The Gardener's Almanac

Water & Watering

Water / watering is something most of us take for granted but don’t necessarily know its importance in gardening terms.

For instance; why do we water?

It is to replace water that is lost via transpiration from stomata (closable pores on the leaves).

That is, stomata open when the plant is ‘turgid’ (swollen or distended with fluid) and they are letting in air containing carbon dioxide.

When water, carbon dioxide and sunlight react they make sugars, these sugars are the plants energy source, this reaction is known as photosynthesis.

If a plant runs short of water, the stomata close and photosynthesis can stop, leading to slower growth and possibly the failure of flower buds to form and fruit to develop.

During the dryer summer months plants depend on reserves of water in the soil, when this is lacking it must be supplemented by irrigation to keep the stomata open.

This supplementary watering is important for the production of strong, healthy plants, i.e. plants that are watered sparingly but often produce a root system close to the soil surface and these roots soon suffer in dry periods.

The healthiest plants are those that develop a strong, deep root system which is able to tap into more reliable reserves well below ground level.

This then creates the problem of knowing when to water;

Watering in the evening allows the water to drain deep into the soil / compost over night, and early morning watering should be done before the heat of the sun builds up and causes evaporation.

Note; Time of day to water can often be dictated by the life style, and work commitments of the amateur gardener, rather than the needs of the plants, so if you find that your plants are wilting, water them straight away.

If practical; move those in pots into the shade, or throw a sheet of fleece over those that can’t be moved to protect from the sun until they recover.

As a rule-of-thumb, a square metre of vegetation can draw the equivalent of about 25mm (1”) of rainfall from the soil every day.

There are a number of ways to establish if conditions are too dry; e.g.

Leaves can begin to droop.

The soil can feel quite dry when touched.

These two symptoms on their own do not necessarily mean the plant is suffering from lack of moisture, for instance when conditions are exceptionally hot, plants can wilt then recover when the temperature drop again, and the first few millimetres of soil may dry out in the sun making it feel dry to touch.

It is best to inspect the soil deeper down by excavating a hole to one spades depth, this will give a better indication of conditions at root level, and if watering is required.

Applying water;

Ideally one should apply water at a steady rate, in effect at a rate that emulates steady rainfall.

Too much water at once can cause soil erosion and compaction, plus it can wash away nutrients.

There are many types of equipment available to the amateur gardener for applying water to the soil, each with there own benefits and / or drawbacks, here are a few;

Watering cans;

These can come in varying sizes (capacities) although two are quite popular, i.e. 1 litre (1¾ pints) and 5litre (2 gall).

The former is generally used with pot plants where only small quantities have to be treated, the latter are useful where there is a need to just water a few or individual plants as opposed to the whole bed.

Hosepipes:

Before using these one must ensure that there is no ‘hosepipe ban’ in your locality.

While this method of watering is more convenient, it is often more wasteful, and sometimes damaging!

You will often find that; some plants get more water than others, and non planted areas are watered thus encouraging weed growth!

Plus the wetted area makes a good skid pan for slugs and snails to navigate to your plants.

There are a number of ‘hose end’ attachments that can be fitted to hoses that allows the user to vary the intensity of the spray.

However! if the pressure is too great, you can damage plants, spoil flowers, damage the soil surface, and wash out nutrients.

Similarly the water may run off the designated area before it has a chance to percolate down to the root system.

When watering with a watering can, each plant is more likely to get an amount of water relative to its needs, and the surrounding area is left dry, wich acts as a deterrent to slugs & snails.

Sprinklers:

These tend to be used on lawns where they are allowed to spray water in a side to side or circular motion.

They have limited use on flower or vegetable beds due to the expanse of the spray, that is, the water goes on to areas that might not necessarily require watering to the detriment of the areas that do, meaning they use huge amounts of water.

Leaking / seeping hoses;

These are hose that have been purposely perforated to allow water to seep out.

In some cases these hoses can be used on the soil surface and placed adjacent to rows of plants where the water seeps out and percolates down to the root systems.

On other occasions, such as with permanent fruit trees and plants with deep root systems, the hoses are sunk permanently along the length of the rows of trees.

In both cases it is possible to fit the hose/s to reservoirs that allow soluble liquid feed to be added to the irrigation system.

Similarly these hoses can be fitted with automated watering systems where an electronic timer is screwed to the tap to turn the system on/off automatically.

Frequency;

Check your local forecast for the week ahead on one of the many ‘Weather Forecast’ sites on the internet?

Generally all you have to do is pop your postcode in a designated spot to get your local weather forecast for the week ahead, this might eliminate the need to water at all

It is better to water well rather than often!

If too little water is applied, this will only moisten the upper layers of the soil and it will not get down to the root system where it is needed, necessitating further watering a short time after.

If in doubt, check by digging a hole with a trowel / spade to see how far the water has percolated down.

Water only to an area consistent with the plants optimum spread.

Watering out with this area will encourage weeds and create a moist surface that is suited to slugs & snails.

Types of water;

Some plants need soft or acidic water to thrive.

Many domestic water supplies contain calcium and magnesium, which can raise the soil pH.

Water from recognized ‘soft water’ areas can have calcium added at the treatment works to improve its drinking quality.

Avoid giving hard water to ericaceous plants, as water above pH7 can cause chlorosis or yellowing of foliage, thus affecting photosynthesis and the subsequent health of the plant.

There are products on the market that will remove calcium and other impurities from tap water.

Rainwater collected in water butts is slightly acidic making it suitable for all garden plants.

To prevent the formation of algae cover the water butts to keep out sunlight.

What and when to water with a view to conserving water;

Never water plants when the sun is on them as this will waste water through evaporation.

Mulching over the soil surface will prevent evaporation and so help to keep the soil below moist.

Never add mulch to dry soil or the mulch will draw water away from the soil instead of holding it in, soak the soil first.

Water saving/collection;

Investing in one or two water butts not only helps to save water, but for those with a water meter it saves money too.

The butts can be located to collect rainwater from any downpipe on your house, garage, shed, greenhouse or conservatory.

The butts can be linked in series with plastic connecting fittings*, these connections ensure that; when the first butt is full, water flows through the connecting pipe to fill the second butt and so on.

*Available from DIY stores and garden centres.

Note; Always replace the lid of the butt after use to discourage algae growing and prevent mosquitoes breeding.

When the butt runs dry, take the opportunity to scrub it out thoroughly, and remove any debris that's accumulated in the bottom.

This task should be done as a matter of course at least once a year.

Greenhouse watering;

Unlike outdoors! Keeping plants grown under cover supplied with sufficient moisture to meet their needs can often be quite daunting, particularly when you consider; in very hot weather, they may need to be watered twice a day.

Invariably this task has to be done manually! Luckily there are a few things you can do and use to make things easier.

For example; placing pots on capillary matting set in shallow gravel/water trays allows the plants to absorb water when they need it.

Damping down the floor of the greenhouse with water every morning will increase humidity and reduce drying out.

Good shading and ventilation will also reduce rates of evaporation.

Investing in an automatic drip system with a built-in reservoir, should take care of most of the necessary plant irrigation required, particularly at holiday time.

Bedding plants; need regular watering in dry weather, and are better watered either first thing in the morning or during the evening when the sunlight is not as strong.

Planting out at wider spacing can reduce the need for water; the closer plants are the more water they need.

Containers; Even after bouts of heavy rain, it is surprising how little water will actually reach the compost due to the ' umbrella effect' of the plants foliage! often resulting in bone dry compost.

At the height of summer; containers may require watering more than once per day.

A hose pipe is generally the most convenient method way of doing this, particularly, if it is fitted with a ‘U’ shaped lance.

Note; There are now spring loaded devices available to fit to your hanging basket that allows you to pull it down to the height most suitable for watering.

When locating baskets and containers; always locate them at a height that is convenient for watering.

As an alternative; revive hanging baskets and portable containers by soaking them in a bucket of water.

Submerge the whole pot, root ball and all, and leave it for a couple of minutes to soak through.

Once all the air bubbles have escaped, remove it from the bucket and let it drain before replacing it in its flowering location.

Established lawns; can survive a period of drought and will soon turn green again when rain arrives.

If is important to keep grass green give it a good soaking* once a week.

In dry periods mow frequently but keep the mower blades at their 'highest' setting.

Close cropping can stress the lawn in periods of drought, whereas long growth will trap any dew.

New lawns; A lawn of newly sown grass seed or newly laid turf will need regular watering* in dry weather.

Large shrubs and trees; deep rooted plants can find water for themselves and rarely need watering in dry conditions.

If they have been recently planted they will need regular watering until they have created a healthy root system.

* Provided there are no hosepipe restrictions in place, watering with a hose/sprinkler is the simplest method of keeping it well watered throughout the summer.

Avoid using valuable mains water supply by diverting 'grey', waste washing up / bath water from the house.

Small shrubs; when established, can generally find water for themselves, and rarely need watering.

They will start to droop when they require water, when this occurs give them a good soaking in the early morning or evening when the sunlight is off them

Perennials; can be treated like small shrubs

Fruit & Vegetables; As with any other crop; fruit and vegetables need a regular supply of moisture to produce good crops.

The need for manual watering can be substantially reduced during summer, if the soil is pre-prepared the previous autumn/winter with the addition of humus in the form of farm yard manure, or home made compost.

An exception can be on light or thin soils, where the use of mulches can reduce evaporation.

After planting mulch the area/s with a thick layer of mulching material such as; farm yard manure, home made compost, spent mushroom compost or shredded tree/shrubs.

This mulch will conserve moisture and keep weeds at bay, thus reducing the competition for available moisture & nutrients.

If manual watering is required; then a hose fitted with a multi- spray head is generally the best method, although it might be worth considering a ‘seep hose’ for permanent beds of currants, raspberries and strawberries.

Watering vegetables every 10-14 days should be sufficient for them to cope providing they get a good soaking at each of these occasions.

If sowing seeds give the drill a good soaking prior to sowing.

Similarly when planting seedlings flood the planting hole prior to placing the plant in the hole, this will ensure that there is moisture at the point where it is needed most.

Vegetables may need extra watering at the time when they are at their peak of development e.g. ripening or swelling.

Examples;

Crops such as legumes respond best to additional watering at flowering time

Watering Potatoes at flowering time will greatly increase the numbers of tubers and subsequent watering in dry spells will boost tuber size.

Root crops and alliums (onions) are less reliant on additional water so it is not essential to give them additional water.

Leafy crops such as lettuces and cabbages ideally need a constant supply of water throughout their growth.

Where this is not possible, give them a good soaking 14-21 days before their intended harvest.