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Above and Below Ground
 Plants that must cope with parched soil need to grab every bit of water going, and hold on to it and roots and stems have a vital part to play
- Thick fleshy roots (Agapanthus, hemerocallis, kniphofia) capture and hold water
- Long tap roots (cordylines, acanthus, poppies) reach deep into the soil in search of water long after the surface layers have dried out
- Alpine plants and those on gravely, shallow soils (lavender, cistus) have extremely long, fine roots that extend over a wider area taking up as much water as they can get to.
- Bulbs take up water during damp winters and spring and then, becoming dormant, store moisture through out the dry summer months.
- Swollen stems store water for dry periods, cacti and the bilboa trees of East Africa are fascinating instances of water storage in stems.
Life Cycles
 Some plants have modified by concentrating all their growth in the most favourable season. The plants germinate, grow, flower and set seed all before the drought and heat return, surviving inhospitable conditions as seeds or dormant underground.
Short, rapid life-cycles are a feature of the many desert wildflowers found in the Texas hill country and Western Australia. This 'desert' blooming is a spectacular and wonderful event each spring when warmer temperatures coincide with moisture.
Bulbs from many areas of the Mediterranean and Turkey flower during the moist winter and early spring, and then, after a short 'life-span' disappear beneath the surface, re-emerging when conditions are again suited to growth again.
Plants under stress commonly defoliate, shedding their leaves during dry inhospitable weather. In a dry year leaf-fall on deciduous trees comes early as plants strive to conserve energy. Recurring defoliation is a special adaption of the ocotillo (Fouquiera sp.) of the American southwest; it develops leaves after periods of rain, holding them for only a few weeks before becoming bare and twiggy again.
Armour
The spines and thorns of many arid dwellers are protection from browsing animals in search of food and moisture. Cacti well-known examples of this, but native matagouri (Discaria toumatou) spines deter browsing.
Other plants are distasteful, full of pungent oils, that deter would-be diners.
Survivors All
Plants are survivors, modifying in myriad ways and adopting a number of strategies to ensure survival from one season to next. Understanding these ingenious strategies helps gardeners handle harsh climates and chose plants that will flourish.
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 More Garden Botany
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Alliums and other bulbs flower before summer droughts set in |
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Low rainfall forces plants to be water efficient
Tap rooted-lupins are common wildflowers in dry Central Otago summers
Cacti and Desert Plants
 Deserts are found where there is not enough water for most plants to grow. Deserts and arid areas cover about a third of the world's surface.
The driest desert is the Sahara Desert in North Africa, with some areas getting less than 1mm of rain each year, and Antarctica is the coldest. The Atacama Desert in Chile is also very dry and rain can fall only every few years. There are desert areas on all the major continents. In New Zealand, we have several very regions that are very dry, especially in summer.
Desert plants show us that nature has worked out some clever strategies and that there's a reason that cacti look so, well weird, compared to other plants.
How Desert Plants Save Water
Desert plants have to be their own water tanks and collect as much water as possible from storms and rain showers.
Cacti and succulent plants often have swollen stems and no leaves, and this reduces water loss from transpiration (to find out about transpiration see our rainforest project). We've all seen ice plants at the beach, with fat grey-green spikes for leaves. If you bruise them, those leaves are full of moisture, moisture that they are storing.
Some plants are almost elastic, expanding to hold water when rain falls and then using it slowly over a long period. For example, cacti with ribbed stems can expand after rain to hold as much water as possible.
Some plants catch water in their saucer-shaped leaves, giving them a chance to absorb after the rain shower has passed. Sedums grow in rosettes that catch the water, which they can then soak up.
Reaching Water
Some cacti have hugely long roots that reach far down into the soil in search of precious moisture. Mesquite bushes that grow in North America have roots that reach down 10 metres (33 feet) and other plants can go even deeper. |
Fierce spines and fleshy swollen 'leaves' on the Prickly Pear, Opuntia robusta
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