoma begins to hatch out around the 15th to the 18th of March.  The barrier will go over the onions too.  
  6. Cut supports for the fine mesh from the blue, plastic water pipe.  
  7. Crop the purple sprouting broccoli.
  8. Put new roofing felt on the two sheds then paint with preservative.   


  1. Conifer needles produce a lot of humic acid as they rot, unlike deciduous leaves. I'm not sure about the wood. Any effect on pH obviously depends on the quantity. The soil under coniferous trees soon turns very acid, loses much of its soil fauna as a consequence, and undergoes structural changes because there are no worms to turn it over. If you put it all two feet down, it won't affect the topsoil at all.

  2. This is what I found Robert. The acidity of conifers does not seem to affect the top soil when buried at least 2 feet below the surface.