Blue­berry magic

My first in­volve­ment with grow­ing blue­ber­ries in a green­house was some 15 years ago, when I grew a wide range of va­ri­eties at Massey Univer­sity in coir slabs.

NZ Grower - - FEATURE - By Mike Ni­chols

It was very much a look see, and we learnt a lot of im­por­tant lessons from what was glob­ally a very new crop for pro­tected cul­ti­va­tion. I sus­pect that it was only the sec­ond crop of blue­ber­ries ever grown in a green­house, and the very first ever grown hy­dro­pon­i­cally.

Our ex­pe­ri­ence clearly demon­strated the im­por­tance of net­ting to keep out birds – the black­birds used to sit on the ven­ti­la­tors and fly into the green­house for break­fast when the au­to­matic ven­ti­la­tors op­er­ated each morn­ing once the fruit ap­proached ripeness.

Our sec­ond les­son was the need to use a low pH (4.5) for the hy­dro­ponic nu­tri­ent so­lu­tion to re­duce the risk of iron de­fi­ciency. Fi­nally, and some­what sur­pris­ingly, we found that there did not ap­pear to be a need for win­ter chill to en­sure flow­er­ing and fruit­ing, even though we were us­ing a wide range of va­ri­eties – from those de­vel­oped for sub-trop­i­cal Florida to those adapted for ex­tremely cold win­ters such as in up­per New York State. Clearly a fac­tor which re­quires fur­ther ex­am­i­na­tion.

A few years later I met a Mex­i­can grower at a con­fer­ence in Ari­zona, and he of­fered to show me some of the out of sea­son berryfruit be­ing grown in the moun­tains near Guadala­jara. This was my first ex­pe­ri­ence of see­ing blue­ber­ries be­ing grown out of sea­son un­der high tun­nels, with bird-proof net­ting. How­ever the plants were not grown in the soil, but us­ing a coir mulch.

Un­like most berryfruit, blue­ber­ries can best be de­scribed as sim­i­lar to ball­bear­ings in terms of ro­bust­ness, so the eco­nom­ics of us­ing rain shel­ters (high tun­nel green­houses) must be considered a lit­tle sus­pect, ex­cept that har­vest­ing in the rain can be a prob­lem, and con­trolled ir­ri­ga­tion is far su­pe­rior to let­ting na­ture take over. In any case a sup­port for bird-proof net­ting is an es­sen­tial part of in­ten­sive blue­berry pro­duc­tion.

Al­though many of the orig­i­nal green­house blue­berry crops were grown in soil, in re­cent years there has been a move to­wards high qual­ity

grow­ing me­dia. In a re­cent study in the Netherlands (Ta­ble 1), grow­ing blue­ber­ries in a well for­mu­lated grow­ing medium demon­strated clear ad­van­tages in yield com­pared to grow­ing them in soil. Study by Peter van Dyke, Blue­berry con­sul­tant, Netherlands.

This (of course) poses the ques­tion of what is the ideal grow­ing medium for hy­dro­ponic blue­ber­ries. Dal­tons sup­ply a grow­ing medium which com­prises pre­dom­i­nantly com­posted bark mixed with pumice and some coir, whereas in much of Aus­tralia a coir/per­lite mix­ture tends to pre­dom­i­nate. In the fi­nal anal­y­sis the key fac­tors are likely to be pro­vid­ing the ap­pro­pri­ate mois­ture hold­ing and aer­a­tion char­ac­ter­is­tics through­out the life of the crop, which will re­late very much to the sta­bil­ity of the or­ganic com­po­nents of the mix. Nu­tri­tion should not be a prob­lem with hy­dro­pon­ics, but care must be taken to avoid the buildup of ex­ces­sive salts in the medium.

Plant ma­te­rial is a fas­ci­nat­ing sub­ject, as there are now a wide range of blue­ber­ries in this coun­try: the Driscoll va­ri­eties, the large fruited va­ri­eties from Moun­tain Blue Or­chards in Aus­tralia, the va­ri­eties bred in New Zealand by Plant & Food Re­search, and the older va­ri­eties im­ported ear­lier from the United States. Only time will tell which are best adapted to New Zealand con­di­tions. What is clear, how­ever, is that there is a po­ten­tial risk in us­ing tis­sue cul­tured plant­ing ma­te­rial to estab­lish large com­mer­cial plant­ings un­til it has been used for grow­ing and then con­ven­tion­ally prop­a­gated, be­cause of the dan­ger of mu­ta­tions oc­cur­ring in the tis­sue cul­ture phase.

PRUN­ING

Per­haps the real chal­lenge with blue­ber­ries grown in green­houses is to de­velop a sat­is­fac­tory prun­ing and train­ing sys­tem. >

The only log­i­cal sys­tem I have seen is that used by Costa at their Atherton High­lands site in trop­i­cal Queens­land, where im­me­di­ately af­ter har­vest the plants are cut down to about 30cm, and then the re­growth al­lowed to de­velop to 30cm tall, when the tops of the shoots are re­moved. The re­growth from these shoots is again topped at about 30cm un­til growth ceases. It ap­pears that fruit buds de­velop in the ax­iles of the lower leaves. How this might best op­er­ate in a tem­per­ate cli­mate like New Zealand is not clear, and the ef­fect could be in­flu­enced tremen­dously by whether we are deal­ing with early fruit­ing or late fruit­ing va­ri­eties. Per­haps the an­swer is to de­velop a sys­tem sim­i­lar to the ‘UFO’ (up­right fruit­ing off­shoots) sys­tem used for cher­ries in which the plants are grown in nar­rowly spaced rows, with a wide spac­ing be­tween plants in the row. A main stem (nearly par­al­lel to the ground) is able to pro­duce nearly up­right fruit­ing branches, which are re­placed reg­u­larly in a re­newal sys­tem to en­sure con­tin­ued pro­duc­tion of high qual­ity fruit from young fruit­ing buds. Prun­ing of blue­ber­ries is a skilled op­er­a­tion, and re­duc­ing the de­ci­sion mak­ing re­quire­ments is highly de­sir­able.

HY­DRO­PON­ICS

There is no doubt that given the cor­rect pH (acid­ity/al­ka­lin­ity), along with ad­e­quate mois­ture and nu­tri­ents and a well aer­ated grow­ing medium, blue­ber­ries will grow very vig­or­ously, par­tic­u­larly in high tun­nels. The ques­tion is whether to use a re­cir­cu­lat­ing hy­dro­ponic sys­tem or a ‘wa­ter to waste’ sys­tem. Long term, there is no doubt in my mind that the hor­ti­cul­tural in­dus­try will be forced into us­ing re­cir­cu­lat­ing sys­tems for en­vi­ron­men­tal rea­sons, but in the short term, pro­vid­ing the leachate can be re­tained and used to ir­ri­gate other crops, a non-re­cir­cu­lat­ing sys­tem is­sim­pler. Of course us­ing a hy­dro­ponic sys­tem means that the grow­ing medium does not re­quire any base fer­tiliser. The re­cently de­vel­oped lysime­ter from Au­to­grow of­fers a means of mon­i­tor­ing plant wa­ter use, but it must be placed so that the plants are at the same height as the other plants in the house, oth­er­wise it will tend to ex­ag­ger­ate wa­ter loss. An­other way of get­ting a han­dle on wa­ter loss is to mea­sure the con­duc­tiv­ity of the leachate, and if this starts to ex­ceed 2.5 it sug­gests that the wa­ter­ing regime is in­ad­e­quate.

POL­LI­NA­TION

It goes with­out say­ing that pol­li­na­tion will be re­quired to ob­tain good fruit set, and al­though the gen­eral un­will­ing­ness of hon­ey­bees to op­er­ate in glasshouses does not al­ways ap­ply in plas­tic clad houses, to en­sure good pol­li­na­tion the im­por­ta­tion of bum­ble­bees should be a se­ri­ous con­sid­er­a­tion. In some ar­eas there may well be enough wild bum­ble­bees lo­cally.

▴ (Top right) Blue­ber­ries Atherton Table­lands, Queens­land.

▴ (Bot­tom) Blue­ber­ries, Tau­ranga, note widely spaced rows.

Fig 1: Yield of blue­ber­ries (t/ha).

▴ (Top) Blue­ber­ries in Mex­ico; (Bot­tom) A lysime­ter for blue­ber­ries.

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