When Should Plants Be Watered? Simple, When They Need Water. But The Art Of Watering Defeats Many Gardeners, Leading To Poor Yields/Plant Death. And Professional Growers Leave Watering To Most Experienced Person Employed.
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Watering looks easy. Just use a can or hose and add water to the soil around the plants. Simple ehhh?
If only it were. Watering is actually the hardest skill to master. And it is the one that attracts so many myths that have been passed down for generations, BUT aren’t true! How do I know? Well decades as a commercial grower where being able to feed my family depended on my ability to water my crops effectively is part of the reason.
Watering is not a job for kids! Read why below.
Watering Can Be A Chore
Each year we grew 10,000 tomato plants, several thousand pepper, chilli and cue plants, unto 100,000 celery and half a million lettuce. Many of these were in greenhouses or polytunnels but many of the lettuce and celery were outside as were my outdoor veg crops such as100,000 leeks etc. The reason I explain this is because every one of these crops needs different watering. Celery needs loads of water, even if it has rained it needs more. After. all it is a marsh plant and revels in being grown in wet but well drained soils. Toms, cues, peppers and chilli all need watering every day if in greenhouses or polytunnels but require different amounts depending on species, size etc. Lettuce prefers to have coolish roots .. though that is not always possible … but can be watered less frequently if watered correctly. Outside we did them every few weeks, depending on the weather, but ensured they had water once they were starting to heart up. It is a bit like watering potatoes once the tubers start to swell. This is when farmers tend to water as it gives the best response to limited water.
To learn more about watering read there rest of this article where I give both broad brush and detailed info.
The Golden Rule: Emergency Watering
If a plant is wilting severely and the soil is bone dry, it is on the point of collapse. Water it immediately, regardless of the time of day.
The ‘Sun Scorch‘ Myth: There is a common belief that watering in midday sun burns wet leaves because water droplets act like magnifying glasses. This is untrue for almost all plants (only a few very hairy-leaved varieties are at risk). Leaving a plant to suffer severe drought stress is far more damaging than watering it in the sun. Sadly a lot of people still argue that the raindrops magnify sunshine and burns leaves .. and I bet someone will tell me it is true, despite the science proving it not to be true! Many will say the “Old Boys” say it is true. Believe this old boy, it isn’t. If it were then commercial growers would never use overhead irrigation on crops such as lettuce … and Ik water half a million a year with overhead irrigation!
Time of Day: Morning vs. Evening
For routine watering of healthy plants, early morning is the most effective time .. despite other claims. Let me explain why … but don’t worry if you prefer evening watering, it can be done. But you lose some of the benefits that morning watering offer .. especially in hot weather.
Timing
Advantages
Disadvantages
Early Morning(Best Option)
* Less water is lost to evaporation than watering at noon! * Leaves dry quickly as the day warms up, stopping fungal spores from settling. Unlike evening watering. * Matches the plant’s natural daytime growth cycle.
* Requires getting out to the plot or garden early before the sun gets too hot.
Evening
* Water does not evaporate in the dark. * Gives the soil all night to soak up the moisture.
* Leaves stay damp all night, creating the perfect conditions for powery mildew and grey mould (botrytis). * Creates a damp environment that attracts slugs and snails.
Watering Style: Daily Sprinkling vs. Intermittent Deep Soaking
How you apply water alters how a plant’s roots grow.
Deep, Infrequent Soaking (Best for most crops)
Method: Give the ground a thorough drenching (around 4 to 5 gallons per square yard, or 24 litres per square metre) once or twice a week.
Benefit: Water sinks deep into the soil. This forces the plant’s roots to grow downwards to find moisture, making them much tougher and more resilient during a dry spell.
Suitable for: Established fruit trees and bushes, brassicas (cabbages, cauliflowers), root vegetables, and most open-ground crops.
But don’t forget, many crops don’t need watering once they are sown or planted. For example we grew 100,000 leeks a year and never irrigated once they were established. Most years we just transplanted without water. Only of it were very very hot and dry did we run the mobile rain gun over them once planted. This was to settle them in and ensure they had plenty of moisture around the roots to initiate growth. It is a bit like giving them a touch of water once they are dibbed in.
Ditto our brassicas. You can’t use a watering can when you transplant 20-50,000 Brussels or cabbage. So they went in deep and we expected them to drop for a day or two before they got going. The secret was to pull field grown plants at the right stage and plant deep into soil that had some moisture deep down. A few days after transplanting the “cocks” .. the centre of the plant .. would perk up and start growing. Plants can tolerate far more of this sort of treatment than many gardeners understand. BUT an experienced commercial grower knows when enough is enough and interventions is needed.
When I lived in Bedfordshire many local farmers grow Brussels. hundreds of acres of them. They were rarely irrigated. Mainly because they had no water source in the fields.
Frequent, Shallow Watering
Method: A light, daily sprinkle that only wets the top centimetre or two of soil.
Risk: This encourages roots to stay right at the surface. If you miss a single day in hot weather, the surface soil bakes and the shallow roots die.
Suitable for: Seedbeds, newly pricked-out seedlings, and quick-growing surface crops like salad leaves and radishes.
But the sooner you wean the plants on to less frequent watering the better.
Where and What You Are Growing
Watering needs change completely based on the location and the specific crop.
Greenhouses and Polytunnels
Plants under cover are 100% dependent on you because no rain ever reaches them.
They need checking every day. Don’t rely on moisture meters. Read the plant. It will show you when it needs water. Slight wilting comes after the plant starts to lose its obvious vitality. Green fingered growers recognise not long before those with less experience. Regular deep watering helps prevent a build-up of natural salts in the surface compost that can occur in some situations. Morning watering also helps keep the air cool and humid during heatwaves.
The latter is important in greenhouses and polytunnels. We often advise wetting the paths down .. a good watering does this naturally.
Pots, Troughs, and Grow-bags
Containers hold very little compost, meaning they dry out rapidly. Terracotta pots dry out even faster than plastic because water evaporates through the clay walls.
In the height of summer, container plants usually need watering twice a day (morning and late afternoon).
Plan your crops in containers carefully. Use the biggest pots you can as they hold more moisture. The bigger the better. And keep the pots out of the sun. Wrap some card around them to keep the direct sun off the pot. Put some mulch on the top as well.
Soil and Crop Considerations
Soil Type: Light, sandy soils drain instantly and need frequent, smaller waterings. Heavy clay soils hold water well but absorb it very slowly; water them gently so it sinks in rather than running off the surface.
Thirsty Crops: Tomatoes, marrows, courgettes, cucumbers, and sweetcorn need a steady, uninterrupted supply of water, especially when flowering and setting fruit. Erratic, up-and-down watering causes tomatoes to split or develop blossom end rot (where the bottoms of the fruit turn black and leathery due to poor calcium uptake).
Watering From Below Or Above?
I am writing a longer post on this topic. But in all the millions of plants I have grown I have never watered from below. It has always been drip irrigation for toms, pepper and chilli crops. Either drip or overhead for cues .. they like it humid. And all my millions of lettuce and other salads have been watered by overhead irrigation. If it did any harm professional growers wouldn’t do it!
