In Excessively Hot Weather Plants & Gardeners Can Wilt.  Gardens, Conservatories, Greenhouses And Tunnels See Temperatures Soar, Pots Dry Out Very Quickly And Plants Can Soon Collapse. So What’s The Answer To Soaring Temperatures And Wilting Plants? In This Article I’m Going To Give My Answers Based On My Practical Experience, Initially As A Market Gardener And Later As An Amateur Gardener. 

Here are my top Hot Weather Plant Care Tips

In the Victorian garden watering was overseen by the most experienced gardener. Not a reward for time served, but because they had more knowledge and experience than the apprentices. 

Water Infrequently for Best Effect

Watering little and often means the water barely penetrates the surface and the roots keep near the top to find what little there is. But if you give the ground, and the plants, a really good drenching the water goes down and the roots follow. A reservoir of water is retained by the soil and the plants can benefit for days. The works for crops that have a free root run in the soil and are able to send their roots deep. 

Pots are another thing altogether. They have limited capacity so can’t hold as much water. They will need watering more often and will often suffer less if stood in a tray to catch water than runs through the pot. And plants such as tomatoes, cucumbers, melons and similar are going to need watering everyday if in a greenhouse. Even with a good root run they do much better if watered every day.

In case you wondered when irrigation was first used here’s a post on wikipedia. The practice goes way back into history.

Retaining Water In Soils and Pots

A soil with plenty of organic matter is always going to retain more moisture than one without. So adding compost, well rotted animal manures etc will help the soil retain moisture. It will also aid drainage when the rains return! 

In pots you could add water retaining gels. To an extent they work. But remember that every handful of gel displaces a similar amount of compost. Add too much and there is less growing medium for the plants. That means fewer nutrients to grow the plant.

When To Water Your Plants

Water when it is hot and windy and a lot of your water will evaporate or blow away. It’s far better to water early in the morning or late evening, when the sun is less powerful and the wind is likely to be less blowy.  

Commercially I used a mobile raingun to irrigate my outdoor lettuce and we always watered overnight for the above reasons. Imagine a huge sprinkler that sprayed water 20-30 feet to either side as it was mechanically and slowly pulled across a field full of lettuce. When it reached the far side of the field it turned itself off and tens of thousands of lettuce had been irrigated with water that went at least a foot into the soils. 

In my greenhouses I used overhead sprinklers, suspended from the steel framework of the greenhouse to produce a fine rain of water droplets that would fall evenly on my crop for 20-30 minutes every few days. Others used soil mounted sprinklers to do much the same. I preferred overhead sprinklers as they were permanent and didn’t get in the way when we were planting or harvesting.  

On an amateur basis sprinklers are available or just use a watering can. A good drench from a can can be just as effective. 

Drip irrigation for tomatoes - Hot Weather Plant Care
Drip irrigation for tomatoes

Crops such as tomatoes and cucumbers were watered with drip irrigation. It gives a steady drip of water and feed to the base of the plant at any time of day. Tomatoes I used to water at coffee time each morning and sometimes give them a second watering in late afternoon if they needed extra. And cues I would water twice a day to ensure their roots always had plenty of water. Cues need lots of water and can tolerate high humidity conditions that toms can’t survive. Too much humidity in a tomato house and blight is a possibility. I’ve never seen blight in a commercial greenhouse but that’s because commercial growers manage the humidity. 

Celery crops were watered using overhead irrigation and would be given around 30 minutes a time. When the crop is growing well it is so dense that it takes 10-15 minutes for the water to penetrate the crop. Sometimes I’d give them as much as an hour’s watering. We added nutrients to all the water given celery, toms, cues and peppers. 

In pots, or where the soil gets baked by the sun, many amateurs swear by putting a pot or bottle in the soil so they can add the water to it and get it right to the roots. It’s a good idea. 

Watering is Easier in Larger Plant Containers 

Plants need plenty of space for their roots. The more soil or compost they can root in the happier they normally are. More space means more moisture and feed. So plant in the biggest size pot you can. Better still plant in the ground if you can. Plants will send their roots deep into the soil if they can.

Mulching To Retain Moisture

Adding a mulch to the soil helps it retain moisture. But add the mulch to a moist soil, not a dry one, or the mulch will stop the moisture getting to the soil when you water or it rains.

Most organic materials can be used for mulching. As they break down they return nutrients to the soil.

The Water Burns Plants Myth

I’ve dealt with this elsewhere. But getting leaves wet doesn’t magnify the sun and burn the plants. The physics of this are impossible.  

If plants show signs of damage after watering in hot weather there are two regular culprits. Either the plant had wilted and had been damaged by wilting extreme cases they dry to a crisp! Or the water used was hot. Leave a hosepipe in the sun for very time and the water inside gets very hot. Make the leaves wet with this water and its doesnt burn  them, it boils them! 

Watering Lawns in Hot Weather

Grass rarely dies in the heat of a British summer. Sometimes it goes brown as it dries up. Sometimes it even loses some leaves. But the root persists and will regrow one it has moisture. Grass evolved to be able to do this. It grows from the bases whereas many plants grow from the top. 

But you can help your grass by not cutting it too short. In hot weather, raise the mower cutting height. It leaves the grass longer and that shades the soil surface which means it doesn’t dry out so quickly.  The grass survives much longer this way. 

If you want to water, do so by giving the grass a good drenching once rather than little and often. If hot summers persist, choosing a hardier grass variety might also help. Plus if you reduce cutting in May (No Mow May) and maybe even into June, the grass will not suffer nearly as much. 

Reducing Greenhouse & Polytunnel Temperatures

The temperature in a small growing house can soon soar when the sun comes out. So we need to drop the temperature and protect the plants.

However, in most cases, reducing light levels by obscuring the glass is rarely the answer.  Painting the glass with white paint, dilute whitewash or other materials also reduces light levels when the plants can do with the boost. 

Remember the objective isn’t to reduce light, its to reduce temperatures. 

The best way to reduce temperature in a greenhouse is ventilation. The second is by evaporation. 

Improved ventilation is often as easy as opening windows (vents) or doors. I say doors as one at each end gives a through-draft which helps a lot. Vents should be on both sides of the roof to enable a through-draught. And this works better if a side-vent or door is open to allow air in as the hot air goes out the top.

To stop birds, dogs, cats etc from getting into the structure you can add a piece of wire or plastic netting to the doors. It lets insects in and cats out! 

To further reduce the air flow try removing a few pieces of glass in the gable ends of a greenhouse. It really improves air flow. 

To further cool the house, wet the floors. A can of water over the soil or paved floor evaporates and reduces the temperature quite a lot. Repeat a few times a day if necessary.

Storing Rainwater for Hot Weather Plant Care

I’ve written a lot about collecting, moving and storing rainwater for later use in the garden and greenhouse.

There will be more on Hot Weather Plant Care in other article. But for now why not join my Facebook groups for up to date practical gardening tips?

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