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My old blackcurrant bushes are average in production. The ‘Ben’ varieties are said to have heavy crops of much larger currants. Which variety would be best for us? We have heavy soil but good summers. A R MILLAR, WAIPUKURAU We consulted Geoff A Langford from Berryworld Ltd who ran the New Zealand blackcurrant breeding programme at Lincoln University for many years. The programme produced a whole range of varieties which are now widely grown commercially.
The research had a strong focus on varieties that had lower chill requirements to cope with our temperate climate. Amongst their most successful varieties are ‘Murchison’, ‘Blackadder’, ‘Melina’, ‘Isabel’, ‘Kepler’ and ‘Victoria’. Geoff’s personal favourite is ‘Isabel’ as it makes beautiful jam and is great in muffins, but it is slow to establish.
The ‘Ben’ series of blackcurrant varieties were developed by Scottish Crop Research Institute (now the James Hutton Institute). All of the varieties developed by their breeding programme have a ‘Ben’ prefix. In the 1980s some unnamed material was sent by SCRI to New Zealand where it was tested and two of the selections were found suitable for New Zealand conditions and released as ‘Ben Ard’ and ‘Ben Rua’. These two are not grown anywhere else in the world and they have become important varieties because of the high anthocyanin content (the antioxidant which gives currants their dark colour and health benefits). Both have a relatively low chill requirement. ‘Ben Ard’ is still widely grown from Canterbury south and can be grown in the central North Island and most South Island areas. (but apparently it struggles in coastal Nelson because of the lack of chill). ‘Ben Rua’ is okay for lower chill situations but is quite tricky to grow.
‘Ben Mapua’ was one of the original releases from SCRI selections but it didn’t succeed commercially and was variable in performance with lowish anthocyanin levels but big fruit.
The key is to find a variety that will perform in your local climate. Try a few different cultivars (not ‘Magnus’ as it is marginal for winter chill and in general a poor performer).
A good way to find a variety that copes well with the soil and the specific winter chill for your area is to get in touch with local garden club or local branch of Tree Crops Association (treecrops.org.nz) or use Neighbourly (neighbourly.co.nz) to find someone nearby who’s happy to share a cutting from their own productive blackcurrant bush. It might not be a named variety but you know it does well in your region.
You could lavish some TLC on your old bushes to try and up their yield too (although best production can be expected for a 10 year period after the plants have been in the ground for four to five years). Fertilise with 30g citrus fertiliser per bush in early spring and mulch to retain moisture.
Prune to maintain size by removing old stems to a new low bud, removing at least a third of the old cane. Aim to have 8-10 shoots per bush. No cane should be in place longer than three years. Encourage new shoots by cutting down old wood to new buds in winter.