It’s ten years since Barbara Pleasant shared her advice on gardening with minimal water. It got me thinking: Doesn’t time fly! It also got me thinking about how our weather has changed. A decade ago ago we were talking about the likely impacts of climate change; today more and more of us are living with its unfolding reality.
Gardeners are working with longer, warmer, drier summers, or at least highly unpredictable summers. My part of the world experienced an exceptionally dry summer in 2018. According to the UK Met Office it was also the hottest on record.
In other areas – much of Australia, Southern Africa and the American South and West, for example – droughts are a fact of life. Play around with the maps on the US Drought Monitor website and you’ll quickly gain an appreciation of how severe droughts have become. Compare the maps below of California in May 2016 and May this year (the darker the colour, the more extreme the drought). You never know when drought will intensify or ease; it pays to prepare for the worst.
How Water is Lost
Keeping plants quenched during the summer requires a two-pronged approach: conserving soil moisture as best we can while applying additional water with care. Understanding how water is lost from the landscape helps us plan strategies that make the most of this precious resource.
Water loss occurs as a result of evaporation, transpiration (water loss from plants), runoff over the soil surface and groundwater recharge, where water percolates down through the surface layers of soil to the groundwater zone beneath. Let’s take a look at each of these in turn, and some of the ways we can slow this loss.
1. Inhibit Evaporation
The longer moisture sits at the soil surface, the more opportunity there is for it to evaporate or be wicked away by the wind. You want water to infiltrate the ground – fast.
Gradual improvements to soil structure made with regular additions of organic matter will help to open up heavier soils so that water can more readily drain into it. Shading the soil surface with a thick mulch of the same – compost, leaf mould, grass clippings, straw etc – will slow down evaporation still further.
Complementary to traditional horizontal mulches are vertical mulches. Vertical mulches use columns of material to direct the flow of water straight down into the soil where it’s needed. Vertical mulches can be very useful around fruit bushes or within beds filled with larger vegetables such as squash, tomatoes and climbing beans. To make one, drill out soil with an auger then fill the void with loose organic materials. Old stems and flower stalks, arranged vertically, will help to keep the hole open while channelling moisture down to the bottom of the column and into the root zone. Buried pots and pierced bottles used for indirect watering work on the same principle.
2. Reduce Transpiration
Every plant loses water as it photosynthesises, though xerophytes (plants adapted to dry conditions) are notoriously good at keeping this loss to a minimum. Suspending shade cloth over low-growing crops can help them keep their cool in hot weather. But this is only half the story. Wind can ruthlessly strip fleshy-leaved plants of their moisture, turning them from turgid to floppy in a matter of minutes.
Windbreaks are the solution to overcoming drying winds and can be permanent (e.g. hedges) or temporary (e.g. netting). Micro-sized relief from wind can be offered for delicate seedlings too. Plant into shallow depressions, build up miniature berms to the windward side, or stab tiny windbreaks of densely-packed fronds, stalks or pea sticks into the ground.
Don’t forget the mothering effect that taller, tougher plants such as sweet corn can have on more delicate darlings. Use tall crops to cast shade and fend off those wicked wicking winds. Equally valuable are sprawlers like squash that carpet the ground to keep it cool, hidden from the prying rays of summer sunshine.
3. Limit Runoff
It’s frustrating to witness water washing straight off the soil surface during a rainstorm. It’s downright heartbreaking after weeks of drought! Our strategy should be to trap as much of it in the soil as possible while collecting what we can for future use.
Planting into sunken garden beds or natural depressions in the ground is a great way to take advantage of the fact that water flows downhill and will inevitably pool in these areas. Another strategy is to develop a matrix of earth berms across growing areas, in effect creating a series of miniature reservoirs that hold the water in place so it has a chance to soak into the soil. Also known as ‘waffle gardens’, these typically grid-like designs are incredibly effective at minimising wastage of irrigation water.
4. Store Water in the Soil
Very free-draining soils such as those with a high sand content present the opposite problem to heavy clayey soils. While moisture quickly moves from the surface to the root zone, it won’t hang about there either! The solution is simple – incorporate lots of organic matter to improve soil structure and its water-holding capacity. It’s not an innovative idea, but it works.
Overwatering can inundate the ground with moisture so that the excess moves deeper down, below the reach of most roots. Clearly anything beyond the root zone can’t be used by your plants and for most vegetables that means a depth of around 45cm (18in). Check the moisture content of your soil regularly by digging an inspection hole. If it’s cool, dark and damp to a good depth, ease off the irrigation.
Be guided by what works in your area. Think about wind direction, watering technique and crop choice and always think of water as the privilege it is. Check out our other guides to watering wisely and conserving soil moisture and share your water-saving tips below.