Brisbane Local Food

Growing local

Just curious as to whether anyone does anything to extend the growing season around here?  Most of the online growing guides talk about using cold frames or poly tunnels to extending the period that your plants are able to ward off freezing solid.  But for me, I'd really like to grow some more cool weather crops for more of the year, and there's not too much information around apart from increasing shade.

I had the idea of planting in a zeer pot.  A zeer pot is an evaporative cooling refrigerator made by putting a pot inside a larger clay pot, with a water reservoir in between.  The water slowly seeps through the clay and evaporates from the surface, cooling the entire vessel and keeping food inside the inner pot cool.  It works best at low humidity, and not at all at 100% humidity, so they are generally written off for use in the humid subtropics.  Here's an explanation including a table of the effectiveness at various ambient temperatures and humidities.  But what if...

What if instead of using it for food storage, you put soil in the inner pot and planted into it?  You could use a clay pot for the inner as well and get the advantage of an all-around olla keeping the soil moist, although you'd have to do a bit of finagling with the drainage holes to make sure it didn't get waterlogged.  And while on humid days, you wouldn't get too much in the way of cooling effect, you'd generally get a bit.  At an average of 70% humidity, you'd get maybe 5 degrees lower in the soil temperature, at 30% humidity you might get 10 degrees lower.  Surely that would be enough to encourage the development of the occasional carrot or iceberg lettuce when they're pushing the border of the season?

And then... what about fruit trees that need a higher chill factor than you can provide them in Brisbane?  Obviously getting hold of low chill is best, but if something you want is a little borderline, what about planting it inside a pot like this, siting it in a location where it gets summer sun only, and letting the cooling effects of the pot keep it happy during summer--but then bring down the temperature even further over winter, at which time it which will be significantly less humid and thus more effective?  Of course the soil would be the coolest point (is it the roots or the branches that need to accumulate chill?) but the evaporative cooling would also reduce the ambient temperature in the vicinity around the branches to some extent as well. Do you reckon that might increase the chill accumulation?  Or even putting a "reverse olla" on or in the ground next to a tree that's not accumulating as much chill as you'd hoped it would or it used to?  Food for thought.

What do you folks think?  And what are your tips and tricks for extending the growing season for cooler crops?

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Comment by Dave Riley on December 27, 2019 at 13:14

I have aerials I grow various climbers on -- beans, squashes and gourds mainly. So I use shade to manipulate the seasons. Cut back/let grow according to needs and preference. 

In my experience the most useful climber for manipulating  shade in Summer is choko.

Mulch too will effect soil temperature below it -- cooling it in hot weather.

Also get yourself a soil thermometer and play with that.

Moisture will also cool the soil. I'm on sand all the way down and contrary to  standard advice I water frequently for short periods and over night.

I'd also expect that watering via sprinkler -- as I do -- is more cooling of the plants, compared to drip irrigation.Think micro-climate and you gotta get the water airborn.

The mulch too will stay cooler longer than bare soil.

I used to use terracotta pots to irrigate my garden. I still do use that system for my milk crate beds. If you keep the water up, they will have a chilling effect in the growing zone surrounding them. But make sure you shade the tops from evaporation. I use shade cloths. One layer will do once the plants grow.

When it comes to the leaf veges the old trick is to plant them in Styrofoam boxes and move them around -- chasing shade -- during summer.

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