When the warmer weather strikes, our gardens and outdoor spaces become a perfect oasis for rest and relaxation. But as nice as the hot weather might be, extreme conditions and record-breaking temperatures can wreak havoc on your plants.
There’s of course no question, that when it’s hot, plants will need watering, but knowing when’s the best time to do this can be tricky. Evening watering gives plenty of time for the water to penetrate the soil and for the plant to take it up, but there is a concern that leaves staying damp overnight will provide access to disease.
On the other hand, morning watering means leaves will dry out faster – but there is less opportunity for the water to penetrate the soil and for plants to take it up before the day gets hot. So what’s the answer?
All living things need water to allow chemical reactions in their cells that provide energy for growth. Plants also need water to carry nutrients from the soil to the growing cells. This water is drawn up to replace water lost through stomata – the breathing holes in leaves. These stomata are needed for gas exchange – carbon dioxide in, oxygen out – during photosynthesis. In high light levels, on sunny days, a lot of carbon dioxide is fixed to make sugars by photosynthesis. Loss of water is also important to cool plants on hot days.
If plants run short of water they shut down their stomata and photosynthesis stops and is replaced by photorespiration – a process that releases carbon dioxide. Desert plants get around this by breathing at night and storing carbon dioxide for release to photosynthesis during the day while the stomata are shut. But in our gardens, few plants are adapted to do that.
As the water shortage gets more severe plants will wilt – the beginning of cell collapse. Initially this is temporary wilting and the plant can recover rapidly when water is available. But further drying will cause permanent wilting, which results in the death of parts of the plant – or even all of it. Some plants survive drought by dying down below ground – this is the case with garden bulbs such as bluebells, daffodils, tulips and snowdrops. Others may shed their leaves or survive only as seeds.
Avoid full sun
What is generally agreed is that plants should not be watered while in full sun. The notion that wet leaves on sunny days cause scorch in plants was disproved nearly ten years ago. But there is no doubt that watering in full sun is not water efficient – as much of it will evaporate before entering the soil.
In the current hot breezy weather it is probably best to water in the early evening. This gives the plants enough time to dry out, but there is still the chance for overnight water uptake by the roots. And if you want to water in the morning then start very early – before the sun is shining.
When you water, the key thing is to ensure all layers of the soil in the root zone are wet. Regular light watering causes shallow rooting of plants and makes them less drought tolerant. So water plants thoroughly but occasionally – and don’t let the soil completely dry out because it becomes harder to wet at that stage.
You can water the soil rather than the plant, but take care not to cause the soil surface to form a hard pan. A bit of mulch (wood chips or compost) can protect the soil and keep moisture in – but beware of slugs.
Beware of over watering
Plants can have too much of a good thing – and while the surface might be dry, the soil 15-20cm down, might not be. Most plants will have a greater root depth so could well be pulling up water that you can’t see.
The best rule of thumb is if the plant is not wilting it probably has access to water. Some herbaceous plants will wilt in full sun to save moisture but will then rehydrate as the temperature cools later in the day (temporary wilting). My garden lupins are doing this on a daily cycle at present, but they are deep rooted and they do pick up in the evening.
You must keep containerised plants well watered. Water on to the soil and water in the evening. As with any other watering, water thoroughly and then not again until there is sign of need. Greenhouse tomatoes will probably need watering daily at present. And if you are growing carrots make sure the soil stays moist or you may end up with split roots.
Your lawn will probably be looking quite dry, but don’t worry too much about this – as grasses die back when dry but can regrow quite quickly when the rains return. One things to remember though, is to avoid excessive walking on a brown lawn or you will end up with bald patches – this is because the combination of drought and heavy wear are just too much for your lawn to handle.
So the message is clear, enjoy your garden in the heat, but remember that your plants are similar to us humans – they too enjoy a bit of shade and a nice drink.
This article was originally published on The Conversation. Read the original article.
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New allotmenteers often panic about getting enough water to their new baby plants. They have shared their nightmares about missing a single day, incase their neglect results in their first crop failure.
Having lived in the fens for all of my 50 odd years, I gently explain that the number of crops requiring water to be artificially provided are very few. Evidence can be seen where potatoes are watered in the dry summer weather, but you don't see the farmer out watering the newly sown wheat, or the growing young barley. Other root crops rarely need to be given additional fluid either.
It could be argued that weeds both help and hinder your crops. I have tried both methods. The strawberry fruit in both weed free but unmulched bed produced sufficient fruit and about equal to those I left in the long grass. Ok so the arguments could be that there may be different weight comparisons, but where some of the fruit were stolen (and hopefully enjoyed), it's not possible to make accurate comparisons. Perhaps this is a possible future experinments for my nephews to do.
I was heartened that when walking over the allotment in the very early morning, the long grass provided a source of moisture for the strawberry plants below (aswell as washing my feet). Would that moisture provide the strawberry plants with enough moisture? Did the grasses transpiration steal the water from the surrounding strawberry plants. Either way both survived and the strawberry crop was reasonably plentiful without any extra watering from me.
From being a child, I was encouraged to garden by my Uncle Malcolm, and I recall him telling me about the importance of watering around the plant stem and not on the leaves, for both root absorption and for the avoidance of leaf scorch.
Ensuring your plants have a good start to life and understanding each plant's needs and dislikes helps to prepare for their ability to grow and successfully fruit. Again the article touches on the development of roots being shallow when frequent light watering is given. Plant them and let them get on with it after a good initial soaking in.
Overwatering can cause as much plant damage as the underwatering which I have founfd out to my detrim ent recently. I have been trying unsuccessfully to grow Echium pinninana plants. These biennial plants I'd grown from seed did very well initially, then faded before reaching the second season and promised flower spike. The Seedlings had been kept frost free through a really cold winter, and then as I transplanted them out in their planting position, they looked content initially. Weeks later they wilted, and no amount of extra water could placate them. they faded, browned and died. I later discovered they prefer drier conditions, and also learned that I had an old ditch in their planting position, Definitely a case of too much water.
Next time I will read more of the plant's preferences and the history of my allotment site.