What is the best fertilizer or fertiliser for Potatoes ?

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After last years experiment with growing potatoes in tubs ready for Christmas days dinner. I thought I had better look into the reasons behind the failure. Or apparent failure. They produced too many green leaves and to few potatoes in quantity and size.

Last year I did use a compound fertilizer called triple 14 or 14-14-14 which has an equal percentage of NPK, that is Nitrogen, phosphate, and potassium. With an application on intial planting of first layer, followed by another application on the final 3rd layer.

This was a pelletized or granular fertilizer which makes using very easy, and is slow release, of about 2 to 3 months. My failure there as the potatoes were only in the tubs for a very short time, so I had given them double the amount of Nitrogen.

So whats on the market. I searched via Google and came up with following 19 brands. These are random brands thrown up by Google, I have no affiliation with any of these. The data is as stated on each applicable search results website. All the results were pellitized fertilizers apart from one which is liquid. You will also see that a few have identical chemical mixes, and my thoughts are that they mass produced and reboxed/rebagged under a a 3rd party brand.

Please be aware that something like 15:9:20 denotes the chemical breakdown, and it refers to N – Nitrogen, P – Phosphorus, K – Potash (Potassium) or NPK as its known. The chemicals used can be a mix of N = Ammonium Nitrate, P = Phosphate (Rock phosphate), K = Potash (Rock deposits) and Sulphur/Sulfur = Ammonium Sulphate. There are lots of other chemicals that can be used.

Fertilizer comes as a Compound mix of the 3 elements. Each element can be bought seperatley and are known as a Straights’.

Blended Base Fertiliser ProGrower Potato Fertiliser – 15:9:20 + (Trace Elements + 9.5%So3 + 1.8%MgO)

Chicken manure pellets – 4.5:3.5:2.5 + trace elements

Comfrey leaves/liquid –  1.80:0.50:5.30 + trace elements

Vitax Organic Potato fertiliser – 4:2.5:8

Potato And Vegetable Fertiliser Professional Grade – 8:24:24+5%SO3

POTATO FERTILISER DRY GRANULAR – 13:13:20

Thomas Elliott Potato Fertilizers – 6:10:10

Pleveys (Thomas Elliott Potato Fertilizers) – 13:13:20

Kings Seeds Potato Fertiliser – 14:14:21

SimplySeeds – 6:10:10

angus-horticulture – Potato Fertiliser – 14:13:21

Just Grow – BOLD Potato Fertiliser – 7:14:20

Jamieson Brothers® Granular Potato Fertiliser – 13:13:20

Johnston Supplies – 8:24:24 + 5% SO3 Sulphur

Spear and Jackson – Organic Potato Feed – 1,5L LIQUID– 2.2:1:3.4

Horticare POTATO FERTILISER – no formulation found

Potato Fertiliser – 14:14:21 with Magnesium, Boron and other trace elements

Chempak® Potato Fertiliser – 4:6:12 +4MgO

Westland 1.5kg Organic Potato – 4:2:10

Organic Base Potatoe Fertiliser – 12:6:6

YaraMila ACTYVA S – 15.6:14.6:14.6 + 6.5% SO3 (used at planting)

YaraVita MAGPHOS K – 0:19.2:6.2 +6MgO (used at start of tuber growth)

You will see that some fertilizers also have something like +5%SO3 at the end of the NPK figure. This denotes the amount of Sulphur that has been added.

Also some say “+trace elements” or “micronutrients” or with “Magnesium, Boron” or even “+1.8%MgO”. These are trace elements essential for the healthy growth of the plant and also to assist in the take up of the NPK chemicals.

The actual amount of all chemicals NPK and trace elements required by the plant changes throughout the year. With potatoes this split into 6 periods for the farmer, or maybe just 2 for the home gardener.

The periods being

1 – At planting

2 – Tuber growing and bulking

The following has been taken directly from https://www.yara.co.uk These are the professional suppliers of fertilizer for farmers. This gives an excellent breakdown and a good understanding as to what the elements are used for. I believe most home gardeners would just go with “Planting” and “Flowering and bulking”.

Planting :
Nitrogen and Potassium – early growth and dry matter
Phosphate – more tubers, growth and dry matter
Magnesium – for plant development
Zinc and Manganese – Powdery and Common Scab control
Sulphur – Common and Powdery Scab and tuber numbers

Before tuber initiation (Hook stage) :
Phosphate – more tubers, stronger growth

Tuber initiation :
Phosphate and Magnesium – bigger tubers
Zinc and Manganese – skin finish
Calcium (+/- Boron) – good skin quality, internal rust spot reduction, stress tolerance – drought/heat

Flowering and bulking :
Nitrogen, Phosphate and Magnesium – maintain tuber growth
Calcium – improves skin finish and reduces disease impact

For additional info please checkout https://www.yara.co.uk/crop-nutrition/potato/potato-nutritional-summary/

Also for nutrient deficiency, identify and diagnose have a check at the bottom of this page  https://www.yara.co.uk/crop-nutrition/potato/

For more interesting fertilizer reading I would refer you to https://www.diamondfertilisers.co.uk/products/

Therefore my targets for this year are for the first 1 month using “triple 14” or 14-14-14 purely for leaf growth, then the remaining growing period 8:24:24+5%SO3 which has a lower Nitrogen content and an increase in potassium and Sulphur. This should reduce the amount of top growth, but provides for tuber growth and reduce scab.

Additional potash will be beneficial. This can be gained by applying 250 grams of wood ash per square metre. Make sure only wood ash and no plastic contamination.

Soil pH levels between 5.5 and 7.0 are cond90ucive to the development of scab, recommendation for potatoes in acidic soil of 5.0 pH

Disclaimer – These are my own personal thoughts and understanding. Always read the product label and safety labels,