Heat, Hotter, Hottest

heat and the gardenPlants find it tough in these conditions as well. Arid plants are adapted to long periods of Saharan conditions but we don’t grow xerophytes in our community garden! Storing water in cells (succulents), reducing leaf area, waxy or hairy leaf coverings and shallow, extended roots systems are some of the plant adaptations in arid zones, as well as altered photosynthesis (CAM) where the plants can close the stomata on their leaf surfaces and still be photosynthesising, albeit very slowly, a bit like an idling car, by using stored gases in the leaf cells. No doubt plant breeders are working on developing these traits in our dryland crops as the climate changes.

In the meanwhile, we have had to take some more direct action to protect our food plants in heatwaves. We’ve been rigging up makeshift shade, hanging wet coffee bags, old lace curtains and even mossie netting over some of the more heat sensitive plants (esp. berries) and putting the drippers on at night, giving everything a spray to reduce temperatures on their leaf surfaces morning and nght. Gen especially has been on double duty.

_DSC0076It’s a bit like deciding which of your prized animals to keep as the drought bites – you need to consider which are your most important plants (established and young fruit trees, perennials, plants in production, plants that have several functions) and what you are prepared to let go (sensitive annuals that can be regrown, eg. lettuce and those that are water needy) because in some cases a week of extreme heat will set back  growth and production so much that it’s probably not a wise use of water and human energy to try and keep them alive. You will know which plants are your precious ones.

Heat affects photosynthesis. Most garden plants need to keep the stomata on their leaves open in order to transpire (reduce cellular temperatures – our equivalent of sweating?) and also for photosynthesis, where gaseous exchange occurs – carbon dioxide CO2 in, and oxygen O2 out. It’s a bit more complex than that, but basically:

6 CO2 + 12 H2O + photons → C6H12O6 + 6 O2 + 6 H2O (carbon dioxide + water + light energy → glucose + oxygen + water).

leafWhen plants are stressed – eg. heat, wind – they will close their stomata, which means they are not photosynthesising, not growing, not ‘breathing’ and therefore prone to further illness, disease or insect attack, which means they will close their stomata … and so on. Plants that are already stressed by things like cherry and pear slug (which we have on our pears this year – see Megan’s comments) or fusarium wilt will decline further. We can help them by keeping the leaf surfaces cool, keeping moisture up and providing a ‘tonic’, like a drink of seaweed solution or diluted wormjuice, or both.

Have a look at these earlier posts for some more tips: protection, watering.

Observations by BD growers during the long drought were that biodynamically managed farms withstood conditions better than their conventional neighbours, and I reckon the four years we have been applying the BD preps will stand the garden in good stead too, with improved water holding capacity and soil life.

Our garden seems to be surviving ok, thus far, but it’s still fingers crossed, and hoping that our plotholders and gardeners will help the plants and trees survive this week (and the hot weeks ahead…) After all this is over, we’ll be ready to do some summer pruning (thanks to info from the Garden of St Erth workshop)…  and hopefully the trees will still be happy and healthy.

Read about summer pruning.

4 thoughts on “Heat, Hotter, Hottest

  1. megan says:

    Just wondering what best to do if I have a question or comment on something noted in garden? Write on a board in garden/greenhouse? On blog? I have not run into people in garden and don’t want to clog up people’s inboxes

    For example, was wondering how people have mixed up lime spray in past as slugs on pear and back fruit trees ( and on trees at home!). Also noted the fruit trees and bushes on sprayers could do with a go

    • janet barker says:

      Hi Megan
      Both methods would probably be best!
      The blog will certainly – hopefully – be answered but not sure if every gardener reads it.. hopefully the regular gardening sessions will also help once we start them…
      We haven’t done it in the past as it hasn’t really been bad enough. But at the pruning workshop yesterday one gardener said she just sprinkles white flour on her trees (repeats after rain). the flour clogs up/dries out the pesky slug – make sure you cover the leaves where they are hanging out.
      This may be most benign and easiest for now.
      you can also use (sieved) wood ash (if you’ve had a wood heater over winter and have saved the ash somewhere dry) or normal (sieved) lime in the same way, but will need a mask (we may have some at garden) and stand down wind!
      You can also dilute the lime – preferably builders (slaked) lime for this version – I’d suggest diluting a handful in 10L of water and mixing as well as you can, pour through a sieve/fine mesh into sprayer and try that.
      Those small trigger bottles would work for the lime spray there’s also another larger poly pressure-pump sprayer but i had trouble with the leaf curl spray clogging in it last time (may need to put a second filter sieve in it?)
      You can also see why we haven’t done it before!!
      We do need to get on top of pest control this year. More companion planting??

      • Julia E says:

        I haven’t checked recently, but I am wondering how the slugs are faring after this extreme heat. I was once advised by the head gardener at the Castlemaine hospital that there was no need to worry about the pear and cherry slug as the following day was expected to be over 40 degrees. Being such moist creatures the slugs could not survive the dry heat. If that is correct we should have no slugs left after the past week

  2. megan says:

    Thanks so much for the reply Janet. Yes the flour sounds like an easy option to try. I will give it a test on quince tree at home which is quite bad. Companion planting is very interesting and considering some more combos in the community garden this year would be a bit of fun!

    One last comment about cherry slugs.Seems we may be seeing the ‘second generation’ summer slugs and it is good to hit first gen in spring. Flowering shrubs and flowers around fruit trees help to attract slug eating insects and wrens: http://www.organicgardener.com.au/blogs/pear-and-cherry-slug

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