Undercover Job!

Answered by Harrod Horticultural Posted in Category Soil, Feed & Fertilisers

Dear Martin

This is my first attempt at growing veg, and I need all the help I can get. I have just dug up three plots 10x5 ft., the ground was covered with black plastic and gravel over the top, it’s been covered for about 8 years. I have tested the soil and found it to be as follows; the p.h.is 6.0, Nitrogen is low, posphorus is low and  potassium is medium to low.

Please how do I begin to get this put right for this coming year.

Thank you  

Brian Duck

Dear Brian

The situation doesn’t sound too bad; the ph levels are almost where you want them for growing most vegetables and the lack of nitrogen and potassium is only to be expected. Both these situations are relatively simple to rectify, as I shall explain below…  

Most vegetables prefer a soil ph of around 6.5, with the exception of potatoes and rhubarb which enjoy slightly more acid conditions. The ph level of soil can easily be raised by digging in some garden lime (available from all good garden centres) and you can read a lot more on this subject in a previous ‘Ask the Expert’ entry.  

Whether you choose to garden organically or otherwise, there are various fertilisers available which will increase the amount of the three main nutrient elements (N:P:K) present in your soil. Inorganic examples include sulphate of ammonia (for nitrogen), sulphate of potash (for potassium) and triple superphosphate (phosphorous). There is a multitude of other general purpose inorganic fertilisers available – just check the NPK rating on the box to find out exactly what you’re adding to your soil. If you prefer to follow the organic  road, you can boost the nitrogen content of your soil with dried blood; phosphorous can be increased with an application of blood, fish and bone and use wood ashes to improve the potassium level. You’ll find wood ashes will also increase the lime content of your soil and will help raise the ph to 6.5.  

As your plots (as they now are) have remained dormant for so long, the structure of the soil will need improving. This basically means the soil will be able to retain nutrients, air spaces will be created and water will be able to pass freely through the top levels of soil before being held around the root zone. Improving the soil structure is relatively easy and the answer is compost, either from your own heap or by introducing bought and bagged material (such as the Rolawn blends we supply, or good old  farmyard manure). Just make sure that whatever you add to the soil is well rotted. As a guide your soil should consist of 75% soil and 25% organic matter and if I was in your situation, I’d aim for an end result based on these figures.   

Improving the soil structure is something you can do immediately, either by digging in the material (perfect for warming you up on a cold winter’s day!) or by laying the compost on the soil surface and allowing earthworms and frost action to break the matter down. You’ll still need to dig in the remaining material prior to planting however! Adding fertilisers can wait a while until spring (in your case, I’d apply them as a base dressing and dig the fertiliser into the soil to a depth of 10-12cm) and you will probably also need to top dress (add to the surface) as well during the season when planting out crops. Just make sure the fertiliser granules or whatever form you are using does not come into contact with the plant leaves, as this can cause the plants to scorch and die. Liquid fertilisers are particularly useful for feeding crops during the season as the nutrients reach the plants roots faster and can be absorbed more quickly, and there are liquid feeds for specific crops.

I hope this raft of information is of help but if you have any further questions or queries, please don’t hesitate to contact me – and good luck with your vegetables.