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growing trees & shrubs with completely passive irrigation?  RSS feed

 
Bethany Dutch
Posts: 164
Location: Colville, WA Zone 5b
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I've got an idea in my head... let's talk about whether this would work.

I am researching various passive irrigation methods because in 2 weeks we're moving to our cabin on OUR land (WOOHOO!) and then I can start my homestead in earnest. One of the things I want to do is grow a decent food forest with lots of fruit and nut trees and shrubs... but generally we can't grow much here without irrigating. And, being the lazy efficient person that I am, I prefer to set up my projects so they have as little required maintenance as possible.

I've looked at air wells, using rock piles as condensers, hugelkultur, and other various methods and I'm thinking about combining them. So what I'm thinking about is, let's say, digging down a pretty decent way into the ground and creating a sort of sunken hugel bed. Then, plant a tree in the middle of the hugel bed. I'll mulch it with something decomposable (or not) and also pile up the earth so it's pointing downhill towards the tree itself at a slight slope, so sort of forming a donut around the tree.

So then I'll cover the circular area around the tree with black plastic, and perforate the plastic at intervals around where I think the root ball will be in the first 10-15 years of growth. I'll leave the first few feet around the tree uncovered, so that the water won't run down and soak in right at the trunk. In a few places I might poke the pointy tube end of a turkey baster into the ground at one of the perforations, all of this to encourage water that condenses to run down the plastic and into my perforations and/or dug in turkey baster tubes and therefore right to where the roots are.

On top of the plastic I'll make rockpiles - big, small, not sure what just yet. But I'm thinking again, emulate the donut shape with the rockpile so that there's a depression in the center (or actually I might need to leave the center completely open, you think?).

So my thinking is that the rocks will cool off overnight and then during the day the warm air will run through them, condense, drip down onto the plastic which will then channel it to the perforations/turkey baster tubes and on down to the roots. The rocks also would do double duty and shade the plastic while the moisture collects, preventing evaporation. The decomposing wood and everything in the Hugel will do what it does and retain more moisture.

A few issues I can see with this - I don't know how I'd be able to add organic material, and I can see junk and leaves building up between the rocks over time which would impede the airflow between the rocks and therefore the condensation. And I'm not certain the plastic will even be necessary, although my first thought was to use it so I could direct the flow of water better. But them I was thinking maybe it would just be better to just build a smaller pile to start with and then increase the size of the rockpile every year as the tree (and therefore root ball) grows in size.

Thoughts? ANything else I could combine with this idea? I don't want to use a lot of high tech (expensive!) stuff
 
Alder Burns
pollinator
Posts: 1363
Location: northern California
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I think the two basics to always keep in mind are 1. adapted species and 2. establishment. Look at what other people are growing in your area and which trees apparently are thriving without irrigation. Work with those and their close relatives first. Then, remember that just about any plant in an arid or semi-arid climate go through a recruitment phase.....the young seedlings establish in that one year in several to many when there is above-normal rainfall, and roots penetrate deeper into moister layers. So you need to simulate this with some supplemental water for the first season or two, no matter what kind of niches you create... Because of this it's good to plan carefully and not plant more than you can nurse along and get water to, fence against critters (another important establishment practice).....
 
Peter Ellis
Posts: 1432
Location: Central New Jersey
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Off the top of my head, without knowing anything about where you are and how much your area requires working at forms of irrigation/water collection.

Why use the plastic? You say so you can direct where the water goes for the tree, but as long as it is getting into the ground around the tree, seems to me we can trust the tree to find the water. I see the plastic catching and holding water away from the ground, despite your intentions, preventing air flow that is needed by the soil life, and the tree. I don't see the plastic having a beneficial role.

Hugelkultur around a tree? I think that's not really a proper use of the word, since you're not talking about growing loads of plants on there - it sounds more like you're doing a really rough sort of mulching, and I don't see it being very productive. Trees shouldn't be planted directly into hugels, as I understand it, for a number of reasons, including that hugel beds will tend to settle, and that the tree won't have a very strong attachment to the ground beneath the bed for some time - which can lead to an uprooted tree if the winds are too much. Trees right at the end of a hugel bed, or along the edges, don't have the disadvantage of actually being on the bed, but get the benefits of the increased moisture and general soil improvements, plus they can help with wind across the bed and reduce evaporation loss in that way.

No problem with using the rock piles to catch some condensation, as far as I can imagine.

Depending upon where the tree is located (slope, soil, overall climate) it might make sense to do a sort of collection basin around the tree, by making a sort of keyhole shaped berm with the opening on the uphill side, and a swale that spills into the berm through the keyhole. Lawton describes an interlocking web of these as a way of utilizing a slope that's too steep for other purposes.

More information about your property would help people give you better advice
 
William James
gardener
Posts: 1014
Location: Northern Italy
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As for using rock piles as condensers, I looked into that solution and I found that the amount of rock pile needed is huge. The original rock pile condensers were something like 2m high and wide.

As I didn't have that many rocks, I abandoned the idea. But small rock piles here and there are beneficial for other reasons, even if they don't accumulate that much water (compared to what 1 tree needs).

William
 
Bethany Dutch
Posts: 164
Location: Colville, WA Zone 5b
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Well - we live in NE WA about 90 minutes north of Spokane so it's definitely 4 seasons here. Summers usually get up to high 90s or low 100s for a couple weeks, and winters generally get down to a lot of about 15 with about 2-4 feet of total snow accumulation. Spring and fall sees a decent amount of rain. Our soil is beautiful.

We don't get super duper dry, but it does get hot in the summer and we generally need to irrigate. Our property has a good variance of places to plant - I am not sure where I'll plant the trees just yet. I actually do have a steep drop-off right east of the house, with a flat bench below which I'd planned on turning into a tree growing area. I actually have been thinking about sugar maples there, so that maybe one of my grandkids (my oldest kid is 7, so a ways away yet) could make some syrup

HOWEVER

I do like the idea of planting a tree at the base of the slope and creating a keyhole type berm around it to trap runoff. That would be perfect, I think. As far as the hugel, I was going to plant the tree into the hugel which would be buried, so it wouldn't actually be raised at all. But that's assuming I feel like doing major excavation.

The plastic thought came from something that happened this summer which actually originated the idea, although like I said above I wasn't really sure if it was necessary.

This summer, we ended up having no garden. We ourselves (me, husband, three kids) are living in a camper next to my parents house, who also live on the property about a half mile away from our homesite. My mom and I were both having some big health problems this spring so while we did start plants in the greenhouse that's as far as we got. Mice ate the starts, we were sick, so didn't feel like bothering with it.

So then midsummer I decided to go into the greenhouse (keep in mind it's been upper 90s weather for weeks) and I see a few totally lush growing tomato plants inside the greenhouse, growing out of the dirt floor.

So it looked like we'd dropped a few seeds during our sowing in the spring and there was a way that some plastic was draped on the inside (initially it was to keep the heat inside for the seedlings when we did our sowing in early March) and from what I could tell, there was condensation that built up inside the greenhouse which then dripped down the plastic within root distance of the tomatoes.

They grew all summer even with their late start and we didn't water them once. The last one just died a few days ago, actually, and it's been pretty cold (below freezing at night) for a couple weeks.

So - it got my wheels turning. If I could accidentally grow tomatoes in a super hot greenhouse with zero irrigation here, I SHOULD be able to figure out how to passively irrigate a tree and/or other plants. I don't know if the plastic would help by channeling water, or if it would just hurt the situation.

We do intend to intentionally experiment with growing more tomatoes in the greenhouse and see if we can duplicate the conditions. I was actually thinking about encouraging the moisture/condensation by growing duckweed inside the greenhouse in a kiddie pool, but haven't really done much research on that yet... different topic for a different day

Oh and regarding rock pile size - I've heard about people who use them on a smaller scale with some success - I can't imagine they would provide all of the tree's daily water needs, but it seems like it should help. Gotta figure out a way to encourage the humidity to condense and collect somewhere before it evaporates.
 
Jennifer Wadsworth
Posts: 2679
Location: Phoenix, AZ (9b)
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If your property is sloped, installing swales on contour would probably be your best bet as these would slow any precipitation and allow it to sink in and rehydrate the soil. A soil that's hydrated will keep growing things even in hot weather, especially if heavily mulched. One of the things geoff lawton tried to hammer into our brains during his PDC is that swales are tree growing systems. They are designed to slow and spread water, rehydrate the landscape and form the basis for a food forest. No need for plastic (which would suffocate soil life and make it less likely eventually to hold water). In your climate, you would grow your hardy native support species (legumes) on the uphill side of the swale and your fruit and nut trees on the soft berm on the lower side of the swale. The swale (always installed on contour) catches and slows precipitation and soaks that extra water into the downhill berm where the fruit/nut trees are. Meanwhile, the hardy legumes stabilize the uphill side of the swale and fix nitrogen into the soil. They also benefit from some of the extra water that collects and soaks into the swale, but less so than the downhill species.

Now your accidental experiments with the tomatoes reminds me of something we're forgetting here.

First step - identify where the top of your watershed is on your property. If you live on a very sloped property and your house is halfway down the slope, the high point is going to be the highest piece of land. If, on the other hand, you live on a very gently sloped or flat piece of land, or at the top of a sloped piece of land, the top of your watershed will most likely be the tallest roof on your property. Because water flows downhill, you want to work from the top of your watershed, down. I'm betting that what happened with your tomatoes is that water condensed on the outside of the greenhouse, flowed down the sides and hydrated the soil enough to keep the tomatoes going. The same principal can be applied to any point in your watershed. Water is going to run off hard surfaces. Make catchment down hill from these to hold, soak and spread the water.

Second step - Consider greywater sources. Bathroom sinks, tubs/showers and washing machines all provide a lot of greywater that could be used again in the landscape. In the Spokane area, you could probably rehydrate land just off greywater alone. Here in Phoenix, I build an outdoor shower with hot and cold running water - I use it 365 days a year. It waters shade trees and grape vine which grow over the top of the shower, henyard and propagation area. I can literally eat grapes while showering.

One of the things you have to remember is that the goal should be to rehydrate the whole landscape, not just the areas around trees, etc. Focusing just on watering in one are almost guarantees that you'll be using supplemental irrigation indefinitely. Geoff stated in his PDC that he's found he can rehydrate any landscape within 7 years - and we're talking about the "greening the desert" property in Jordan here too! Not just the easier climates like the one he has in Australia (rehydrated in 3 years). Good soil that is rehydrated across the landscape will grow great trees/shrubs/anything adapted to that climate. Remember the support species as well as the fruit trees. These support species should probably make up about half your trees in the more temperate climate you're in (they make up about 75% here in the low, hot desert).

I really, really recommend you get Brad Lancaster's two books "Rainwater Harvesting for Drylands and Beyond, Vol 1 and 2" Volume 1 is an overview and volume 2 goes into earthworks in great detail.

 
Bethany Dutch
Posts: 164
Location: Colville, WA Zone 5b
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Jennifer - thank you! That was very informative... going to read it again and let it soak in. I think I agree with you on the swales - especially since we do have this one spot that is perfect for them. I"ll have to do more reading up on them but I think that will really help.
 
Jennifer Wadsworth
Posts: 2679
Location: Phoenix, AZ (9b)
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Hey Bethany - keep us posted on what you try out - it sounds like a wonderful project. Brads books are pretty self-explanatory and will certainly help visualize a plan.

Best,
Jen
 
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