Tuesday 21 August 2018

Wise to water, water, everywhere...

Now that summer is heating up, how often should you water? Gerry Daly advises

Plants of all kinds need water to grow and to thrive — especially in hot, dry weather
Plants of all kinds need water to grow and to thrive — especially in hot, dry weather

summer has arrived, and we're having unusually long, hot days. Do you need to water your garden? Plants of all kinds need water to grow and to thrive. Water, after all, is part of the fundamental process of photosynthesis that combines water and carbon dioxide to make sugars and oxygen, both vital not just for plants but for almost all life on Earth.

Growing outdoors, plants depend on natural rainfall, but artificial watering can be necessary if natural rainfall has been inadequate, or if a plant's root system is not properly established. Seedlings, young plants, especially vegetables, and plants growing in shallow or dry soil, are most likely to be at risk. Pot plants are completely dependent on your watering them.

The Irish climate is very favourable for plant growth as it delivers reliable rainfall in every month of the year. Normal summer rainfall is at least 50mm a month. This is so even in the areas of least rainfall near the east coast around the Dublin area. This amount of rainfall closely matches plant requirements. 25mm of rain is equivalent to almost 25 litres per sqm of water. If there has been no rain for a week, plants need about 12.5 litres per sqm, perhaps even more if the weather has been very hot. Established plants with deep roots can keep going in a spell of drought by drawing up water from deep in the soil, but young plants and those with shallow roots may need intervention when they come under stress due to water shortage.

The water needs of plants vary considerably as they have adapted to their natural conditions. In regions and habitats where water is plentiful, plants don't need to evolve water-saving adaptations. Plants with large leaves, such as gunnera and skunk cabbage, are usually an indicator of having a plentiful steady supply of water. Ferns are an important exception as they have evolved large leaves to cope with lower light levels. Having small leaves, leaves rolled lengthways, hairy or woolly leaves or those with a coating of wax, lending blue or greyish colour to foliage, are all ways that plants may evolve to avoid moisture loss. Some plants called succulents have thickened leaves or stems that store moisture.

Water new plants when you plant them, including vegetables, flowers of all kinds and trees and shrubs. Vegetables will need water a few days to a week later and repeated as necessary but still most will not get any extra water after establishment except in a dry spell.

Raised beds often need more water than others. Perennial flowers, shrubs and trees might need watering several times after planting until new shoots are produced, a good sign that the plant has settled in properly.

Look out for wilting, which is a sign of drought when the cells contract after moisture loss. More long-term survival strategies include leaf loss, reduced leaf size and volume, and the creation of a thickened wax layer that leads to a hardened look.

Long-term moisture shortage can occur in dry sandy soil and may be due to the roots of competing plants, trees being the most aggressive of plant competitors.

Water deeply and allow enough time for an adequate amount of water to be delivered, letting it soak down where it will be effective. Heavy, short bursts are no good as the water just runs off. When watering larger plants, make a little dam of soil around them and fill it inside with water. Re-fill it if the water disappears quickly. Shallow rooting shrubs such as rhododendron often need this attention, even as established plants. Wall shrubs, too are very drought-prone because of the rain-shadowing effects of the wall.

Timely watering is essential for plants in pots, whether in the house, greenhouse or outdoors as the amount of rainfall that falls into pots is negligible. However, the use of fewer bigger pots can reduce water need, as can training plants to adapt, such as pots or baskets, by not watering each day. Lawns need never be watered in this climate as rainfall is reliable enough to rescue them even after an exceptional drought.

IN THE NAME OF THE ROSE: It's possibly the most loved of any flower, celebrated in art, politics and religion, the rose will be the subject of Assumpta Broomfield's upcoming talk, 'Scenting and Searching the Rose' with anecdotes about some of the plant's explorers and collectors. At Woodville Walled Garden in Kilchrest, Loughrea, followed by a tour of their own famous roses. Next Saturday at 2pm €10; woodvillewalledgarden.com

PLANT IT: Looking its best at the moment, broom is a native wild species that is quite widely grown in gardens for its yellow flowers, or red flowers in some forms. It is a fast grower in well-drained soil, making a tall bush to over 2m, though the garden forms are smaller. 'Killiney Red' and 'Hollandia' are red and pink varieties respectively. You'll find it in garden stores nationwide.

GO SEE IT: Limerick has a long history of gardening throughout the city and county. Now, growing enthusiasts can enjoy talks from experts such as Des Kingston winner of Super Garden 2017 and broadcaster Peter Donegan, as well as show plant and food stalls and demos at the first Limerick Garden Festival next Sunday at the Milk Market. More details: limerickgardenfestival.com

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