Plants 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.
It’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).
When 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.
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.