I am planting shrubs in borders in a field that has been meadow since the Domesday Book except for a few years when it was used for pig /sheep grazing. A local farmer (forced to farm on Essex clay! - yuk) was saying what wonderful soil I had???? He said we had vetch (I think) which means the soil is acid ( in Essex!!!). The problem I have is that despite digging in the ash from my woodburner & chucking around potassium sulphate - flower/fruit production is awful - if at all. Soooooo I have bought some more - any idea as to how much & when. I have done a soil test - the soil is high in phosphorus & depleted nitrogen & potassium.
The actual meadow grass containing the vetch has been there for several hundred years. The matted "grass" roots extend down about 7 inches below the meadow & are fairly impenetrable. Maybe the nutrients just never get past it. Also the village I live in was built on the site of an old glacier - several feet under my clay soil is gravel - therefore my clay soil drains well!!!!!!!
Trees are grow well despite the lack of nitrogen - probably bacause of the phosphorous.
Was v lucky this winter when the UK had lots & lots & lots of heavy rain. There was flooding over most areas but not in this village!!! Downside is we are not far from the driest place in England so we usually end up with drought conditions in summer. Nice today tho' 75 degrees
Your vetch/grass root structure is a great resource, adding lots of organic material in place. Some nitrogen is used up when it rots but eventually some is returned for your plant roots. If you haven't got a compost pile going, you should try for one. Clay soils do better when they are well mulched so the surfaces don't alternately bake and then get pulverized by raindrops.
Sounds like you might have glacier clay which is tight but not to bad if you keep enough organic content. So watch out you don't put too much nitrogen into the soil or you might accelerate decomposition. Also wood ashes are very alkaline and high in potash -- odd that you soil tests low in potassium -- should be able to add more ash and also help get the pH up toward neutral of 7.0.
You might also try folier feeding a soluable kelp product. I don't know what you have in the UK but I use Maxi-Crop with good success. The kelp has nitrogen (along with lots of other nutrients) and will get foliage and flowers going. This goes straight to the plant and will not have much effect on the soil BTW. Use a watering can or better a pump sporayer (the 2 litre pressurized kind, not a hand held, unless you like pain and cramps in your hand)
Epsom salts are a good quick source of potassium-add a few tablespoons per square meter of clay
Since I first posted I've been digging in old compost , & sprinkling Growmore & potassium suphate around ( then hoeing it in) I've been watering my plants with a soluble fertiliser mixed with seaweed extract. Plants look healthy - hope I get some flowers next year!
Check with your county coop extension; they probably have soil surveys & I find them to be very accurate here. Sometimes you have to literally BUILD your soil to get the tilth and organic content you want, but it's worth any amount of work & time it takes over the long haul. Start composting if you haven't yet. NO gardener I ever met complained that they ever wished they HAD'NT double-dug their beds & worked in all that good compost; everyone always wishes they'd done even more. I spend a LOT of time now on the soil of every new bed I prepare: (a telephone pole would sprout leaves in my beds now) & it saves me a TON of work by giving me such strong disease-resistant plants that it was worth all the sweat & effort.
Thanks for that Lindap. I think you're right. Nows a good time to make a start ( except I'm not in the UK at the minute...I'm taking in the sun for the next seven weeks in Naples Fl!)I'll make a start when I get back by digging to enable any frost to break up the clay