[andtiggertoo]

I have picked up a box of organic root veg and onion fertiliser when i bought my seed spuds. It is a granular fertiliser which looks like very small grey pebbles, part of the 'growing success' range

I am growing in raised beds in rotation and have been putting as much home made compost in as possible, this year will be the fourth year. My basic soil type is clay, but the beds have had a lot of compost on now so are quite nice and loamy.

Last year's spuds were a bit poor so I thought adding some fertiliser might be good this year. The NPK ratio is 6-6-12, but the box doesn't specify how much to use just 'lightly sprinkle'. One person's lightly sprinkle could be very different to another's 

In the past i have used pelleted chicken manure. I was going to put the fertilser on the potato bed and the onion bed. What rate would you recommend and how much digging in do I need. The potato bed currently has a 4" layer of quite fibrous compost on that I am hoping the worms will help pull under, but I will do a bit of this as I plant the spuds in a few weeks time.

Thanks

[Trillium]

Normally it would say somewhere on the container what the recommended rate is.

Hard to guess as we don't know the concentrations, so check the box sides or back.

[andtiggertoo]

I have scrutinised the box and nowhere does it say what the useage rate is. I have emailed the manufacturers.

However, after rootling around in the cellar I have found a very old box of potato fertiliser which says 4oz per square yard. This also confirms what I have also found in an RHS veg book for potatoes. For onions the rate is 2 to 3 oz per square yard.

[Kristen]

after rootling around in the cellar I have found a very old box of potato fertiliser which says 4oz per square yard.

I reckon that's fine provided the NPK of your new fertilizer is the same/similar.

i.e. if you have some 20:20:20 then you only need half as much to get the same effect as using some 10:10:10

[andtiggertoo]

OK thanks, I will check the ratios on both boxes. Will also wait for the email response.

I think it is an oversight on the part of the box designer of the new product, there is an enormous amount of info about spacing the veg but nothing on usage of product per meter.

[Kristen]

Dunno if it helps, or is similar, but I got Vitax Organic Potato Fertilizer when I bought my Spuds (from JBA)

That says:

NPK (UK version) = 4 : 2.5 : 8

4oz per sq. yard

Potato Barrels / Planters: 12" pot = 10g, 25" pot = 15g, 20" pot = 30g

[andtiggertoo]

thanks Kristen

[Trillium]

Guess whoever designed the box forgot a bit of common sense 

[Trikidiki]

There are too many variables to be too precise.

If you have grown potatoes on the plot the year before it is going to be quite depleted, whereas if you have grown beans or other legumes then you won't need a huge amount of Nitrogen early on.

If your soil is clay then you won't need as much fertiliser as you would on a sandy soil where the nutrients wil have been leached by winter rain. High organic matter will hold onto nutrients well over winter as well.

A recent application of not-well rotted organic matter will deplete the soil of nitrogen.

Adding too much fertiliser can cause problems as well. Too much potash may inhibit the uptake of magnesium.

Go with the light sprinkle, you won't be too far out.

[andtiggertoo]

Thanks Trikidiki. This is a helpful list of variables that can impact on the fertility of the soil.

I grew onions in that bed last year, the soil is rich in organic matter which is quite well rotted down and I have not put any other fertiliser on for at least a year.

Today was my only day off so I got on with applying the fertiliser. No response from the manufacturers yet. I applied at a rate of 4 oz per meter square. The spuds won't be going in for another 8 weeks so the granules will have had chance to break down and work down into the depths of the bed.

Will just have to see what happens, but thanks for advice.

[Trikidiki]

If you have plenty of organic matter you are likely to be ok for Phosphate and Potash. Keep an eye on the leaves and if they start to look yellow then give them another sprinkling with a general purpose fertiliser.

If you can get some put some manure in the trench or planting hole with each potato, failing that some grass clippings under the seed potato will help. Both will add a little fertiliser but also keep it fairly acid and help prevent scab.

[Salmo]

Many boxes of fertiliser or grass seed give instructions, for instance, 4 oz per square yard. The problem is always that you have no idea what 4 oz looks like.

Weigh 4 oz out at home on the kitchen scales and tip it into your hand. Then remember what it looks like.