Grow­ing me­dia _______________________________

The first article I ever wrote for the NZ Com­mer­cial Grower (the pre­de­ces­sor of the NZGrower) was pub­lished nearly 60 years ago.

NZ Grower - - Election 2017 - Mike Nichols

This was writ­ten as a raw (very raw) ex­ten­sion of­fi­cer when I was ini­tially based in Oa­maru in 1958. At that time there was a buoy­ant green­house tomato in­dus­try based around Oa­maru (mainly at Kakanui), as pro­duc­tion in New Zealand was very much based on lo­cal, rather than im­ported (from the North Is­land) pro­duce. How­ever the North Otago tomato grow­ers had one ma­jor prob­lem. The pre­dom­i­nant soil type was the so called “tar” soils de­vel­oped from an un­der­sea vol­cano many cen­turies ear­lier. Ex­cel­lent for grow­ing out­door veg­eta­bles, but ex­tremely dif­fi­cult to fu­mi­gate us­ing methyl bro­mide or chloropi­crin, as the gases re­mained locked up in the soil.

For this rea­son the green­house soils were ei­ther steam ster­il­ized or re­soiled be­tween crops. Steam­ing was very ex­pen­sive (but a safe strat­egy) while re­plac­ing the green­house soil (to a depth of 30 cm) was a risk, in that it was quite pos­si­ble to bring in dis­eases or pests with the new soil, and in any case al­though the yields from the new soil were higher than nor­mal, the qual­ity of the fruit tended to be lower due to the lower fer­til­izer (par­tic­u­larly potas­sium) lev­els.

An­other al­ter­na­tive strat­egy, in­volv­ing much less soil move­ment, was to fill up old kerosene tins with new soil, and put these on the glasshouse floor, thus not only mov­ing far less soil, but also en­sur­ing in the cold North Otago win­ters, that the root zone was kept much warmer than by plant­ing directly in the green­house soil. The idea of us­ing an im­proved soil to fill the kerosene tins was at that time con­sid­ered much too ex­pen­sive.

We have come a long way since then. Rock wool slabs im­ported all the way from Europe, or coir mod­ules pro­duced in Sri Lanka or In­dia have be­come the norm for the ma­jor­ity of green­house crop pro­duc­ers, and the re­wards of us­ing a high qual­ity stan­dard grow­ing medium have be­come ap­par­ent.

Sev­eral years ago I at­tended a con­fer­ence on grow­ing me­dia in Barcelona, Spain at which it was stated that there was go­ing to be a world short­age of the ba­sic raw ma­te­ri­als which make up good hor­ti­cul­tural grow­ing me­dia. The prime or­ganic com­po­nent of grow­ing me­dia have in the past been peat, which is now un­der pres­sure from en­vi­ron­men­tal­ist. The prob­lem is that al­though there is plenty of peat in the world (in fact it is ap­par­ently be­ing re­placed at a faster rate than it is be­ing used) this re­place­ment is oc­cur­ring in dif­fi­cult of har­vest (mine) places such a north­ern Canada/Fin­land etc, and the easy to har­vest places are be­ing over­har­vested.

The con­cern about fu­ture sources of or­ganic mat­ter was so se­ri­ous that con­sid­er­a­tion is be­ing given to grow­ing trees, sim­ply to pro­vide a sta­ble, re­li­able long term source of or­ganic pot­ting medium.

New Zealand is very for­tu­nate in that we have a ready made source of or­ganic pot­ting me­dia in the bark from the pine trees har­vested for sale as tim­ber, and have de­vel­oped a very ac­cept­able method of treat­ing this Pi­nus ra­di­ata bark for use as a grow­ing medium.

Un­graded, un­pro­cessed pine bark. New Zealand’s grow­ing medium for the fu­ture?

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