WHEN the smoke clears after this weekends fireworks spectaculars and bonfire celebrations, all that will be left will be smoldering heaps of ash and embers. Gardeners should take a closer look at those grey piles though, as wood ash has been a traditional soil improver for centuries.

There are certainly beneficial plant nutrients to be had from this plentiful post November 5 resource, but a little care should be taken over their provenance. If treated or painted timber, chipboard, rubber, plastics, old sofas and the like have been part of the make-up, then the fire site is best left alone. If, on the other hand, only clean and natural tree branches and timber have gone into the mix, then when the resulting fire has had time to cool off, it is time to return what remains to the soil.

Wood ash contains relatively high levels of the essential plant nutrients potassium, known as ‘potash’ to gardeners, and smaller amounts of phosphorous. The potash in particular is needed to encourage healthy flowering and particularly fruiting. Traditionally the ashes were sprinkled around gooseberry and redcurrant bushes to promote bigger healthier crops. This must be done fairly promptly however as the nutrients are soon washed out and into the soil by rain. They are also a lot easier to sprinkle when dry, rather than when wetted to a sticky, sloppy grey mud.

A word of warning here however. These ashes are also significantly limy. They have high levels of calcium and can rapidly raise the pH of the soil. No problem in small amounts around plants that will not object, but best avoided around lovers of really acid conditions, like blueberries or rhododendrons for instance.

Perhaps the best way to recycle the nutrients contained in wood ashes is to use them on the compost heap. Not all at once, but a sprinkled shovelful now and again. Here, the lime content is particularly beneficial in counteracting the tendency for the composting of kitchen and garden waste to produce an acidic mixture. Brandlings, those small red worms so welcomed by composting experts will thrive as the pH rises.

Regular fires in the garden may be a thing of the past - unpopular with neighbours and redundant through home and council green waste collection schemes. But at least once a year, thanks to Guy Fawkes, there is an opportunity to collect useful wood ashes - grey garden gold!

Chris Crowder is head gardener at Levens Hall

chris.crowder@me.com

Jobs to do this week:

This weekend is a good time to gather up all your woody waste material and prunings and burn them. Even if you are not having a fire, someone nearby will be and will welcome your contribution.

Cut back and tidy up herbaceous plantings if they are not needed to provide winter interest.

This is the best time to plant tulips for a spectacular display in spring.