The Effect Of Drought On Plants?

How Are You Coping With The Effect Of Drought On Plants? Wilting Plants, Flower & Fruit Drop, Lost Yields. Here’s How To Survive Drought.

Most plants are very dependent on water and The Effect Of Drought On Plants is very noticeable.  Wilting plants, drooping and scorched leaves, leaf rolling, flower and fruit drop, brittle leaves and yields drop is just the start. In the extreme the plant will die.

Few plants have truly adapted to coping with a lack of water. Those that have tend to store water in their stems or other fleshy parts so they can survive when water is restricted. As a group they are called xerophytes. They survive in deserts where there is little water, on salt marshes and similar where water uptake is restricted by salt and in frozen places where the only water is frozen. Garden plants can’t survive these conditions and need plenty of water to not only survive but grow, flower, fruit etc.

Some gardeners create special gardens for plants that can cope with reduced water availability. These hardens practice xeriscaping. At the extreme this might be a cacti garden. In the UK we have some well known xeriscape gardens such as Beth Chatto’s Dry Garden in East Anglia (East Anglia gets less rain than Jerusalem) and Derek Jarman’s shingle garden near Dungeness.

But the above are the exception at present, though could become more normal as global warming bites. In most cases plants get enough moisture to transpire, grow and thrive.

Plant Transpiration & Evapotranspiration

Plants absorb water through their roots and expel most of it it though their leaves though a process called transpiration. This then contributes to evapotranspiration which is how water moves from the earth’s surface into the atmosphere. It covers includes both water evaporation and transpiration.

Transpiration is a natural process where water is absorbed by the roots and moves through the plant. As it does it provides the means by which plant nutrients move around the plant. A small amount of water will be retained by the plant but the majority, around 97+% is lost to the plant via transpiration and guttation. This helps cool the plant during hot weather.

Some water is lost though the stems and flowers but most of it is lost via the leaves. Fortunately the plant can control the water lost within certain limits. The water goes out via pores or “little valves” on the leaves. These are called stomata. The tomato have a cell on with side of the stoma which can open or close the stoma. Most stoma are on the underside of the leaf and can be seen via. hand lens.

The plant can vary the size of the stomata pore size (aperture) to control the flow of water. Transpiration is also influenced by external factors such as temperature, humidity, wind, and sunlight. Hot windy sunny days with low humidity will see more water lost than still cooler humid days. The plant allows for this when controlling the stoma pore size.

Stomata are the structure through which the plant also gives off CO2.

What Causes Drought?

It would be easy to imagine a lack ion rain or irrigation is the primary cause of drought. But it isn’t that simple. The answer often lies in the soil and this was very evident in a field of maize I recently looked at. Most of it seemed to be growing quite well, but some areas were severally stunted, the plants had rolled their leaves and the leaves were being to loose their colour and die.

The reason wasn’t the lack of rain. If it had been the whole field would have been affected. Most of the field looked good visually. I’m sure it could have been better if wed had more rain, but visually it was doing OK.

The reason that whole areas were short of water goes back to let winter. At that time the farmer had been dumping farmyard manure in the field. he’d driven across the filed with heavy tractors and full trailers in some very wet weather. The soil had been churned up. This leads to a loss of soil structure and soil compaction. the rain can’t penetrate the soil and runs into the streams. What little gets into the soil is then trapped there when the soil dries. The dried soil forms a pan, like a lid, over the lower layers. The plant roots can’t penetrate it and then suffer when there’s a drought.

The Effect Of Drought On Plants … .Continued

Drought Effects on Plants

The plant has to balance its ability to obtain water from the soil with its need to transpire. If it doesn’t transpire it doesn’t grow and if it transpires but can’t obtain water via its roots it was also die.

But these are extreme cases. Long before this happens a plant that is under drought stress starts to close its stomata and balance the flow of water to match its ability to obtain more water. As well as reducing stomata size it wil start sending roots deeper in to the soil as it seeks to find more water. Therefore a good deep soil where the plant can grow deep roots is better for plants than a shallow soil.

Plants start to take action long before we see it. That means that plant growth is often reduced without us noticing it and that if conditions were abetter wed get better, more vigorous plants that produced more flowers, fruit, roots or whatever were want to harvest rot enjoy. Most plants never reach their genetic potential due to adverse growing conditions. Drought is one of those conditions. But plants will always notice it before humans do!

As well as reducing stoma size and send roots deeper plants have other strategies. One is to roll the leaves. This is typically seen on tomatoes and new gardeners often panic when they see it. It’s perfectly normal and nothing too worry about provided it isnt too extreme. It means the plant is hot and can’t find enough water to transpire and cool itself. The plant then rolls its leaves to reduce the leaf area exposed to the sun and to create some shade for itself. That’s normal.

But if conditions don’t improve the plant starts to lose more water than it can get from the roots and the leaves wilt. Wilting reduces water lost. But if it goes on too long the leaves eventually dry out and go crisp. They die!

The good news is that these conditions don’t last forever. At night the moisture lost reduces and the roots start to win the uneven battle it experienced during the day. Leaves start to regain their turgor and “perk up”. So being able to find water overnight is good for a plant. Watering late evening or at night therefore makes sense.

Should the drought continue for a long time then the plant really starts to suffer. Growth stops, it can drop existing fruit (June drop in apples is an an example of drought prompted fruit drop), flowers don’t pollinate, flowers drop off etc.

One major impact of drought is reduced photosynthesis. We might have enough sunlight, but an excess of sunlight means plants start to shut down their systems and photosynthesis then stops.

Long Term Plant Response to Drought & Adverse Growing Conditions

When a plant has suffered previous drought it will succumb more quickly a second time that season. It’s already in a weakened state and isn’t going to be so reliant. Think about it in human terms. If you have a bad cold or Covid when you catch something else, or suffer a trauma, you aren’t going to be as resilient. It’ll knock you harder.

And stress going back to previous season can also impact. If the plant suffered severe stress last year then its not as strong this year and will suffer more. Again, in human terms, if you already have a bad back, a broken leg is going to be even harder to cope with.

But don’t think a good life will make everything right.

If the plant had it too good, perhaps with loads of water and nitrogen, its growth will  be soft. Leaves will be plentiful and more fleshy than normal. That makes it vulnerable to drought. More, softer leaves lose water quicker than a “fitter” plant!

Plants suffering from pest and disease also suffer more in drought conditions. And the reverser is true. Plants suffering from drought more easily succumb to pests and diseases.

Drought Evolution Response to The Effect Of Drought On Plants

Where climates dictate plants will evolve to cope with drought. For example woodland plants that grow under tress suffer water and light deprivation when the tress leaf up in spring. They’ve therefore evolved a repose mechanism. They flower earlier and die back earlier.

In British woodlands we see bluebells, primroses, foxgloves and other plants flowering in spring and dying back once the tree leaves grow.

Other plants have evolved to be shorter as a response to drought.

Drought Prompted Avoidance & Tolerance Mechanisms

As well as growing shorter plants have devised other ways to cope with drought stress. Some have waxy leaves that prevent water lose. Others grow hairy leaves which can also reduce water lose.

These mechanisms help them cope but the payback is that the plant is less productive. The plant might be happy with this, but gardeners want productive plants.

Root changes are a major way in which plants cope with drought. Some plants use the roots or tubers as a storage organ in which to store water and nutrients. Other grow extra long roots that go deep down to where water can be found.

What Can We Do To Reduce Drought Stress in Plants?

There are many management practices that gardeners can adopt to improve the situation. Remember drought tends to start later in the season rather than earlier.

Early Planting To Avoid Drought

Planting early means plants can mature earlier and avoid the later drought. Clearly going too early means cooler or even cold weather so we have to compromise between early and too early.

Dense Planting To Avoid The Effect Of Drought On Plants

If plants go closer together there are many benefits. Though there are more plants and the total consumption of weave tis higher per unit area it is easier to control mulching. watering etc on a small area.

Dense planting also reduces the sunlight reaching the soil and reduces soil moisture evaporation. Bare soil gets very hot. Vegetation provides some shade to the soil which means the soil surface is cooler as is the soil temperature a few inches down.

A lawn with longer grass suffers far less drought stress than a closely mown one. In times of drought raise the mower blade and leave grass a bit longer. It can still be tidy… just. bit longer.

Drought Resistant Varieties

Some varieties are more drought resistant than others. Choose the rather than those that need too much water.

Drought Resistant Species

Celery is a marsh plant. It would be madness to grow it in drought conditions. It makes more sense to grow crops that are more drought adapted than celery. Thats virtually every vegetable you can grow.

Choosing The Right Soil & Vegetable Combinations

Many gardeners tell me carrots love to grow in sand. They don’t actually, they prefer a medium to heavy soil to prosper in. We like a stone free sandy soil for them as they grow straighter. The problem is when drought strikes the sandy soil dries out quickly and the carrots suffer. If we take more care about matching soils and plants wed suffer less drought.

Mulching As A Drought Avoidance Strategy

Mulching helps prevent the evaporation of moisture from soils. Within reason the deeper the mulch the better. The mulch also reduces soil temperature.

Adding Organic Matter To Beat Drought

Adding organic matter to the soil, either incorporated or as a mulch will improve the ability of the soil to hold water.

Irrigation Of Drought Threatened Plants

Irrigation or watering is going to help some plants. But it needs careful consideration. Little and often is a bad strategy. It just wets the surface and encourages plants to produce shallow roots. Less frequent but heavier amounts make far more sense as it encourages deep rooting and makes the plant more resilient.

Hand watering makes us consider which plants need water and how much. Mechanised watering tends to lump water on indiscriminately and uses much more water. A farmer might water whole fields of crops such as potatoes at certain times. But it is carefully considered, partly because it costs so much money. We need to consider every litre we use in gardens as well.

When choosing an irrigation system cost, ease of use and many other factors need to be considered. The biggest issue is where is the weather coming from. Water is getting scarce so we need to harvest and store as much as sensibly can.

Gardening Systems To Beat Drought

The way we garden is going to impact our drought resilience. The use of organic material in the soil definitely increases water holding capacity but there’s a bigger issue. Each time we dig, plough, rotavate or even howe soil we lose soil moisture. that’s one of the reasons I have moved to No Dig gardening. I know it’s a Marmite subject and some people hate the idea of not digging. But No Dig retains soil moisture for several reasons. Firstly its not turned so soil moisture evaporation is reduced. And secondly the incorporation of organic material increases soil moisture capacity. Thirdly the surface mulch reduces evaporation.

Rain Water Harvesting & Storage

Having a way to harvest water, either rainwater or grey water, is a great starting point if we are to beat drought. I’ve written several longer articles on this and they can be found by following the links.

Rain Gardens

Rain gardens are another way to retain water in your garden. They are designed to prevent rainwater going down the drains, and having time too soak into your soil. This means your subsoil gets its share of water and stops the drains being overburdened when it rains excessively hard.

Shade As A Drought Tolerance Strategy

Shade reduces drought stress in plants. So temporary shade is a possible strategy when the weather gets excessively hot. Temporary shades can be made of cloth etc.

More permanent shade can be produced by dense planting and by the use of screening. An open weave fence panel slows airflow and provides shade. In decorative and flower gardens this can be a useful way to reduce drought conditions.

More on The Effect Of Drought On Plants

There is much more I can write on The Effect Of Drought On Plants, and I’ll add more posts on the post in future