Potato
7 Apr 2022
Solanum tuberosum
The most popular vegetable in Australia and the fourth largest food crop in the world. If you’re a fan of potato, you’re not alone. Potatoes are familiar as a tasty, versatile starchy food that stores quite well for a long time. They are relatively quick to grow for their tuber size, taking 12 – 18 weeks / 3 – 4.5 months.
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Unfortunately they’re not super fond of the conditions in our area. These are an annual cool climate plant. However, they can be grown here. They are even grown commercially in the Bellinger valley. They just aren’t a set and forget kind of plant here like they tend to be in more appropriate growing locations such as Dorrigo, Victoria, Scotland, NZ, or the Andes which is where they’re from.
Potatoes don’t like humidity.
They prefer a drier-aired climate. They already have a laundry list of about 60 pests and diseases under ideal conditions, without subjecting them to an environment they don’t like and dealing with rampant pathogen growth in our subtropical humidity.
Potatoes don’t like warm soil or nights.
They grow best in soil temperatures between 15 and 20°C. Planting at temperatures below 10°C means hello soil borne diseases. Soil temperatures above 26.5°C means far fewer tubers. Over 29°C tubers don’t form.
Warm nights also mean that tubers won’t form. This is a big reason spring planted potatoes in this area can fail. The plant does not get the down-time to store the energy it collected during the day into tubers. Instead it stays active and burning energy over warm nights. In cool springs this is not an issue.
Potatoes don’t like large dumps of rain.
They are fussy about receiving even watering and don’t cope with water stress – too much or too little. They rot in our monsoonal downpours.
Potatoes are damaged by frost.
The tops will be knocked back by the light frost in this area, but it shouldn’t be a major problem. They tend to bounce back. And they can be protected through the cold months if you want. Place them in a frost free area. Use frost protective row covers. For young plants, lightly/partly cover the tops with straw mulch to give a layer of insulated protection.
The best times to plant potatoes in this area, according to local growers, are April, May, June & July. This is so they will be out of the ground by the time our humid hot season rolls around come November. Tubers form in response to shortening day lengths, and cool temperatures. Although breeding has minimised this day length tendency and potatoes can be grown in spring (lengthening days), it is worth noting that their natural growing season is autumn.
Commercially for coastal potato growing areas of NSW (Grafton to Windsor near Sydney) there are considered to be two planting times – June, July, August for harvest October to January. And another time in January and February for harvest June – August. This advice obviously covers cooler areas than ours.
There are in the region of 5000 varieties of potato. So many to explore!! For eating, potatoes are often divided into waxy (16 – 18% starch) – great for boiling, and floury (20 – 22% starch) – great for baking.
Commercially in Australia, Atlantic and Sebago are the most tolerant to high growing temperatures. From the QL Potato Information Kit, “Sebago withstands extreme conditions of heat and moisture very well, and is particularly suited to heavier alluvial soils. It has low resistance to wind and frost. The variety is particularly versatile and can be used for all purposes…. The tubers can be boiled, mashed, fried, deep-fried, roasted and baked when fresh.”
A number of people interviewed expressed the opinion that the various purple varieties of potato seem to be hardier and more reliable in this area compared to other varieties. Purple Congo was mentioned. Sapphire is another commonly available purple variety.
Potatoes are grown from a previous crop of potatoes, not from seeds. These tubers-for-planting are called seed potatoes. While you can plant any sprouted potato from the store, that’s running the risk of introducing an unwanted range of problems. Potatoes are potential little bombs of plant disease and gardener despair. They are prone to blights and wilts that stay living in the soil. Potatoes are in the same family as tomatoes, capsicums and eggplants and all are susceptible to the same pathogens. Ideally, buy seed potato that has been certified as disease free.
Seed potato should be kept in cold storage of 4 – 5°C with 90 – 95% humidity and airflow around them ie not in bags. This keeps them dormant which means they will store for longer and be ‘younger’ than seed potato that was not kept dormant. Plants grown from physiologically old seed are stunted, very susceptible to disease and only make a lot of small tubers. To break dormancy, bring the seed potatoes into dark, warm, humid conditions a few weeks before planting. This will trigger them to begin growing sprouts from the eyes. And then they are ready for planting.
The seed potato, either whole or in pieces with at least one sprouted eye each, need to be at least 5cm in diameter. Any smaller and the plant won’t have enough energy to grow properly and make lots of large tubers. It relies on the seed for the first month of growth. Pieces with cut edges can be planted immediately into damp soil if it won’t rain before the leaves appear (2 – 5 weeks), or allowed to air dry and heal before planting.
There are as many methods to grow potatoes as there are gardeners. Deep trenches. Hilling up. Potato bags and bins and cages. Straw bales. They all work. These are the puzzle pieces which need to be solved to grow potatoes successfully:
How to sow
The seed potatoes should be planted 10 – 15cm deep and 20 – 30cm apart. Don’t plant potatoes in the same place for 3 – 4 years to minimise disease buildup. Each potato plant should create 10 – 14 tubers.
No wind or frost.
Potatoes don’t cope with wind. Make sure they are sheltered. They are knocked back by frost, but do recover. A frost free location is ideal.
Keep tubers underground.
Tubers exposed to light react to protect themselves from sunburn by turning green and producing toxic compounds. Green potatoes are poisonous to eat. It only takes a day of a tuber being exposed to light for this to happen.
Provide as much growing room as possible between the seed potato and the soil surface.
Super important.
The potato plant grows upwards from an eye on the seed tuber. New tubers form off the part of the stem that is underground and above the seed tuber. The more underground stem, the more potential tubers. This is the reason many methods involve planting the seed potato, and after the leaves emerge, gradually adding more soil or straw on top, to make more underground stem for tubers to form off and more space for the new tubers to grow.
Loose friable soil.
Potatoes need a loose soil to create big and regular shaped tubers. Compacted, clod filled soil results in smaller and alien shaped tubers. Weeds love this soil and potatoes will need to be kept weeded over their entire growing time.
Great drainage.
The growing tubers will rot if they sit in waterlogged soil. Hilling up, straw bales, potato bags, bins or cages should prevent this.
Even watering.
As mentioned before, potato plants are fussy about water availability. They have a surprisingly shallow root system for the size of plant and the amount of creation they are doing, only 30 – 40cm deep. Ideally their soil is moist, but not wet, all the time. The most critical stage for water stress is when tubers are first forming, and again as they are bulking out. This is covered by weeks 7 – 16. Anytime from week 12, the potato tops will start to lose vigour. This is the sign they are nearly mature and all watering should stop.
Feeding.
Potatoes love rich soil with lots of compost and potassium. The roots, below the seed potato, need access to the food. The area between the seed potato and the surface can just be straw. It’s the roots that need to be well fed. It’s best to make sure there is plenty of food before planting. Potatoes need a fair amount of nitrogen, especially in their early stages. But too much just makes loads of tops and no tubers.
How to tell they are ready.
From 12 weeks after planting, the potatoes may be ready and are worth checking. They should be done by 18 weeks. Bandicoot down and rub the skin of the new potato tuber with your thumb. If it doesn’t rub off easily, it’s time to pull them all out. Another sign is the leaves begin to yellow and die down. But don’t wait for all the leaves to die down as a decent number of potatoes may have already gone to mush by then. It’s best to dig the cache of potatoes up in cool temperatures and move immediately into a cool dark location as this helps them store for longer.
Big thanks to:
Ken Lewis from Stringybark Farm, Jeff Holmes, Angelle Hughes, Paul from Barefoot Fruit & Veg, Tim Hill, Pete Bufo, Nick Radford from Bellingen Permaculture, Kyles Woodbury formerly of The Vegie Gardener, John Hodgkinson, Ian Thomas from The Gourmet Garden School, Charles Filet, Carole Helman & Phil Gilmour.
Supported by Bellingen Shire Council via the Bellingen Shire Disaster Recovery and Resilience Grant Program Funding
Notes
1. Jackson K, Kerr J, Kilpatrick J, Henderson C, Lovatt J. Potato Information Kit. Agrilink, your growing guide to better farming guide [Internet]. Queensland Horticulture Institute. Brisbane, Queensland: Agrilink Series QI96084. Department of Primary Industries; 1997 [cited 2022 Apr 1]. Available from: https://era.daf.qld.gov.au/id/eprint/1658/
2. Wade S. The potato industry in New South Wales. 2008;7. Available from: https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0003/315381/The-potato-industry-in-New-South-Wales.pdf
3. Potato Crop Nutrition – Fertiliser for Potatoes – [Internet]. Yara Australia. 2018 [cited 2022 Apr 1]. Available from: https://www.yara.com.au/crop-nutrition/potato/
4. Potato – Wikipedia [Internet]. [cited 2022 Apr 4]. Available from: https://en.wikipedia.org/wiki/Potato
5. Cundell P. Spuds don’t fear frost [Internet]. Weekly Times. 2017 [cited 2022 Apr 7]. Available from: https://www.weeklytimesnow.com.au/country-living/gardening/peter-cundall-spuds-dont-fear-frost/news-story/2fbf452cd38d85631eb45bc3c306dde5
6. King C. Heat-Proofing Our Potato Crops [Internet]. Spud Smart. 2020 [cited 2022 Apr 7]. Availale from: https://spudsmart.com/heat-proofing-our-potato-crops/
7. Buy Online Seed Potatoes [Internet]. Green Harvest. [cited 2022 Apr 7]. Available from: https://greenharvest.com.au/Plants/Potatoes.html
