News from Cold Ash Horticultural Society

For the list of 2012 meetings and events go here

Drought Gardening and Global Warming                                    


In July 2010, Kelvin Mason, a lecturer at Sparsholt Agricultural College, gave a talk to Cold Ash Horticultural Society and reviewed the impact that climate change will have on gardening  in England. He provided some practical suggestions on how to make maximum use of water resources and reviewed those attractive plants for the ornamental garden that can cope with drought.


The message is clear that climate change is happening with 98% of scientists agreeing that this is associated with the continual global rise in atmospheric CO2 levels. A detailed review of the impacts of climate change on gardening in the UK can be found at: Gardening in the Global Greenhouse, a joint report from the RHS, National Trust and UK Climate Impacts Programme
( ). This 2002 report points out proof the UK is getting warmer is now quite evident, with over 400 productive vineyards around the country and parts of the South of England becoming ideal terrain for champagne production. Summers are getting hotter, winters warmer and the growing season becoming longer. There will be much more of a Mediterranean feel to the climate: “Hot dry summers, warm, wet winters with westerly winds” as my geography teacher used to say. However, although this represents the trend in climate change, we need to be prepared to cope with much more extreme changes in weather, with greater risks of drought some years, severe gales, wetter winters and, as last year, sometimes very cold winters. The report warns that with a warmer climate will come threats from new pests and diseases: mildews, oak wilt and insects, such as the Lilly beetle. Such pests can now survive over winter and more readily spread across the country.


Plants are 85 – 90% water – cucumbers and tomatoes as high as 95% – so with water shortage comes stress, increased risk of disease and poor production. Getting the basics right is the key and Kelvin recommended introducing organic matter into the soil as most beneficial since it helps the soil retain water, provides nutrients and essential minerals such as potash, iron, manganese and phosphates. Organic matter can take the form of manure (the best is well-rotted horse manure), compost, leaf mould or green manure (crops such as mustard, rye grass or clover can be dug in once grown), the latter especially valuable if it is a nitrogen fixation crop such as clover.  The clear message was feed your soil and not the plants and the good news is that digging in is  best but not essential, as you can layer composts onto the soil and leave the earthworms to do the job of ‘digging it in’.


With regard to watering, what is most important is its penetration to the roots. Frequent watering does little good if it is not available to the plants. Five gallons of water per square yard will only penetrate to one inch of depth. The message here is, thorough watering at weekly intervals is better than frequent light watering. However, don’t water seedlings too early or too much as they need to be encouraged to develop good root systems that can seek out scarce water supplies. Trickle or drip irrigation systems are advantageous when they deliver water to the root system.


There are many ways of using recycled water but clearly the best system is to collect rain water in covered water butts. The covers prevent leaves and debris falling in and limit algal growth so stopping the water becoming stagnant. Rain water is clean, slightly acid and free of pests and diseases and can be used for most plants. The exception is seed trays and newly-planted seedlings, where tap water is advantageous. The average British household uses 28,000 gallons of water each year and ‘grey water’ from showers and baths, washing up water and even washing machine water, can be used for watering the garden provided it does not contain a lot of grease or strong detergents. Dishwasher water is problematic, however, because waste water from first cycle may contain strong detergent and bleach.  ‘Black water’ from toilets is best avoided, although human urine can be collected and used as an excellent activator for compost and good plant food.


Kelvin pointed out that lawns need vast amount of water to keep them green throughout the year so he suggested leaving them unwatered over the summer for they are hardy and quickly recover their green condition come September. Many vegetable crops, especially brassicas can survive in the vegetable garden without the need for watering. However, watering cucumbers and tomatoes is absolutely essential. When it comes to potatoes the rule is only water early varieties but not main crops.


In the ornamental garden drought-hardy plants to consider growing are: 

Achillea species such as cyserinchium or ptarmica (‘The Pearl’)

Agapanthus varieties

Allium family

Berberis (choose waxy leaved varieties),

Cistus ‘silver pink’ (rock rose),

Corokia cotoneaster (wire bush plant),

Cotoneaster dammeri,

Crocosmia or Monbretia

Cytisus prostratus (Prostrate broom)

Echinops (Globe thistle)

Genista (Broom family),

Gypsophila family

Penstomen pinifolius

Phlomis fruticosa

Rhus sumach (Stag’s horn sumach),

Ruscus aculeatus (Butcher’s Broom)

Salvia officianalis (Sage)

Sedum maximum

Sempervivum family


Fred Davison

Cold Ash Horticultural Society