Gareth Carter: Make this the year you plant potatoes

Gareth Carter and his son planted a crop of potatoes behind a young griselinia hedge.

With vital growing areas of our country being affected by floods and cyclones, this is a good year to grow your own potatoes.

They are a fairly quick returning crop, taking about three to four months from planting to harvest. In the post-war years, it was common that the bank and/or front lawns of properties were dug over by hand and planted in rows of potatoes to feed the family for many months of the year. It is worth thinking outside the square as to where you may be able to plant your crop. Last year my son and I planted a crop in a space behind a young griselinia hedge.

We don’t often see this these days but maybe in the current economic climate this could be a good thing to do. Not only can it be good for the wallet but also our bodies - digging, bending and planting is all good exercise to strengthen the body. Being outside in the fresh air, gaining vitamin D from the sun, will help our minds and our mental health against the worries of this world.

New season seed potatoes have arrived in stores. Now is the time to choose the varieties you want, take them home and allow them to grow sprouts ready for planting out early next month. Once they have been mounded a few times it will be past the time for late frosts or they can be covered with frost cloth if a rogue one seems likely.

It is important to select a good spot as potatoes need a sunny - at least five hours a day - position where they will not be competing for moisture. They also benefit from being in a sheltered area that does not receive strong winds.

Next, the soil needs to be “well worked” – this means it has been dug over to a depth of 25-30cm. This will allow the potatoes to grow and multiply. If it is very heavy, clay-like soil, creating raised beds to ensure good drainage will be beneficial. If, on the other hand, the soil is very sandy, the addition of organic matter such as compost or sheep pellets will be beneficial as they not only add nutrients but will also help hold moisture for longer. Potatoes are a tuber that forms on part of the stem that is underground. By “mounding up” soil around the stem as the plants grow you will increase the amount of stem underground and the yield from each potato plant.

What are the economics of growing potatoes? As a benchmark for you, each seed potato planted can yield 15-25 potatoes. So a 2kg bag of seed potatoes (containing around 24 potatoes) will yield 360-600 potatoes (45-75kg). So, if you have space available, give growing potatoes a go.

A number of potato varieties are available. The way to choose which one to plant is to know when you want them mature and how you like to eat your potatoes. Have a look in-store and check out the varieties. Three favourite varieties are agria, heather and jersey benne. Agria is an early main cropper and has a long oval shape with yellow flesh that is perfect for roasting, chips and wedges. Heather is a main crop potato that is oval and has a distinctive purple skin with white flesh – it’s great for boiling, roasting and casseroles. Jersey benne is an early variety with a kidney or oval shape, whose white skin and flesh is excellent for mashing or boiling.

If you do not have enough space in your garden for a row or two of potatoes, you can grow them quite successfully in containers, large plastic bags or a bucket (say 35 litres) using a good quality mix such as Tui Vegetable Mix. Make sure there are plenty of drainage holes. Place tubers in the potting mix near the bottom of the container, covering them by about 50mm. As the sprouts grow, keep adding the vegetable mix until it is up to the brim of the container, add a dressing of Ican Vegetable Food each time the vegetable mix is added or some Tui Novatec every two months. Harvest when the tubers are ready.

The often-asked question is “do I need seed potatoes or can I plant a few potatoes left in the bottom of the pantry that I purchased from the supermarket?” The answer is to purchase “certified seed potatoes”. This means the seed has been assessed by an authority called Potatoes NZ. This certification is to ensure the seed is free from viruses that can significantly reduce the yield.

Here is an easy seven-step process for delicious homegrown spuds. Ensure you select varieties that suit how you like to eat your potatoes as some varieties will roast well, while others are excellent in potato salads.

Step 1

Site selection, taking into account the factors previously discussed (sun, moisture and wind).

Step 2

Purchase certified seed potatoes, spread out in a warm light location and leave to grow sprouts (around three weeks).

Step 3

Prepare the soil for planting. Remove any weeds from the area and dig over the soil to 25-30cm deep, working the soil to a fine texture. Spread both potato fertiliser and garden lime over the soil and mix well so none will come into direct contact with the potato tubers when they are planted. Add gypsum to the garden if the soil is clay and raise the bed to improve drainage if required. If the soil is very light, the addition of compost or sheep pellets will improve moisture retention.

Step 4

Plant seed potatoes around 10cm deep, 35-45cm apart and in rows about 75cm apart. This gives a good amount of space to later mound up soil around each plant.

Step 5

Check weekly. When shoots have emerged and are reaching 20cm high it is time to start mounding. Mound up the soil, almost completely covering plants, and continue to check regularly. Once they have grown another 20cm mound them up again. Having so much of the stem covered will ensure a decent crop as tubers form up the buried stems. Sprinkle the soil around the plants with potato fertiliser each time before you mound up the soil. By covering the stems of the plants with soil you are also providing protection from any late frosts. Any tops remaining should be covered with frost cloth if a frost looks likely.

Step 6

Pest control and care. The potato/tomato psyllid has become a problem. The symptoms often don’t show up until it is too late as the insects can only be seen under the microscope. However, it is easily controlled using Yates Mavrik or Yates Success Ultra on crops growing from November to April. If you like to avoid using sprays, I suggest planting sooner rather than later as the insect problem becomes more prevalent as summer progresses (December onwards). By starting your potato crop now they will likely be ready for harvest before needing treatment for psyllid.

Step 7

Harvest. You know your potatoes are ready for harvest when the plants flower. A few varieties, such as rocket, do not flower so in this situation it can be useful to mark on the calendar when they would be due. Generally, early varieties will be ready to harvest around three months from planting while four months for late and main crop varieties is more suitable. The later and main crop varieties are usually better for storing.

For more gardening information visit www.springvalegardencentre.co.nz

* Gareth Carter is general manager at Springvale Garden Centre.