6 reasons why this tree is a favourite shelter option on Nuts 'n May

There are many types of shelter trees on Hel's Whanganui block, but one stands above all others.

Alders are the favourite of her mother Diana Loader, a legend in NZ tree cropping circles. She established the trees on the farm with husband Walter when they bought the land in 1987.

Diana started from scratch, sowing the seeds, potting the seedlings into root trainers, then planting them out. She got an almost perfect strike rate – "I lost two out of 6500".

She's very fond of alders for several reasons:

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lots of varieties to suit different climates and soils;

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easy to grow from seed;

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they grow a centre stem – "like a carrot, nice and straight", says Diana – but have small side branches, so they're easy to prune and don't form big bushy tops;

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their roots go deep, so they don't rob nutrients and moisture from surrounding plants, such as grass;

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they're deciduous, letting in light over winter.

The key to their success as shelter is regular pruning. "Our alders took no damage (in a big 2012 storm), but they're all pruned," says Diana. "Every year, we cut them down to 20ft (6m) – they grow 10ft (3m) every season and we cut that off. We do have some unpruned alders that stood up to the wind though, they're about 40ft (12m)."

The timber quality isn't an important criterion for Diana, but it's pretty impressive.

"It's excellent. The piles of the city of Venice have been underwater for 500-600 years and they're all alders, so I believe."

Depending on your location, good varieties include:

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South Korean alder (Alnus japonica);

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Red alder (Alnus rubra);

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Grey alder (Alnus incana).