Allotment Growing

Potatoes Fertilizer Programme

Fertiliser Requirements

Potatoes are an extremely productive crop and so a greedy crop. Their requirements and an exact feeding regime will depend on the variety grown as well as the amount of nutrients already in the ground for them.

Assumptions Regarding Nutrients Available

The assumption made here is that the soil is in good heart and that a reasonable level of NPK is there to start. If breaking new ground, or exhausted ground then an additional 10% to 20% of fertiliser would be beneficial.

Fertiliser Programme

Adding manure the previous autumn at a rate of a barrow load of 20Kg per square metre will provide the starting point for the calculation. The manure is around 0.7% nitrogen so you have added 140g of nitrogen. However, nitrogen washes out of the soil and only around 10% of the amount you added is going to be available to the crop. So we've actually added 14g /M2 of nitrogen to get the crop going.

As well as nitrogen to form the haulm (foliage) potatoes need a high level of potash for the tubers. A good source of this is to lay wilted comfrey leaves in the base of the trench, covered with a little soil under the seed potatoes.

First Early Potatoes

For first early potatoes the addition of extra fertiliser is probably unnecessary, assuming you manured in the autumn. If you have not manured previously, adding 200g/M2 of Growmore or fish, blood and bone will provide enough to get a decent crop.

Second Early & Maincrop Fertilisers

Second early and maincrop potatoes will certainly benefit from additional feeding prior to planting even if previously manured and again at the point where the tubers begin to form. This is effectively when the foliage canopy between the plants begins to touch.

The reason we are adding nitrogen through the growing season is that nitrogen is the element that has the lowest life in the soil. Heavy rain or irrigation washes it out but phosphates and potash remain to be available for the crop.

A good source of additional potash is wood ashes - if you've burnt some wood pruning then don't waste this valuable resource.

Calcium nitrate applied at 70g/M2 will provide (at 15.5% nitrogen) an additional 11g/M2 of nitrogen plus effectively lime, thereby reducing soil acidification and this will improve total yield, improve the skin finish and improve keeping quality.

Organic gardeners with a lot of comfrey liquid feed available could water weekly or fortnightly around 5 litres per metre of row or add around 100g/M2 of dried blood.

The late maincrop varieties are in the ground longest and these need the most feeding. Adding additional nitrogen around ten to twelve weeks after planting should carry them through.

Potato Information

• Brief Guide to Growing Potatoes
• Potato Varieties for Flavour, Boiling, Roasting, Mashing, Chipping etc.
• Potato Fertilizer Programme
• Potato Blight - Identification and Treatment of Potato Blight
• Harvesting and Storing Potatoes