When is the Best Time to Water Plants?

Whether learning by experience or by reading up, you’ll soon come to realise that - for the most part - there are no hard and fast rules for gardening. This applies to irrigation as well. Sure, there are some principles to keep in mind or to apply at different times of the year. But ultimately it’s about adaptability and being flexible. 

1 - Watering the Garden

Maybe the first factor we should consider when it comes to the best watering time is, where the plants are going to be situated: outdoors in the garden? in a greenhouse? a polytunnel? in container? or indoors on a windowsill? Each of these is a different environment and the plant will have to adapt (as will you) to that environment.

Of course, plants outdoors (whether in the garden or in raised beds) will not be relying entirely on you for their watering needs. There may be long periods of drought at times (and this might well be something we’re going to have to live with more and more over the coming decades), but there will also be plenty of days when plants will be naturally irrigated via rainfall. At such times, you can give your watering can a break. Keep an eye on the weather forecast and you can save yourself some work.

Rainwater is regarded as the ideal form of watering by many gardeners. Indeed, if plants could talk themselves they would likely confirm this for us. Rainwater is naturally on the slight side of acidic, which is something that plants really thrive on. It contains nitrates and is free of chemicals like chlorine which are added to our water supply.

Take a look around at nearby foliage or shrubbery after the next heavy rainfall and see for yourself. Plants will look greener and more vital. The rain also tends to give soil a good healthy soak, draining or diluting sodium buildup.

Outdoor plants shouldn’t be watered every day. Depending on conditions (e.g. not overly dry, drought-like weather), irrigation can be spaced out and done every 2 weeks or so. Which should free you up for other important activities! Andrew, one of the bosses here at Quickcrop is a firm believer in treating outdoor plants ‘mean’ for their own benefit: when you don’t irrigate too often, the roots will work harder to find moisture in the soil, which makes for stronger crops.

However while this is general advice, some crops may need more regular watering. Certain plants - such as spinach, Pak Choi and radish - are prone to bolting in warm weather or during the summer months, and keeping the soil moist and well watered can help stave this off.

2 - Watering in a Greenhouse or Polytunnel

On the other hand, plants in a greenhouse will need much more attention from you. Temperatures can rise pretty high in a greenhouse (and in a polytunnel for that matter). Indeed if real life gets in the way of your gardening duties, things can escalate to the point where plants suffer from heat shock or wilting.

Irrigation is by no means your only way of preventing this (ventilation and cooling also play important roles), but it is an important one. So is timing. Moisture can evaporate very fast in this enclosed environment, with watering very early in the morning being your best bet in summer.

Setting up a drip irrigation system can provide a steady, measured supply of water directly to the soil. Drip irrigation comes highly recommended. It’s something of a gamechanger and can save you untold amounts of time and decision-making. 

3 - Watering Plants in Containers

Plants confined to containers - such as pots or hanging baskets - will need more regular watering as the soil dries out faster. Some key principles to bear in mind:

• Water deeply, until you see water draining from the bottom of the pot.
• Insert your finger 2-5 cm into the potting mix; if it's dry at this depth then it's probably time to water.
• A good quality potting mix will retain moisture more effectively.
• Adding vermiculite to potting mix will enhance water retention.
• The smaller the container the more regular your watering regime will need to be.

The above does not apply to succulents or other drought tolerant plants typcially grown in containers.

Should I Water in the Morning or Evening?

Some common advice you will hear about the best time to water your plants is to do so in the morning or the evening. It stands to reason. Irrigating early in the day when the sun is not at its strongest gives your plants time to absorb moisture.

In the evening a similar principle applies, although some gardeners avoid this as it can lead to standing water on the plants. This is particularly a concern if you live in a humid area: moist plants overnight could potentially cause fungal or mildew problems.

Your mileage on this may vary though; in reality they’ll often be just fine. Late-evening irrigation also means that the moisture can soak deep into the soil without having to worry about the midday sun drying things out.

Observe Your Plants, Water When Needed.

With outdoor plants, a quick and simple soil test can tell you whether irrigation is needed, Stick a trowel in the soil to check for dryness. You can use your finger as well by pushing it into the soil until it’s halfway buried.

If the soil is moist, watering will not be necessary. If the finger comes out clean and dry, insert it further again. If it’s still dry, it’s time to fetch your watering can. 

If you garden for long enough you will eventually get a feel for how a pot should weigh when it’s dry, as opposed to when it has healthy levels of moisture. This kind of ‘earned knowledge’ extends to sensible irrigation in general. When you’re a relative beginner it can feel a bit confusing when you see people extol the virtues and importance of irrigation on the one hand, while cautioning against the scourge of overwatering on the other. Which is it?!

With experience, a lot of this stuff will become second nature, even if it takes a few fallen soldiers to get there. You will also get a feel for how often individual plants need to be watered: this one is needy, but that one over there is made of steel.

Watering Deeply

If watering is to be a relatively infrequent occurrence (such as in the case of outdoor plants), then it’s all the more important to ensure that you’re watering deeply. With 'deep watering' you want the moisture to be seeping around 8 inches deep into the soil. It encourages deep rooting, with plants becoming stronger and more self-reliant. Again, you can measure effectiveness here by using your hand or finger to test the soil.