Both the soil structure and the amount of organic matter in your soil will affect how long it takes for your soil to be filled up with water and retain that water for your plants.
Sandy and silty soils will drain very quickly and not hold moisture very well at all, whereas clayey soils drain very slowly to the point of readily creating boggy conditions.
Ideally you want a soil that is somewhere in-between these two extremes; a soil that holds water well yet capable of draining away excess moisture so that bogginess does not occur after watering. The solution is organic matter.
Organic matter drastically increases the water holding capacity of sandy soils while it also breaks up clayey soils preventing bogginess. So in reality the first thing to know about watering actually has nothing to do with watering itself so much as it is about understanding soil and the magnificent properties of organic matter. (Learn more about soil texture & particle structure.)
Deeper roots makes for stronger plants for many reasons. The most obvious reason is that deep roots anchor plants firmly in the ground. But other major benefits from a deep root system include a much greater soil volume to pull nutrients and water from.
Deep rooted plants are much more likely to survive drought and even poor soil fertility. How you water your garden will greatly influence crop rooting depth, and the best way to encourage deep rooting is to water DEEPLY but INFREQUENTLY.
What exactly is meant by deeply and infrequently?
Gardeners need to think of their soil as a large underground reservoir. When you water your garden, the goal is to literally refill the ‘reservoir’ underneath your plants. You want to fill the soil volume to capacity with water. Depending on soil type, garden size, and the amount of organic matter in your soil, this may mean leaving the water on for 1-2 hours. This thorough soaking is what is meant by deep watering.
Once the soil reservoir is filled to capacity with water the garden won’t need to be watered again several days or even weeks, which allows your crops to gradually drink down the reservoir before it’s refilled again; this is what is meant by infrequent watering.
The beauty of this system is that it encourages very deep root growth which in turn creates stronger plants. With the soil reservoir full of water, the water at or nearest the soil surface gets used up first. After surface water is used up, plants begin to draw water from deeper within the soil. Deeper water is not exposed to the heat or wind like surface soil is, therefore water losses due to evaporation are virtually non-existent.
As the soil reservoir gets used up and begins to empty (both by being pulled up by plants or by slowly percolating downward through the soil), only the very deepest water is left remaining. This forces crops to send roots downward. And it also gives the crops’ roots a chance to breathe in between waterings, which is really important. We often forget that plants’ roots need air. Unless a plant originated from a swamp its roots will appreciate being able to breathe from time to time.
On the surface, filling a soil reservoir sounds like it uses up a lot of water. But remember the infrequent part of the equation: for example, over a six day period if you water for two hours one day and then not water again for the other five days that’s equivalent to watering only 20 minutes each of the six days; that’s not very much water especially if you have a big garden.
Some crops can go longer in between waterings (as much as weeks in some cases) and other crops enjoy water a little more often, but even most water-hungry crops can be trained to go without waterings for up to three days or more and perform quite well.
Crops can be grouped into two basic “watering preference” categories, based on the type of crop they are. These two groups are 1) the leaf and root crops; and 2) the fruit and seed crops.
These two categories describe the part of the crop that is consumed. For example, leaf and root crops are crops such as carrots, turnips, lettuce, beets, spinach, potatoes, cabbage, kale, celery, etc. The fruit and seed crops include crops such as apples, oranges, peaches, cucumbers, pecans, cherries, walnuts, watermelon, pistachios, squash, tomatoes, cantaloupe, etc.
- More frequent and less deep watering is preferred, and actually encourages, leaf and root growth in plants. Thus leaf and root crops should be watered more frequently at about 2-3x per week.
- By contrast, less frequent and deeper watering is preferred, and actually encourages, fruit and seed growth in plants, thus fruit and seed crops should be watered less frequently at about 1-2x per 1-2 weeks.
For your convenience, we have created a chart that lists crops according to crop type (including those crops listed that are exceptions to the rule). The watering recommendations given in the chart are general guidelines that may require adaptation depending on each gardener’s unique circumstances such as high or low temperatures, humidity, elevation, rainfall, etc. Our watering recommendations were actually developed from the Intermountain West of the United States where we used to live. There the summers were consistently in the 90’s (30’s in Celsius), humidity was really low, it rarely rained, and we were approximately 4,300 feet (1,300 in meters) above sea level which makes for a more intense sun.
Remember that these watering guidelines apply to established crops; that is, crops that have already been in the ground for a while and have a mature root system. Freshly sown seed or recently transplanted crops need to be kept moist but not swamped to help them grow and establish well. As crops grow you should begin gradually watering less frequently and more deeply.
When should I water?
The best time to water is during the cool of the day when evaporative water losses will be minimized. This means watering in the late evening, at night, or in the early morning. Although all these times will work just fine, early morning is the best. Pre-dawn temperatures are usually the coolest of the day, winds also tend to be at their calmest, and the hot sun is still back behind the horizon. If you’re not a morning person but still want to take advantage of the ideal watering time of pre-dawn, there are many inexpensive sprinkler times that can be set to turn your water on at 4 or 5 in the morning.
When she was growing up, Anni’s father used this method for many years, because of some interesting geographical features in the area. I’ll let her tell you about it in her own words.
*Addition by Anni* Where I grew up, this technique (that we’ve talked about above) was called ‘subbing’, and it worked really well because in northeastern Idaho there is a lot of old lava rock, left behind by ancient volcanoes. (In fact, just a couple of hours north is Yellowstone National Park, and a couple of hours southwest is the Craters of the Moon National Park.)
In that particular area, there’s a layer of lava rock which sits only 15-20 feet down (which is quite shallow) throughout the region. A lot of the farmers in the area used to flood their potato fields, using the canal and ditch technique. There’s a network of canals running from the reservoirs through the farming communities, and a matrix of ditches around the fields (mostly potatoes). In the spring, after the water gates were opened in the reservoir, the water would flow down the canals, finally reaching where we were at, on the Egin Bench area.
Then farmers could open up the sluice gates to their ditches and water would fill the ditches around the fields. And then they would walk down their fields, opening up notches in the ditches, enough for water to flow into the furrows along each potato row.
After 5-6 hours (from my memory), the whole field would be flooded, and the farmer would make his way back along the ditch and fill in the holes in the ditch bank. Some farmers had made it more efficient by building pipes directly through the ditch bank, with valves that could be easily opened and shut so they wouldn’t have to use a shovel to dig into the ditch bank, and then fill it back in (which was an inevitably muddy process).
By doing this, the fields would be flooded with a great deal of water, it would sink into the sub soil, and then when it hit the lava rock barrier, it would be wicked back upwards through the soil to the top of the soil. (That’s why they called it ‘subbing’…. sub-irrigation.) Then it would take a great deal of time to filter through the somewhat porous lava rock, or flow outwards to surrounding areas, the plants’ roots would follow the water slowly downward, giving them depth, stability, and strength, and the field wouldn’t have to be watered again for a week or two.
There were also small ditch dams, made of metal sheets, placed every so often along the whole length of the ditch. They allowed the water to flow, but slowed it down so the water would have time to flow into the furrows and sink into the soil. I couldn’t find a picture of one, but this was the basic shape of those old ditch dams.
We were surrounded by potato and wheat fields that were consistently flooded all summer. Because the soil reservoir would be filled in all the fields around us, when my father would flood the garden with water from our ditches, it would easily fill up the reservoir under the soil down to the lava rock layer, and it would take a long time for it to flow outward into other soil areas, because they were full of water too.
Then things changed. When I was about 8 or 9 years old, a lot of the farmers in the area started investing in the big boom sprinklers on wheels that would rotate around the fields (like in the picture to the right) because the subbing technique did take a lot of the farmer’s time. So instead of flooding the fields every couple of weeks, they were watering on the surface of the soil every other day or so.
Because the sub soil beneath the fields surrounding our garden weren’t filled up with water, the usual method of flooding the garden had to be done more frequently because the water would dissipate much more quickly out into the empty sub-soil beneath the fields that surrounded our garden. My father still uses sub-irrigation some, but he has sprinklers now too.
Using the sprinklers is actually a much less efficient method of watering because a lot of water is lost to evaporation either when the sprinkler sprays it out over the field or while it’s sitting on the top of the soil (the sprinklers were always going, even in the heat of the day).
The subbing technique actually used less water. Sprinklers are much more convenient, though, in a lot of ways which is why farmers started using them. They can be automated, and they just rotate back and forth across the field (or around in circles, depending on the layout of the field). And farmers can put pesticides, insecticides, and fertilizers in the water and have it automatically sprayed on the field.
The northeastern Idaho area is one of the few places in the world where sub-irrigation can be done, and have it be so effective. In fact there’s a monument describing it. My mother was kind enough to go take a picture of it for me. It’s about 100 yards down from the primary school I went to, in Parker Idaho. It says,
“The Egin Bench Area settled in approximately 1880 is watered by sub-irrigation, a system rare in the world. Customary surface flooding irrigation did not work in this deep sandy soil.
The pioneers found that a natural substratum barrier trapped canal water, thus raising the water table to water crops from below the surface and draining enough to prevent alkalization of the soil. The early settlers thanked the Lord for the miracle of this special feature. The system is monitored through small holes throughout the fields to gauge the water level. The construction of this irrigation system of canals, ditches and dams was a community effort and covered about 50,000 acres of land. It is still in use today.”
I wish the sub-irrigation technique was still used. I can’t really blame the farmers. They’ve got a lot of pressure to produce more and more food that can be sold as cheaply as possible. But it’s depleting the water reservoirs, spraying tons of pesticides and other chemicals all over the land which is sinking into water supplies, and the land is becoming worse instead of improving every year.
I tend to romanticize my growing up years a bit. I was a wanderer. During the summers I criss-crossed potato and wheat fields and jumped across ditches. I used to love watching the big boom sprinklers wheel slowly around the field and smell the water in the air. But now that I’m older I think perhaps remembering some of the old way of doing things might actually be better.