Hot Water And Plant Growth: Effects Of Pouring Hot Water On Plants

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Garden lore is full of interesting methods of treating and preventing diseases that no rational gardener would actually try at home. Even though treating plants with hot water sounds like it should be one of those crazy home remedies, it can actually be very effective when applied properly.

Hot Water and Plant Growth

You’ve probably heard a lot of really unusual home remedies for pests and plant diseases (I know I have!), but using hot water on plants is actually something that works quite effectively on certain pests and pathogens. Unlike various pesticides or home remedies, hot water baths for plants can be quite safe for the plant, environment and gardener alike, provided you’re careful how you apply the water.

Before we get started in all this hocus-pocus, it’s important to note the hot water effects on plant growth. When you add water that’s too hot to plants, you’ll end up killing them – there’s no two ways about it. The same boiling water that cooks your carrots in the kitchen will also cook your carrots in the garden, and there’s nothing magical about moving them outdoors that changes this.

So, with this in mind, using boiling water to kill and control weeds and unwanted plants can be very effective. Use boiling water to kill the weeds in sidewalk cracks, between pavers and even in the garden. As long as you keep the boiling water from touching your desirable plants, it makes a wonderful, organic way to control weeds.

Some plants are more tolerant to hot water than others, but trust me on this: before you attempt to heat treat your plants, get a very accurate probe thermometer to ensure you know the water temperature that you’re dumping on your plants.

How to Heat Treat with Water

Heat-treating plants is an age-old way of dealing with a variety of soil-borne pests, including aphids, scale, mealybugs and mites. In addition, many bacterial and fungal pathogens are destroyed within seeds left in water heated to the same temperatures required for killing pests. That magic temperature is just about 120 F. (48 C.), or 122 F. (50 C.) for seed disinfecting.

Now, you can’t just go around pouring hot water on plants willy-nilly. Many plants can’t tolerate hot water on their leaves and above ground parts, so always be careful to apply the water directly to the root zone. In the case of insect pests, it’s usually better to submerge the entire pot in another pot full of water in that 120 F. (50 C.) range and hold it there for five to 20 minutes, or until your probe thermometer says the inside of the root ball has reached 115 F. (46 C.).

As long as you don’t overheat the roots of your plant and you protect the leaves and crown from the heat, watering with hot water will have no harmful effects. In fact, it’s better to water with hot water than it is to water with very cold water. But generally, you should use water that’s room temperature so you protect both your plant and its delicate tissues from scalding.

Using Hot Water On Plants - Learn About Hot Water Effects On Plant Growth - garden

How Hot Weather Effects Plants

Hot, dry summers are rough on plants, especially on non-native plants and those weak from improper care. Since many of our landscape plants aren't naturally adapted to heat, they need special attention and care.

High temperatures speed up the normal living process of plants to a maximum rate at and above 90 degrees F. This means that most plants can take temperatures up to 90 degrees F. fairly well. Anything above that—the hotter it gets, the more they suffer! Of course, less tolerant or weaker plants suffer even more. The longer high temperatures persist, the greater the injury to the plant.

Hot soils also hamper plant growth. Shallow-rooted and container plants are particularly affected by soil heat build-up. Deeper-growing roots penetrate to a level of better soil temperatures and moisture. Mulching the soil surfaces around plants and watering properly is a good idea to stabilize soil temperatures. The most obvious symptom of a plant’s heat exposure and hot soils is persistent afternoon wilting, followed by foliage burn.

Hot air, particularly hot, dry wind, causes too much moisture loss from the plant's foliage. Some evaporation from leaves is normal, but when vital moisture is being evaporated faster than the plant's ability to replace it, leaves dry out and wilt. To be drought-tolerant, plants must have roots able to absorb as much, or more, moisture from the soil and do it as fast, or faster, than the foliage loses it. First symptoms of hot air injury are drying and browning at the tips and edges of older leaves. Then, tender new tip growth wilts, soon followed by dieback. Rapid moisture loss can cause tender leaves to turn black. Evaporation cools foliage, but if it doesn't get water from the roots fast enough to provide the evaporative cooling effect, the foliage gets hot, tender growth wilts and older leaves sunburn.

Exposure to the intense sunlight of bright, cloudless, summer days can be too much for sensitive plants. Reflected light from walls and other surfaces can also add to the problem. Stunted plant growth and a yellow-white "burn" on the upper surface of older leaves are familiar symptoms of too much intense sunlight.

A good covering of leaves protects the tender bark of branches and stems from sunburn. If this shading is lost, or pruned off, the exposed tender bark will likely sunburn.

When some nutrients are reduced or limited, or their uptake inhibited, deficiency symptoms quickly appear. Such is the case with iron during hot weather growth. Wet soils, dry soils, not watering deep enough, salty or caliche soils, etc. will decrease the amount of iron plants can absorb from the soil. The yellow foliage symptoms of iron chlorosis appear as greenish-yellow leaves with dark veins. As iron deficiency becomes troublesome, the green color of leaves turns to yellow, then to white and finally brown as the tissue dies.

Using plants adapted to our hot climate is the best way to get vigorous plants with minimum care. Some plants just don't do well in the heat! They're difficult to maintain and expensive to replace. Plus, plants suffering the torment of harsh surroundings don't offer a pleasing appearance to any landscape. Native, heat-hardy or at least tolerant plants are the most practical choices for local landscapes.

Tolerant plants resist moisture loss from their foliage, and are more efficient feeders on limited soil moisture. They can better tolerate intense sunlight. Tropical plants lose water rapidly from their lush, tender foliage. To make matters worse, their less efficient rooting is often unable to replace foliage moisture as fast as it evaporates in the hot, dry summer air. Remember—plants give priority to new growth when moisture and nutrients are short, so older leaves are deprived. This is why older leaves show hot weather injury first.

The life span of non-adapted landscape plants is much shorter. As they reach maturity, they lose the natural advantage of youthful vigor and the hot climate takes its toll.

Plant conditioning is important. Just as athletes must condition for endurance, plants also can endure hot, dry weather better if properly conditioned. Plant during a season when roots can establish quickly so that they're ready to supply plant needs adequately by the time hot weather starts. Fall (September to December) is an ideal planting time for the Southwestern U.S.! Transplanting during hot weather can be an exhausting experience for plants and gardeners. Proper watering and fertilizing favors good vigorous growth and the plant will better endure and recover from hot weather stress.

Plant location is very important. Shaded locations cut summer stress for heat- and sunlight-sensitive plants. Eastern exposures or open areas are generally preferred for blooming plants. Southern or western exposures are subject to direct, intense sunlight, as well as reflected heat. Because walled areas of these hot exposures build up and hold additional heat, only very heat tolerant plants can survive in these locations. Also, consider draft and wind exposure when positioning plants whose foliage may be particularly subject to burn by hot, drying air movement.

Soils that permit deep water penetration down through normal rooting depths, yet retain good moisture and nutrient content, are also important. Such soils favor the deep, extensive root development required to maintain strong healthy growth during hot summers. Heavy caliche soils can be improved by the addition of liberal amounts of organic matter along with clean washed sand.

Irrigation IS A MUST in order to maintain good plant vigor during hot, dry summers. Proper watering year round to promote deep extensive rooting is the key to summer hardiness. Be particularly careful not to over-irrigate during cooler seasons. Too much water drowns roots needed to supply enough water and nutrients to the plant during its peak summer needs. Keep in mind that all water used by plants comes from the soil. It's the most important of plant foods.

"How long and how often to water" depends upon how long the soil retains moisture and how fast that moisture is being used. A proper balance of moisture and air in the soil is necessary for roots to breathe and do their job. Irrigate to maintain favorable, not abundant soil moisture. Water long enough during each irrigation to allow moisture to penetrate completely through the plant rooting area, but no more often than necessary to prevent foliage wilt! Following this rule, and you'll automatically adjust to the age and type of plant as well as to the differences in seasonal requirements. Deep, penetrating irrigations each time also keep soil salts washed downward out of the root area. A drip irrigation system is THE MOST effective, efficient method of watering.

Fertilizing during hot weather should be done with caution, if at all. Increased living processes of plants during hot weather use up nutrient reserves faster. However, rapid uptake of fertilizers by summer-active roots could result in fertilizer burn. Increase the fertilization frequency, but decrease the amount applied each time. Fall fertilization helps plants recover from summer exhaustion. Spring fertilization encourages strong growth to better withstand summer stress.

Organic mulches spread over soil surfaces under plants provide a practical insulation against summer heat. Mulch shades the soil and keeps it cooler. It also reduces soil moisture evaporation, therefore cutting the build-up of salt at soil surfaces. But remember, mulches retain soil moisture longer. Continue to water deeply each time, but not as often!

Pest control is very important during hot summers. Any injury or loss of foliage would be more harmful to plants during hot weather. So watch for pests and control them before severe damage is done. Apply sprays during mornings or evenings.

So, regardless of how long and/or hot the summer will be, there IS a right way and a wrong way to insure that your plants thrive and survive.

Ugliness of Fruit Produced in Hot Weather
Virus, Bitterness and Temperature

If the "beauty is only skin deep" philosophy is true, then logically, it should follow that ugly is only skin deep too. If you can accept the fact that ugly is only skin deep, and that ugly and flavor are not necessarily culinary partners, then eating the malformed, odd-colored garden produce that shows up at this time of the year should not present a major problem. Regardless of what people say, most of us eat with our eyes—if something doesn't look right, most of us will think it doesn't taste right.

The bounty of the spring growing season has peaked and gardeners are now harvesting the final products of plants which have completed their life cycle. Most of the popular vegetable plants such as tomato, pepper, eggplant, beans, etc. are annuals, which means they have a relatively short-duration production cycle compared to perennial plants. As plants begin to senesce or grow old, the "fruits of their labor" begin to diminish in quality and quantity. Add to this aging process the onslaught of summer temperatures and it seems like “vegetables-from-another-world” become a reality in your own backyard.

One of the first complaints is "biting vegetables". You take one bite out of a seemingly normal cucumber or eggplant, and the quinine bitterness of that beast will take 6 bites out of your taste buds! You may have been harvesting normal, sweet fruit from these plants all spring and then suddenly bitterness dominates. Any stress on an eggplant or cucumber plant such as high temperatures, low moisture, low fertility or foliage disease can contribute to bitterness. Bitterness is associated with fruit harvested late in the season from unhealthy, poor-yielding plants. Once a plant produces bitter fruit, remove it from the garden because all subsequent fruit will be affected in a similar manner.

What about ugly vegetables? Much of the unsightliness of vegetables is also a function of plant age and temperature. Cucumber and squash plants often begin producing misshapen and gourd-like fruit. This is caused mainly by poor pollination and/or plant stress. Improper pollination caused by the pollen being killed by hot temperatures can cause misshapen fruit. Moisture stress during development can also misshape fruit. Some pollination did occur or the fruit would not be present but incomplete pollination resulted in the abnormal fruit shape.

Folks "eat with their eyes" and some of the psychedelic vegetable colors have gotten a few squeamish people abstaining from the table. Green tomato fruit have numerous spots about ½ inch in diameter with concentric, circular markings. On ripe fruit, these markings are alternate bands of red and yellow. Some gardeners think they have produced pinto tomatoes. This colorful fruit is actually symptomatic of the virus that was contracted by the plant. The virus is called tomato spotted wilt virus (TSWV) and is spread from plant to plant by tiny insects named thrips. It is too late now to cure the problem the fruit is perfectly safe to eat. The overall productiveness of the infected plants will be diminished. This is similar to, but not the same, virus which affects squash. Squash plants that once produced yellow fruit start to produce green, or often yellow and green, fruit. They may also have been affected by squash mosaic virus or cucumber mosaic virus. This virus is transmitted to your plants by insects that have been feeding on other virus-infected squash plants or perhaps some wild plant.

Do not confuse the symptoms of virus with the resulting effect produced by congregations of ravenous suckers called stinkbugs (so named because of the foul odor experienced when squeezed). After the fruit-suck-party has occurred, a large area of the fruit (tomato, pepper, peach, plum, pear, etc.) becomes yellow where the sucking damage has taken place. Sucking damage combined with hotter weather make the skin of tomatoes unusually tough at this time of the year.

The obvious answer to insure delightful looking as well as wonderful tasting, vine ripe servings for those who indeed believe that beauty is only skin deep and consequently, ugly is only skin deep too, is to peel the produce. My old mama used to peel tomatoes for her baby boy, but my wife decided the peeling was nutritious and a good source of natural roughage. Maybe my old mama didn't want her baby choking on those fruit skins or didn't want those tough skins getting under her dentures. I don't know who is right but I do know that my old mama NEVER put an ugly plate of tomatoes on the table, even during the summer months.

I've been gardening and writing about gardening for more than 20 years, yet I find I'm always learning new things about the plants, insects and other critters that call my backyard home. That's the great thing about gardening — it's never boring! I've worked as a landscaper, on an organic farm, as a research technician in a plant pathology lab and ran a small cut-flower business, all of which inform my garden writing. Someone once asked me when I'll be finished with my gardens, to which I replied, "Never!" For me, gardening is a process, not a goal.

Overhead watering isn't the most efficient from a water conservation standpoint, but there are times when it's called for. Photo: Suzanne DeJohn

During the hottest part of the summer, it's especially important to make the most of every drop of water. With so much information available it can be challenging to separate fact from fiction. Here are five common myths about watering:

    Myth: Plants need 1 inch of water per week

Although the "inch-a-week" recommendation is often cited as a rule of thumb, the truth is that plants vary widely in their water needs. Young seedlings and new transplants have limited root systems and need a consistent supply of moisture, so they may need daily watering if the weather is sunny and hot. Established trees and shrubs, on the other hand, may need supplemental watering only during extended dry spells because they have more extensive root systems. The amount of water a plant needs depends on a number of factors, including the type of plant, its stage of growth, type of soil, weather and time of year.

The best way to water most plants is by applying enough to moisten the plant's entire root system, and then letting the soil dry out slightly before watering again. Apply water slowly so it's absorbed by the soil rather than running off — a soaker hose is ideal. Avoid daily light sprinklings, which encourage roots to grow near the soil surface where they're vulnerable to drying out.

Rather than relying on a schedule, water plants when they need it. (Besides, how do you know when you've applied an inch of water with a soaker hose?)

Yes, wilting is a sign that the leaves aren't getting enough moisture, but that doesn't necessarily mean that the soil is dry. Anything that damages plant roots can cause wilting.

Plant roots need a fairly constant supply of both air and water. Too little water and the roots die from lack of moisture. Too much water and the spaces between soil particles remain filled with water, suffocating roots. Both situations reduce a plant's ability to deliver enough water to stems and leaves, resulting in wilting. Root diseases, physical damage (such as disturbing roots while you're hoeing) and soil-borne insects can also harm roots to the point that they can't fully hydrate the plant.

Damage to stems can also cause wilting. Some diseases and insects (especially borers) prevent water distribution throughout the plant, causing some or all of it to wilt.

The only way to tell if lack of water is causing wilting is to check soil moisture.

The soil was plenty moist, but this hydrangea still wilted in the heat of the day.

Water droplets won't scorch leaves, even on the sunniest day.

There are good reasons to avoid watering your garden on a sunny afternoon, but causing scorched leaves isn't one of them. The myth that water droplets act like tiny magnifying glasses and burn plant leaves has no basis in fact, and anyone who has watched the sun come out after a summer shower knows that the water quickly evaporates.

Leaf damage can be caused by all sorts of things, including:

-too much or too little soil moisture -fertilizer burn from improperly diluted synthetic fertilizer -insect or disease problems -weather conditions such as wind or frost

Try to avoid watering on sunny afternoons to minimize the amount of moisture lost to evaporation, but don't worry about leaf scorch.

Myth: Avoid overhead watering with a sprinkler

It's usually best to apply water directly to the soil around plants rather than watering with a sprinkler. Less water is lost to evaporation, especially on hot, sunny days. Foliage stays dry, minimizing disease problems.

But there are times when an overhead shower is called for. During dry, windy weather a fine layer of dust can build up on leaves, reducing the plants' ability to photosynthesize efficiently. Some insects, including aphids and spider mites, can be kept in check by simply hosing them off plants. Finally, heat-stressed plants that have wilted even though their roots are moist can benefit from a cooling shower — the effect won't last long on a sunny day but it may provide some relief.

Overhead watering isn't the most efficient from a water conservation standpoint, but there are times when it's called for.

Myth: Drought-tolerant plants don't need to be watered

Many young echinacea, sedum and black-eyed Susan plants have perished because these "drought-tolerant" plants didn't get sufficient water at planting time and during their first season of growth.

When you set out a new container-grown plant, the roots are confined to the shape of the pot. The plants need a consistent supply of water during their first growing season, until their roots grow out into the surrounding soil. Water them as you would your annual flowers in their first season. During their second and subsequent growing seasons, drought-tolerant plants may need supplemental water only during extended dry spells. Note, however, that just because a plant is drought-tolerant doesn't mean it doesn't fare better with a regular supply of moisture.

Even drought-tolerant types of plants, like these echinacea, need regular watering their first season or two, until they get established.

When you douse your plants, make sure the water reached the entire root system. In other words, water generously—not a little bit every day, Plunkett says. "It's important to water around the base of the plant, not over the flowers or foliage, and read the plant tag for specific instructions," Plunkett says. "When the water begins to flow from the drainage hole at the bottom of the planter, stop watering." And then, don't forget to pour the excess water off the planter saucer.

If, when you water your plants, the water immediately comes out of drainage holes, your plant is completely dried out, Plunkett says, and you should water it more often. If you're still unsure of how to best water your plants, you can purchase self-watering systems to help, Plunkett adds. Scotts Gro Water Sensor Starter Kit "is a fun way to remain aware of your plant's needs," he says. "The sensor is simply placed in the soil and the system calibrates to the plant's watering needs using a catalog of more than 50,000 plants. The device will monitor your plants and even alert you when water is needed through push notifications or email."

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Watering Plants? Use Cooking Water for Extra Nutrition

Share "Watering Plants? Use Cooking Water for Extra Nutrition"

We all have been at fault at some point in our lives for trying some crazy tactic for attempting to make our plants grow. Whether it is homemade fertilizer or sun lamps, everyone has their own tricks. Here’s another trick you can use to water your plants, plus its cheap and effective. This trick is to use cooking water from pasta and vegetables to give your plants extra nutrition. The next time you boil pasta or steam some vegetables in your kitchen, instead of pouring the water down the drain, use it in your garden or in your house to keep your plants green and flourishing. You can also use water from boiling eggs, which is full of calcium your plant needs to grow. This method of watering your plants works because it acts like a fertilizer to give your plants the nutrition they need to survive. This is a great alternative if you do not have the space or time to develop a compost pile.

How does this process really work? When you boil your food such as pasta, vegetables, eggs, or potatoes, many of the micronutrients such as phosphorus, nitrogen, and calcium are boiled off into the water. Therefore, after you have let the water cool down, not only will you provide your plants with a nice drink, the plants also get a bit of much needed fertilizer from the nutrients within the water. There are many advantages to using cooking water to feed your plants. Not only is it cost effective and resourceful, the fertilizer it provides for your plants gives them a more stable and steady growth period. The water will help promote natural nutrient storage within the soil. This means you will not have to fertilize your plants or garden as often providing longevity for your soil. It will also help your soil retain more moisture, therefore reducing the amount of times you will need to water.

There are various unique ways to fertilize your plants and provide that extra needed nutrition. For those individuals who are looking to save money and do not have the space to compost, then cooking water is for you. Its hassle free, environmentally friendly, sustainable, and it provides your garden with all the nutrients it needs to thrive. If this is your first time trying cooking water, start off slow. Don’t get too complicated while attempting to choose vegetables and other foods that you think will boil off the exact nutrients you need for your garden. Start with pasta and basic steamed veggies before attempting more creative organic ideas. I strongly recommend to supplement watering your plants with cooking water to give them that extra nourishment.

The Effect of Caffeine on Plant Growth



To explore the effect of caffein on plant growth, I planted, germinated, and grew mung beans. I introduced caffeine into the soil of some plants and evaluated the effects of caffeine on the experimental plants in comparison to the control plants that were not exposed to caffeine. Results showed that caffeine help mung beans grow faster with soil sprinkled with caffeine.

Difficulty of the Project
Safety Issues
Time Taken to Complete the Project



  • 1 packet of mung beans
  • 3 gardening pots
  • Enough soil to fill the 3 pots
  • Gardening utensils
  • Tap water
  • Caffeine tablets
  • Coffee powder
  • 2 beakers
  • 1 measuring cylinder
  • 1 digital weighing scale
  • 1 black marker


Some plants seem to benefit and grow faster when caffeine is added to the soil, while others seem to become stunted or grow slower. There are also some plants that are not affected by the presence of caffeine in the soil. Caffeine can be introduced to the soil by sprinkling grounded coffee over the soil, adding leftover coffee to the pot or watering with a caffeine solution made by dissolving a caffeine tablet in water. The grounded coffee is actually organic matter and will help in adding nutrients to the soil. It will also attract worms that feed on the grounded coffee and at the same time help to aerate the soil.


Experimental Procedure

  1. The independent variable is the solution used to water the plants – water, caffeine solution and a coffee mixture. The dependent variable is the growth of the mug bean plants. This is determined by measuring the height of the plants every day using a ruler. The constants (control variables) are the size of the pot, the concentration of caffeine and coffee, the amount of sunlight, the temperature of the environment (which will remain at room temperature) and the amount of water added daily.
  2. Fill the 3 pots with equal amounts of soil. Plant ten mug beans in each pot and allow them to germinate. Additional seeds can be placed in the pots in case some of the seeds do not germinate the additional plants can be removed later.
  3. For the first 5 days, water the 3 pots with tap water only. Allow the seeds to germinate for the first 5 days.
  4. After 5 days, measure the height of the 10 plants in each pot. Add up the individual heights and divide by 10 to obtain the average height. Record the average heights in a table, as shown below.
  5. Prepare the caffeine solution by dissolving 10g of caffeine tablets in 100ml of water in a beaker. Label the beaker ‘caffeine’. Similarly, add 10g of coffee to 100ml of water in another beaker and label it ‘coffee’.
  6. Label the 3 pots ‘water’, ‘caffeine’ or ‘coffee’. Over the next 10 days, water the pots once a day with 100ml water, caffeine solution or coffee mixture, according to the labels on the pots.
  7. Measure and calculate the average height of the mung bean plants every day for the next 10 days. Record all calculations in a table.


The results of the experiment were, mung beans grew faster in soil with caffeine.


The hypothesis that mung beans watered using a coffee mixture will grow the fastest has been proven to be true. The effect of caffeine on plant growth is still a subject under study. Using grounded coffee in garden lawns is a common practice to make plants grow faster. However, coffee also contains other ingredients like potassium and phosphorous, which are known to enhance plant growth. Experiments on plant growth using only caffeine have resulted in the plant leaves becoming wrinkled, turning brownish and exhibiting retarded growth.

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