Kūmara gardens were known as māra kūmara. They consisted of puke (mounds) formed from loosened soil, arranged either in rows or in a recurring quincunx pattern (the shape of a ‘5’ on a dice). Kūmara tubers were planted in the mounds. Sloping land with a sunny, northerly aspect was considered ideal.
Relatively light, sandy soils were preferred for growing kūmara. In areas with heavier soils, people added gravel and sand – sometimes moving these materials long distances to very large gardens.
It is thought that the gravel and sand allowed better drainage, so crops could be planted earlier because the drier soil warmed up more easily – or that the sun warmed up the stones and warded off the damaging effects of frost.
In some areas, the remains of extensive gardens can be seen, with rows of stones that are thought to be boundary markers. In some places stones are piled into mounds instead of rows, and in others there are both mounds and rows. It is not clear what their function was. Crops may have been grown in soil on top of the rocks, which helped regulate the temperature. Alternatively, the mounds and rows may have been left when garden areas were cleared, with crops planted in between.
Simple fences were built around gardens to act as windbreaks and keep out pūkeko birds. Kūmara were attacked by caterpillars of the sphinx moth (kūmara moth), and Māori often tamed seagulls to eat the caterpillars. Sometimes fires were lit and kawakawa leaves thrown on to smoke out the caterpillars.
Diminishing garden plots
Kūmara could be grown in one place for only a limited time before soil became depleted of nutrients. Another garden had to be started elsewhere and the original left fallow so the soil could regenerate. In tropical Polynesia, rotational cropping could be easily maintained over a 20- or 25-year cycle that eventually returned to the first garden plot. However, in New Zealand, bracken fern often colonises bare land, forming a tangled web of stems and roots which is difficult to eradicate. The plant was hard to dig up, and burning did not work, as it regrew from the roots. Kūmara gardens that had been used earlier became largely unusable because of bracken. New plots had to be found, and suitable land eventually became a diminishing resource.
Return of the kūmara
In 1969, a New Zealand-based collection of hundreds of kūmara varieties was sent to Japan for safekeeping. In 1988, on a trip supported by British botanist David Bellamy, members of the Pū Hao Rangi trust brought nine cultivars back to New Zealand. Three of these – taputini, rekamaroa and hutihuti – may date from before European arrival in New Zealand. DNA analysis is being used to study their provenance.
In the 19th century, traditional kūmara grown by Māori were quickly superseded by larger and higher-yielding sweet potatoes from North America, brought by sealers and whalers. New Zealand’s commercial kūmara crop is based on three more recent cultivars, the Owairaka Red, Toka Toka Gold and Beauregard, all of which produce tubers about 20 centimetres in length.
Growing kūmara commercially
In the early 2000s, there were about 85 commercial kūmara growers, mostly in Northland. Around 20,000 tonnes were produced annually from 1,220 hectares of plantings, mainly for domestic consumption.