How to Get Water to Plants and Trees in Drought Conditions

Where I live, we usually only get a few days of rain every so often and when it rains it is usually only a small amount. We have food plots that need to be watered.  Then there are the flowers for the pollinators, the butterflies, bees and birds.

How to get water to plants and trees in drought conditions or if you live in the dessert?

Here are some threads on different ways to get water to the plants and trees.

This thread mostly covers using Mulch:

https://permies.com/t/89965/dry-climate-leads-sustainability-mulch


This thread has some information on Zai Holes:

https://permies.com/t/96852/permaculture-projects/Starting-Food-Forest-soil-crazy




This thread is about Air Wells - collecting water from the air

https://permies.com/t/airwell


This thread is about Wicking Beds:

https://permies.com/t/134410/Wicking-beds-Texas




This thread is about Clay pots or Ollas

https://permies.com/t/56986/Clay-Pot-Irrigation-Experiment




This thread is about Keyhole Gardening:

https://permies.com/t/68883/permaculture-projects/keyhole-garden-summer-drought


Some information on Rainwater Catchment:

https://permies.com/t/36676/Brad-Lancaster-Waste-Transform-waste#285925

https://permies.com/t/127073/store-water#1040876


This last thread is about Dryland Farming:

https://permies.com/t/58559/permaculture-projects/Big-Fat-Thread-Dryland-Farming


Let's have a discussion on how and why these work.

Anne,

Super interesting topic!  Of all the ways to acquire/retain moisture I only have experience with two forms.  The first is drip line irrigation which is very effective and waters far better than overhead irrigation and/or flood irrigation, but this almost seems like cheating compared to the other forms of irrigation you mentioned.

The other forum of “irrigation” I utilize is mulch, and lots of it.  Where I live, having a nice, thick mulch is a guarantee that I will retain available moisture in the soil beneath.  My climate zone (6b) is generally humid, but mid to late summer droughts are not unheard of.  My clay soils used to turn brick hard under punishing summer heat and about 3 weeks without meaningful rain.  That brick-hard clay was death to anything with fine, shallow roots.  I have found that a good mulch (meaning, not just an inch, more like 6 inches and more is better) really holds on to moisture at depth, and actually merges with soil, as opposed to bordering soil.  The benefit for me is that the otherwise dry, hard clay stays moist, loose and friable throughout the heat of summer.

The short version is that while I have used drip irrigation before I discovered mulch, now I simply no longer need drip irrigation.

Eric

Anne,

So do you have a preferred method of getting precious moisture to your plants?  I realize we live in quite different climates, what with mine being quite moist & humid.  I typically consider a drought to have begun after 3 weeks in high heat and no rain.  By that I mean that if we get to say, 4 weeks of high heat and no rain, I consider this to be a 1 week drought.  It seems like that is how long it takes plants (aside from trees which have plenty of access to water deep in the soil) to dry out and start showing heat stress.

From memory, it seems like from the time we first bought a house in the region, we had about 3 very dry years out of the first 5-7.  We have been lucky in the last 10 to have had no serious drought conditions.

These may seem ridiculous to you as 4 weeks without rain is nothing to you, but it does make a difference to both our soil (dense, brown clay) and our annual crops.  At first I was sold on drip irrigation for watering my garden beds and fruit patch.  But I have not run the irrigation system in several years, and I have no need to since I started applying thick wood mulch that I chip up myself.  It works so well that the top of the soil and bottom of the mulch kinda merge together, with there being no obvious boundary between the two.

I realize that you have a totally different climate condition compared to me, so I was wondering what worked best for you.

Eric

Actively following the thread, as this is one of my biggest needs. After getting the water bills last summer, I've decided there's no way I can afford to irrigate an annual & forest garden, plus the stuff in containers, with the local municipal water. Historically, most of our rainfall has been in spring (including the occasional, light flooding). Then late May- Sept are usually dry, with little to no rain & low humidity. Around October we begin to get a few, small showers.

As of now, I don't have a lot to contribute, as things are still being put in place. Since, in theory, we get enough rain in spring to last the entire growing season, I'm trying different things to keep as much rainfall as possible on the property and in the soil. The two most successful plans, so far, have been deep mulch over the wet ground and buried wood in a modified hugel bed. The buried wood by itself helps a lot, but it seems to hold & release moisture more steadily if I include other OM with the wood, like rabbit manure, chopped weeds, and similar things.

One thought I had to try this year was to do a thick layer of carbon mulch on the surface, then chop green weeds/vegetation and, instead of putting them on  the top of the mulch, I could bury them under the carbon on the soil surface. My thinking is that the large percentage of the plant that's water would go into the soil and/or mulch, instead of evaporating when drying on top of the mulch.
Has anyone tried this?

Zai holes and air wells were new terms for me. Interesting discussions in the links!

My area is dry and humid from around May to September. Last summer, it rained twice during the 3 hottest months. I have a couple of barrels for collecting rainwater, and I mostly rely on mulch. I want to invest in some ollas.

Temperatures reach the upper 90s, so I try to protect some of the plants and ground as I can. My garden is in full-sun, so I've been adding bushes and structures that can provide some shade during the hottest part of the day. It rarely rains when it's time to plant summer crops, so I use milk jugs to prevent the soil from drying out until the seeds germinate. I just cut the bottoms off and shove them into the ground over the seed. And I strategically leave some "weeds," mainly those with large rosettes that are shading the soil. No matter how hot and dry it is, it seems like it's almost always damp and cool under those leaves.

Kc Simmons wrote:
One thought I had to try this year was to do a thick layer of carbon mulch on the surface, then chop green weeds/vegetation and, instead of putting them on  the top of the mulch, I could bury them under the carbon on the soil surface. My thinking is that the large percentage of the plant that's water would go into the soil and/or mulch, instead of evaporating when drying on top of the mulch.
Has anyone tried this?

I was just thinking today "what a shame" after seeing the dried out plants that I'd tossed onto the mulch a few days ago. I may try this during the really dry months, shoving the green cuttings under the wood/straw mulch, especially the more succulent vegetation. Seems like that moisture would be good for the microbes at least.

I just thought of a third way I have irrigated.

As I stated earlier, I don’t really irrigate anymore, but I once tried a technique that is halfway between drip irrigation and some techniques mentioned here.

I once tried a milk jug irrigation system.  The technique was really simple—get a gallon jug of milk and poke little tiny pin holes in the bottom.  It will only take 1-2, maybe 3.  Then sit the jug next to or in between plants, fill with water and that’s it.  The water will slowly soak out over a matter of hours, delivers a precise amount of water that soaks right into the soil.  If one really wants to get ambitious, the jug can be buried, delivering the water underground, right to the root zone, with no evaporation losses to the surface.  The technique couldn’t be any more simple.  As I remember, I was growing 8 tomato plants and I buried 2 jugs, each surrounded by 4 tomatoes.  It was cheap, easy, and effective.

Just a thought,

Eric

Eric said: Anne, So do you have a preferred method of getting precious moisture to your plants?

My best method has been to plant drought tolerant plants.  My plants are mostly 3 or 4 years old so they have developed deep roots.  The one along the fence did not get watered at all last summer.  They are blackberry, honeysuckle, autumn sage, and turkscap.

The ones in the butterfly garden are blue sage and rosemary.  We planted two rose bushes last year so I did water that bed for them.



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One year, I planted sweet alyssum.  I love it for its sweet smell. I also found that it work as a mulch to hold in moisture.



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I have had good results with a deep watering wand, using well water from my pressure system. I push the wand into the soil (shallow for garden, deep for fruit trees), turn the water on low, and walk away for an hour. If you have mulch on top, it's basically undisturbed

At my previous property, the well was shallow and had enough dissolved mineral to burn strawberry and squash leaves if it had direct contact. But the plants were quite tolerant of brackish water underground.

I always made my own wands from things like a discarded downhill ski pole. My next one will be from a pressure washer wand, which is easier because it already has a water fitting and thin, strong tube.

Anne,

Very sensible to plant the heat loving and drought tolerant varieties.  This is probably the very best way to plant w/o lots of water.

Do you grow veggies too?  How/do you irrigate those?

Eric

Eric said: Do you grow veggies too?  How/do you irrigate those?

Great question!

I have Egyptian Walking Onions that I planted in the Butterfly Garden.  I do water them when I water the roses.  

I also transplanted maybe half of the Egyptian Walking Onions to the bed that we had planted tomatoes.  Either the tomatoes didn't like the onions or they just didn't do well.  So the onions got watered when the tomatoes were watered.

Dear hubby is the vegetable gardener.  He tried drip irrigation and mist irrigation though he prefers to just water with a sprinkler for 15 minutes a day.  We have a timer attached to the outlet where we attach the garden hose.

I usually buy squash transplants and I am the person who waters them.  I usually water them with the sprinkler.

Our food plots are planted with a mix of oats and milo. We tried the deer mix that the stores sell though it was mostly purple hull peas and turnips.  The deer liked the peas though they did not eat the turnips.

In 2017 we has a food plat that we grew with sunflowers.  Here is where I documented the project.

To water the food plots, we have an 8 ft flatbed trailer with a water tank like this one:



We attach a pump with several garden hoses.  That method works well for us since we can't depend on rain.

Where I'm located, the average temp is over 90 F for 5 months of the year, and for two of those the average temp. is 100 F.  Rainfall can range from 7-12 inches a year, with the majority of the rain coming down halfway through the summer for about 2 1/2 months.  Humidity when it's NOT raining, but IS hot, can be down to single digits during the hottest part of the day, and we have a very high evaporation rate, which is very hard on the plants, obviously. I grow both native species, drought resistant species, and also try my hand at veggie gardening as well.

My experiences with water, plants and drought conditions, good and bad, is the following.

Mulch based on plant matter -
The success of this depended a lot on water availability and amount of mulch.  Because of the high evaporation rate, the ONLY time large amounts of mulch worked (4-6 inches deep) was when irrigation was involved.  So around some of my fruit trees and garden veggies that I regularly water, it was tremendously useful. To not waste water, you have to have a set up that adds in the water UNDER the mulch, however. So a hose that goes into a section where the mulch is absent, or automatic watering systems that the mulch was put on top of, for example.  The water gets to the soil this way, the mulch breaks down slowly, and it helps tremendously to keep the soil in the ground.

But if mulch from organic matter is used when there isn't irrigation, it can't be thick or it doesn't work well.  Rain events can't penetrate the mulch and the water is simply absorbed by the mulch and released back into the air before it gets to the ground. And on top of that, any mulch that is wood based doesn't break down for a LONG time without a large addition of water.  Things here desiccate rather than decay, with a little help from insects, typically - there's an old fallen tree that's been on a hiking trail for 10 years now, and it looks nearly the same as it did when it fell over, except for where termites have eaten it.

So for native plants, or drought hardy plants I don't water as often, I still add mulch, but it's typically a 1-2 inch layer, and the pieces have to be cut smaller if I want them to decay.  This way, the rain can still penetrate, but it does help cover the soil and prevent some evaporation, and as long as I irrigate every once in a while, it usually will decay.


One solution for this particular issue that I do instead is, I guess I'd call it mulching with stones.  Rock or sand mulch (covering the entire area with 1-2 inch layer of small rocks/gravel/sand) is really popular here, and is also terrible - no nutrients get to the soil, and it raises the temperature of the surrounding area quite a bit, making it more difficult for the plants as well.

However, once a med-large sized plant is established, and casts a bit of shade, I can go back and place some large stones underneath it, making sure they have full contact with the soil.  I usually pick ones that are 4-12 inches wide. I'll put a few around the plant in question, with the spaces between the stones having that 1-2 inch mulch. It works fairly well, so far. It is kept moist underneath the stones, but the soil still has areas where it can absorb nutrients from decaying mulch.  

This does not work, however, until there is shade. It is so hot here that if you put large stones around a smaller plant, in the sun, they'll heat up things so much they stress the plant and sometimes have killed it.  

Ollas -
I have tried some homemade terra cotta ollas and they have done so-so, but I think that's more a case of my forgetting to add water to them than anything else. ^_^ One thing I did notice, however, was that with my high evaporation rate, the penetration of the water from the olla wasn't as far FROM the olla as expected, so there might be some experimentation needed with this with regards to one's evaporation rate and spacing, you know?

Oh! With re: to using plastic milk jugs as an olla for watering - I am highly jealous of the ability to do this, LOL.  One CAN use plastic out here, but it is so hot and brutal that it destroys the plastic fairly rapidly, so you can't use it for anything that you want to last.  I've tried milk jugs but within a few months, they are so brittle you can grab them and the plastic basically disintegrates in your hand.


drip lines -
I have had to avoid these, although they are popular here.  But I live a little out in the boonies, and anything that might have water, the critters are usually desperate to go after during the worst of the heat, when it hasn't rained. I have had so many destroyed hoses and lines from these critters.  

Although if anyone else has this problem, I have been having some success with putting out little shallow dishes of water near but also AWAY from the garden and watering equipment. That seems to cut down on the destruction of my equipment.

It had an unexpected benefit too.  Animals here can REALLY find water, wherever you have it. But what that has meant is that even if I have a garden fairly well camouflaged with plants that mask the sight and smell, the critters will STILL find my garden by following the presence of the water.  Putting out these little shallow dishes of water has cut down on that issue as well.


Shade -
Because of the intensity of the sun here, it's extremely rare to have any issues with a plant that can't get enough sun, but the sun itself causes a lot of water loss IN the plants. So finding ways to add dappled or partial shade has been helpful for keeping water with the plants during the driest parts of the year.  Usually, it does well enough with slightly bushy trees to the west/ south west of the plants, to help them the most during the summer months.  Mesquite trees are good for this with native plants I don't need to water. Pomegranate and texas persimmon have worked well for more garden oriented plants, and shade cloth in a pinch.

Also, a sort of 'personal' shade for some plants can be helpful as well.  I planted some greek oregano in a spot that DOES get shade during the heat of the day due to a wall, but I thought it had died, and just let native grasses grow over it for a year as I forgot about it. Come back later, when dead clump grass has fallen over it, and the oregano used the dead plant as shade for its base and was happily growing through it. I have a clump now that's probably 3x3 feet, and I might water it 2-3 times a year. If I try to weed it, it gets dry and struggles. If I let native weeds partially take it over, so it has to creep up through them, it flourishes.  The ground is always noticeably more damp underneath the shaded, weeded oregano than the surrounding area.

That is something I have noticed in this area - shade is king. I'm sure this is not the same in areas without such intense heat/sun, but for me, it's a vital part of planning with water and plants.


pit-type gardens -
The past few years I have used a Zuni style pit, the kind of 'waffle garden.'  This does all right here, but while we get little rain, when it DOES rain, it comes down so hard that it tends to eventually wash away the walls of the waffle gardens, no matter how hard you make them, even with stone mulch on top trying to keep them safe.  I'm sure with more maintenance I could keep them going, but I'm hoping that zai pits will be better for this climate and need less maintenance, so we'll be trying those this year.

Keyhole gardening -
Does not work so well here if you are looking for water conservation.  Again, it's mostly because of our intense heat and high evaporation rate.  This is an issue with raised beds of any kind here - the sun significantly heats up the soil down to about 2 feet. So anything that is raised up tends to get much hotter soil, and the plants need a lot more water, and even compost piles here have to be covered or they tend to dry out too fast.  I mean, you CAN get it to work, don't get me wrong. I know people who have done keyhole gardening here, but it's a lot more difficult, and it's not good from a water conservation standpoint, and most of them had to build a more complicated set up to keep the compost more enclosed above the ground so it didn't lose too much water.

Dryland farming -
Also does not work so well here, except during one tiny part of the year...and even that's iffy. While we are often within the range of dryland farming when it comes to rainfall, the heat and low humidity are so brutal that it makes it nearly impossible. The rain also comes so seldom that most plants cannot sustain themselves long enough, no matter how awesome they are (native plants are the exception, so I'll talk about that in a sec).  The one time it might work is during the middle of the summer, when the monsoon rains come.

Midsummer IS a growing season here - there is the possibility for setting up a dryland farming scenario during this time. I know that the native tribe here, in the past, made garden beds in these small areas that flooded during the rains, and vegetable varieties were used with short growing seasons. But the flooding areas collected water from a number of arroyos, and it's nearly impossible to get that amount of water from your yard, even when you are trying to collect it, you know?

That said - there are a lot of native plants that are sources of food that do perfectly well in an environment like this.  They don't need watering - I have a lot of plants that I don't water in the slightest and can get food from every year. A lot of cactus and native trees that are legumes, mostly. Some native herbs and greens that are seasonal. It's not the most exciting diet, but it would do, in a pinch.  One just has to adjust your thoughts away from 'what do I want to eat' and shift it a bit toward 'what can grow here.'


And...ha, yeah, didn't mean to go on so much!  This is such an interesting topic, though!  And in part I wanted to share what my own experiences are because many of these were ideas I looked at when I first started out, and they kept failing and confused the heck out of me. I finally realized that while many of these methods discussed rainfall conditions, most didn't really talk about heat or humidity, or any other condition that might impact water usage and retention. When I investigated, most of the methods that did not work here were from areas where the heat was lower, the humidity was higher, or the method in question had more water due to irrigation or rainfall.  

Shauna, thanks for sharing! Lots of great info!

Shauna said: I'd call it mulching with stones.  Rock or sand mulch (covering the entire area with 1-2 inch layer of small rocks/gravel/sand) is really popular here

Thank you for sharing your experiences!

What you said about the rocks is what I have found works.  I don't take advantage of this though.

I put some big flat rocks on some plants that I wanted to kill.  After being there several days I went to remove the rocks.  I found that instead of killing the plants ... they were being "watered" by the rocks.

I live in a temperate climate so water isn't a major problem here, however due to climate change the temperature has been breaking records year after year now.
Last 2 years we've gotten summers with barely any rain and temperatures rising up to 30-40°C. Groundwater levels are also heavily depleted by a lot of farmers who use giant sprinklers to water their crops.

So right now i am trying to prepare my beds for a new potential drought.
I have a manual water pump of which i don't know the depth of. (I just recently bought this piece of land) So as it can be an aid i can't fully rely on it, also it is very labor intensive.

My current approach is i added some beds with comfrey, which roots very deeply and creates a lot of leaves.
So the idea is that i can pump up water (and nutrients) as these plants can reach great depths and the leaves are then used as mulch, giving back their moisture and nutrients to the top soil.
This will never be a complete irrigation system but it can be another aid in becoming irrigation-independent and other plantspecies might be suitable as well. These plants are most of the time also great for beneficial insects.

Oh, just thought of something else that might impact drought and plants that is a bit more on the unexplored side, but could be something interesting to check out!

Plant communication during drought conditions.

I've seen more than one study now on plants communicating with each other, and one of the things that is communicated is drought conditions, typically via the root system and Mycorrhizal networks created by fungi in the soil.  For example, plants have communicated with other species of plants when a drought hits and it encourages the other plants to prepare for drought as well (like to close their stomata and slow down water loss, for example). It helps more plants have less water loss.

It's something that makes me wonder if planting in ways that encourage more roots intermingling, or with plants that are more sensitive to drought intermingled with other plants (I know they exist, but don't know what they are, yet), could be helpful.  Also, the thing permies talk about anyway, good soil and fungus, might be helpful not only in healthy soil, but also in our plants getting a slight edge in preparing for droughts more rapidly.

I haven't seen a lot of research in how much of a difference this makes, practically speaking, but it's a fun concept to explore, you know?

I live in a place that is mostly wet, but we can get dry periods.
In particular, I have a rubble filled plot of land that has no city water available to it.
I don't worry about the established trees, but I would like a way to water the raised beds.
They do OK all things considered, but last year you visibly see the gourd vines wilting in the heat of the day.

I have considered making a kind of large olla out of  buckets, barrels or trash cans.
To mimic the permeable nature of a real olla, I would cut holes in the containers, but cover the openings with cement or mortar.

To fill the ollas, I have considered a system, consisting of greywater filtered and collected in an IBC tote that sits on a small trailer.
When the water in the IBC nears the trailers capacity, I would hitch it up to my vehicle and drag it one block over to the yarden.
There it would be pumped into another, elevated IBC, and distributed from there.

I like this plan because I could could use the IBC on the  trailer for other bulk things, simply by cutting the top off.
I would acquire the elevated IBC tote for the yarden first.
It could be filled by rain water and a tarp, until things got dry, and at that point I would need to bring the water over.

shauna carr wrote:Oh, just thought of something else that might impact drought and plants that is a bit more on the unexplored side, but could be something interesting to check out!

Plant communication during drought conditions.

I've seen more than one study now on plants communicating with each other, and one of the things that is communicated is drought conditions, typically via the root system and Mycorrhizal networks created by fungi in the soil.  For example, plants have communicated with other species of plants when a drought hits and it encourages the other plants to prepare for drought as well (like to close their stomata and slow down water loss, for example). It helps more plants have less water loss.

It's something that makes me wonder if planting in ways that encourage more roots intermingling, or with plants that are more sensitive to drought intermingled with other plants (I know they exist, but don't know what they are, yet), could be helpful.  Also, the thing permies talk about anyway, good soil and fungus, might be helpful not only in healthy soil, but also in our plants getting a slight edge in preparing for droughts more rapidly.

I haven't seen a lot of research in how much of a difference this makes, practically speaking, but it's a fun concept to explore, you know?

I think you are absolutely right! i've gotten myself into the soil food web a bit aswell and i think it is almost ridiculuous these natural systems get barely any attention at all, as they are at the base of all landlife.
The advantages are almost indefinite as every organism is linked together to become one big organic system, creating an extremely resillient environment.
But hey, where's the money in that

Lots of shade is helpful. In hot climates you can get by with just a few hours of morning sun or even complete shade for plants like lettuces. The shade reduces water evaporation and reduces plant heat stress. The only way I can grow leafy vegetables in my Australian summer is in full-day shade.

Thanks everyone for all the great comments!

I thought I would share some of the other things that I do to help in a drought situation.

We made our soil for our raised beds out of a mixture of compost, leaf mold, manure and of course dirt.    Over the years I have been adding coffee grounds to it.  I save the coffee grounds in a 3 gallon bucket and when it get full I put the spent coffee grounds in the garden.  Any organic matter that is placed in the soil will help reduce the need for water.

I like to use ollas like I referenced earlier.  These can be a simple DIY system or even just a clay pot.






Another thing that I do is plant taller plants where they will block the wind.  Wind causes evaporation, which means the soil is becoming dryer.  These plants help by blocking the wind and also adding some shade.
   
What Plants are good for blocking the wind? Corn is one of the ones we use.  Tomatoes and pepper can help smaller plants like lettuce. Squash is another.

Here are a couple examples:

Anne Miller wrote:Thanks everyone for all the great comments!

I thought I would share some of the other things that I do to help in a drought situation.

We made our soil for our raised beds out of a mixture of compost, leaf mold, manure and of course dirt.    Over the years I have been adding coffee grounds to it.  I save the coffee grounds in a 3 gallon bucket and when it get full I put the spent coffee grounds in the garden.  Any organic matter that is placed in the soil will help reduce the need for water.

I like to use ollas like I referenced earlier.  These can be a simple DIY system or even just a clay pot.






Another thing that I do is plant taller plants where they will block the wind.  Wind causes evaporation, which means the soil is becoming dryer.  These plants help by blocking the wind and also adding some shade.
   
What Plants are good for blocking the wind? Corn is one of the ones we use.  Tomatoes and pepper can help smaller plants like lettuce. Squash is another.

Here are a couple examples:

Your garden beds are beautiful! I have had success with basil and banana plants blocking harsh afternoon sun and hot winds too.

Shauna, how did the zai pits work for you? I'm thinking of trying them in my unirrigated Bulgarian garden with less than 18" rain a year and very hot dry summers that seem to be getting hotter and drier. What little rain does fall in summer is very light, it barely wets the ground before evaporating, so mulch isn't a good option unless I can get water to the plants. I'd love to try terracotta ollas, but they can't be left out over winter as the freeze breaks them. I will try plastic bottles part buried, but suspect I'll have the same issue you do with plastic getting brittle very fast.

I am fortunate enough to live somewhere that tends to have plenty of fresh water and adequate rain throughout the season. This however has been changed up recently near the end of the growing season where drought conditions set in and have made me consider how I can best prepare my homestead to be more water-wise when it comes to crops and gardening.

I am a big advocate for deep mulch. I primarily enjoy it for ease of weeding out undesirable plants. I further enjoy it because after putting down the mulch and letting it mellow for a year, the ground is easily planted into going forward. Unintentionally for my purposes but most welcomed, deep mulch helps regulate moisture for plants when it comes to extremes. I can move a few inches of woodchip by hand in the hottest parts of summer and generally find a patch of moisture underneath. I am a big advocate for introducing beneficial fungus to gardens and have read that mycelial networks can help plants overcome drought conditions.

Thought I would mention a great resource on this:

Gardening When it Counts by Steve Solomon

His main point is that you need to open up your plant spacing for dry conditions.

Lots of other ideas there also.

https://archive.org/details/gardeningwhenitc0000solo

I don't think it's so simple.
There are many levels and types of dryness. If we are talking about something like Sahara or Sonora desert, then yes, all the plants there have adapted to grow with large superficial roots, and to store as much water as possible in leaves, trunks or bulbs. In these conditions, plants have to be planted far from each other.

For less draught barren lands, plants can survive being closer to each other as long as they are adapted to the amount and frequency of the rainwater pattern. However, there are not many crops that we like to eat that are so adapted to draught. So we end up growing 'thirsty' plants, meaning that they want more water than what they get from the rains. One way to grow thirstier plants is giving them more space, the extra space is meant as water catchment areas that need to be clean of plants and maybe soft tilled.
But what happens when you have five months of draught, like it is the case here in my city? If your plant is not adapted to a draught so severe, it doesn't matter if you can catch more rainwater, the soil will probably be as dry as a stone in a couple of months and your plants will die. There's the option of capturing rainwater in barrels and irrigate as needed, maybe useful for a small lot.

Another option is using microclimate techniques as a way to reduce the total lenght of draught. With good shade, better soil, some extra area for water catchment, protection from dry winds, sfsf, maybe instead of five months of draught, the soil can behave like a three months of draught soil. There are many more crops that I can grow adapted to a three months draught, but not the commercial tomatoes and peppers every market gardener likes to grow here.
So it has to be a combination of protected soil for reducing the draught conditions, and better adapted plants. The extra spacing would be required for thirstier plants only.