Updated/Fact-Chacked on June 27, 2023 by Gareth James
If you are starting out with gardening, it’s difficult to know how often you should water your plants, especially when websites give you different answers. This guide was written to answer all your outdoor plant watering questions after speaking to many gardening experts and extensively researching the facts.
Though people think of the UK as a wet place, we actually get less rain than many other countries. London even has less rainfall that Sydney. We also get the ‘wrong type of rain‘; heavy winter downpours followed by long spells of drought. At the time of writing in mid-May, we haven’t had rain for weeks.
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When is the best time to water plants?
The best time to water outdoor plants is in the morning before the sun is too hot. As soon as temperatures heat up, water will evaporate from the soil surface without being able to penetrate down to the plant’s roots.
The evening is also a good time to water plants but can help slugs and snails travel more effectively. If you have mature plants that slugs don’t like, you will be fine – don’t water hostas at night.
How often should you water outdoor plants in the UK?
Each plant will have its own watering requirements, but the general rule is to give them a good soak at the base every few days rather than a light sprinkle every day.
Plants in pots and containers will require daily watering in warm weather to stop them from drying out. Plants in pots cannot send roots out far to find water.
How much water do you use?
You must give your plants enough water to seep down to the root level. Try giving them a sprinkle, then digging the topsoil away and seeing how far the water has travelled – at 2cm deep, the soil will be bone dry. You need to give them a really good soak at the base of the plant, not a sprinkle over the whole plant. Plants will need more water in hot weather as they transpire more.
Signs that your plants are under watered
If your plants start to droop, it’s a sure sign they need water. The sunflower image below is a good example of a plant’s appearance if under watered.
A plant’s foliage can also totally change colour if it does not get enough water, usually a lot darker. Below is a picture of one of my matchstick chrysanthemums in a pot that completely dried out when I was away. The foliage has gone very dark but still seems to be alive; I’m trying to bring it back to life.
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10 watering tips for outdoor plants
1. Containers will need more water and attention
Containers restrict a plant’s root system; they have less space to move and find moisture. If you are planting moisture-loving plants in containers, look at creating water-retentive soil by adding coir or water-retaining capsules. These will need monitoring by someone if you are planning to go on holiday.
2. Water the actual roots and not the plant’s foliage.
Here’s a great video by Alan Titmarsh which shows how to water a plant efficiently. He talks about creating a small well around the plant to help water drain down to the roots – 1 inch of water will travel 6 inches deep.
https://www.youtube.com/watch?v=R8n4hG7NXbY (will open in a new tab, video is blocked from embedding)
3. Soak the roots at intervals
Plants need their roots soaking at intervals rather than a quick sprinkle every day.
4. Use mulch around your plants
Applying mulch around your plants will aid water retention; check out our complete guide to mulch.
If you want to buy mulch, look at Miracle Grow’s Mulch, it’s very fibrous and can also be used in winter to protect roots from frost.
5. Don’t wet the plant’s leaves too much
If the leaves are left damp for a long period, it can promote disease.
6. Check your plants daily
Become obsessive like me. Having my morning latte and strolling around my garden at 6.30 am on a beautiful morning is a pleasure. Look out for any wilting or signs of damage – this is more important if you are trying to establish a new border.
7. Use an Olla irrigation system
Plants that require a lot of water, like tomatoes, can be watered by burying a clay pot in the soil next to them. Once you fill-up the pot, it will slowly seep out into the surrounding soil.
Check out Epic Gardening’s video on Olla irrigation systems.
I’ve just bought a batch of terracotta self-watering spikes off Amazon for my week away this summer. These clay spikes are perfect for containers.
8. Use a drip irrigation system
If you are growing thirsty plants over a large area, consider an automated irrigation system that will drop water into the required areas. These can be timed and hooked up to water butts.
The top-rated system is the CROSOFMI Watering Timer. But that’s just the timer; you have to buy a hose kit with drip irrigation adapters.
9. Use water-retaining granules in pots and containers
Granules can be added to container pots to help retain water; these are good if you have a lot of hanging baskets. Find biodegradable ones, like Swell gel and Chempak Supergel.
10. Invest in a rain butt
Rain butts are more economical with water, while rainwater is much better for your plants having the right PH levels.
11. Don’t forget your shrubs and trees
Though they have large root systems, they would appreciate extra help during dry spells.
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How to be more economical with Water
Investing in a rain butt is a great way to reduce your water consumption. Rain butts capture rainfall from roofs and funnel it down external drainpipes into the butt, instead of going down the drain. A water butt will also save you money if you install a water meter. See our guide to some great rain butts available.
Knowing exactly how much water your plants need will help you be more economical without having to water randomly. Vegetables need more water than perennials, but annual flowers require regular watering, especially in spring.
Your soil’s ability to retain water can also be improved by adding organic matter, such as general garden compost or worm compost, which will feed your plants. If your soil is very bad, consider adding colloidal humus compost, not to be confused with edible hummus!
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John Green is a 46-year-old graphic designer living in Durham. John is RHS level 3 certified and owns an allotment in Durham.