How much water do plants need to thrive year-round?
- By: Ashley Saunders
- May 2021
For plants to thrive they need water, the right soil and some care. And so you might wonder; how much water do plants need to thrive? But that’s only half the equation. You also need to pay attention to how often plants need water.
Due to climate change, population increase and our need to protect the environment, water is becoming an even more precious resource that requires proper management to ensure we all have plenty.
If you have questions about watering your plants or looking for gardening tips, we have the answers! So, just how much water do plants need?
When should I water my plants?
Let’s start with the most basic question of when to water plants. There is an ideal time to water plants each day. You should water in the morning, if possible. As the sun rises, the plants start to absorb and use the water.
Also by watering first thing, the foliage and soil surface is likely to stay drier for longer than if you watered in the evening, which discourages slugs, snails and mildew diseases.
As the sunlight heats the soil, plants start to transpire and start to draw water from the soil via their roots, stems and tiny pores on their leaves called stomata.
In some situations, evening watering is also fine. The cooler conditions could mean less water is lost to evaporation.
What you want to avoid is watering in the heat of the day as a large amount of the water will be lost through evaporation. So stick to watering your plants in the morning.
How often should I water plants?
You’ve probably been told a thousand times that you need to keep your plants well-watered! But what does this mean?! How do we know if a plant is getting enough water?
Sadly, there’s no general rule as different plants have their unique needs. For example, a mature shrub might need watering if there’s a particularly hot summer. A container with plants, on the other hand, that sits in direct sun will need watering daily.
It’s worth remembering, plants will absorb as much water as they can. So they will use more water if you keep topping the soil up with more water. It’s perfectly fine to let plants dry out a little between waterings.
Determining how much water do plants need
There are many factors involved when it comes to determining how much water your plants need.
Size, species and stage of growth
Larger plants with more leaves require higher amounts of water as they will evaporate water quicker and require greater amounts of nutrients to grow flowers and fruit.
Soil texture, structure and compaction
Plants can’t extract every drop of water from the soil and the type of soil also affect the amount of water they can extract. Clay soil, for example, can hold more water than a sandy one. However, plants can extract more water from sand than clay.
That said, sandy soil can feel dry even though there may be moisture still available to plant roots. So in general, sandy soils tend to need smaller amounts of more frequent watering than clay soil.
Where the plant is growing
A plant in a border has different needs than one planted in a container. For example, a large plant in a small pot requires more frequent watering than those in a border. As the border offers a larger surface area, the roots can draw more moisture than if they were confined in a pot.
The season and overall weather
Plants need less water in the winter versus the summer as the temperature is lower and there are fewer hours of sunshine. In hot, sunny and windy weather, plants tend to use more water.
So if you have a prolonged dry spell with little rain, then you’ll need to water more often as light showers will simply evaporate quickly without nourishing the plants or being absorbed into the soil.
How to correctly water plants
As plants only draw water through their roots, pour water over their leaves does little to help them develop. If you pull a mature plant from the ground, you’ll see a very complex set of roots, which enables it to draw water from the surrounding soil or compost.
Wet or humid foliage will encourage fungal problems and evaporation from the surfaces. So be mindful when watering plants that the water hits the soil. You might choose to water more thoroughly, but less often as this helps the water reach further to deeper roots.
Ideally, you’d water the garden before drought sets in as this will keep the soil moisture levels even and avoid the soil being continuously dry. That said, and equally important, the soil doesn’t always have to be overly wet because plants roots also need air to grow well.
If you’re planting in containers or restricted spaces, then you might want to water more frequently as this allow the plant to draw up sufficient water from the smaller area of soil.
If you suffer from poor drainage, then watering effectively can be difficult. You’ll either need to improve the drainage or choose plants that are appropriate for such conditions.
How much water should I apply?
The volume of water you should add will depend on the type of plant and how actively it’s growing. Of course, the soil and the whether are also important factors to consider.
Heavy clay soils will need less watering than light sandy or chalk soils. However, less water can be applied each time as the excess will drain away easily. Clay soils will need more water, less frequently as they hold more water within their structure.
It’s worth adding organic matter as this increases the water holding capacity of most soils while suppressing weeds.
As a general rule, when watering containers you can add about 10% of the container’s volume in each watering. If you have a 10-litre pot on your patio, then you could add 1-litre of water. Pour the water slowly and aim to keep the majority of it in the pot, not draining out the bottom.
Place a saucer under the pot to catch any excess water as this will also allow it to be re-absorbed. You can always test how much water your pot needs by gently lifting it after watering to see if it feels heavy, if not, then add a little more water. Over time, you’ll learn when to add more water.
Should your plants wilted between waterings, then you might want to water more often. Add water slowly and thoroughly so that it reaches the roots.
Which water should I use?
As free is best, use rainwater where possible. You may want to install a water butt to collect rainwater for later use.
Tap water, while fine can contain more minerals than many plants need.
You could use Grey water from your homes but this is best used in very dry spells.
What methods can we use to water plants?
There’s plenty of watering methods available from watering cans and hoses to sprinklers.
Let’s start with the most common, watering cans. They enable you to aim water at the plant’s stem while not dampening the foliage or a large area of surrounding soil. By targeting where the water lands, your plant’s root gets all the nutrients it needs while limiting the growth of weeds.
Self-watering pots and containers
These clever containers have an in-built reservoir that stores water away from the root zone but is connected by a capillary system. Plants draw water into the root zone as they need it while continuing to collect and store rainwater.
You can, of course, top them up by add water directly into the reservoir rather than the soil as this ensures that the compost and nutrients aren’t washed into the reservoir where it can make the water anaerobic and smelly.
Featuring pre-made holes, seep hoses deliver the right amount of water to established plants and plants in rows. They can be hidden beneath soil or mulch, along plant roots systems, reducing evaporation losses. They work best on heavy soil where the water spreads further sideways.
Automated irrigation systems
For larger gardens or fruit and veg plots where the water demand is greater, a drip or trickle irrigation system can make watering plants easier. Typically, these systems are operated on timers or rain sensors but still needs regular checking. They are ideal if you’re away on holiday.
As they need mains pressure to work, sprinklers have limited use in the garden. Plus in an hour they can use the same volume of water as a family of four people would normally use in two days.
How to be smart with your water usage
As water becomes more precious, there’s a need to reimagine your garden to deal with climate change and use less water. Part of this is learning more about each plant and what watering they require.
You can also reduce your water needs by improving your soil with organic matter such as mulch or manure so that it retains more moisture. Also, consider maximising how much rainwater you can collect and reuse as this lessens your need to draw water from other sources.
Another idea is to be picky about what you plant, where it’s located in your garden and the time of the year you plant it. Ideally, you should plan new plants between autumn and spring to allow them to grow before the weather becomes drier.