Wicking Beds for Palms

[Jonathan]

The thread about pots with high drainage holes reminded me that I should show you another water saving experiment I've been playing around with.

This is a variation on the wicking beds that are starting to become quite popular (in Australia at least) for growing vegetables in areas where water supply is a problem (i.e. most of Australia!).

The theory is that the plants are grown in some sort of raised bed with a plastic liner in the bottom half that retains water.

The water moves upward through the soil profile through capillary action, creating constant moist soil conditions, and reducing evaporation loss to almost nothing because the plants can access the water before it reaches the surface. The plastic lined sump is filled with gravel or coarse sand and topped up with water by means of a pvc tube inserted into the bed.

In my version the plastic liner (I use plastic sheet membrane for waterproofing concrete slabs - Forticon, or similar) is placed directly into the ground, then I run a length of perforated Ag-Drain in a filter sock along the bottom for the entire length with a pvc up-stand at one or both ends to enable filling and water level checking. The bed is then back-filled with the sand I dug out of the hole, and depending on the situation, sometimes I mound up a foot of top soil over the whole lot.

Here is a small one I dug recently in an existing garden bed:

Plastic liner and Ag-Drain installed:

Back filled and ready to go:

[Jonathan]

Here is a slightly bigger one - you can see how sandy and crappy my soil is - and the need to stop the water moving through it so quickly.

This one was dug between some Livistona decoras and a Bunya Pine that were in need of some water...I'll plant more palms and trees on and around it this spring.

You get the idea!

[Jonathan]

Here is the first one of these beds that I set up last summer, it's been recharged by the winter rains and everything is growing happily.

This one has 8 L. nitida's, a couple of Macrozamia moorei's five Melia azederach and a few Brachychiton bidwillii...and there are two B. rupestre and a Ficus rubiginosa growing on the edge of the bed.

You can probably see that the soil level is mounded up above ground level - that's to ensure that the plants have their fine surface roots out of the wet zone so that they get enough oxygen and dont drown.

You can see the corner of the liner poking out in the foreground - I might get round to cutting that off one day!

In later versions, I've sunk the plastic liner well below ground level, so they can be back filled to natural ground level.

Sorry about the poor light in some of the photo's - it's the middle of winter here and sun the angle is low and mean.

If I lived in California or anywhere else with a dry summer climate like mine, I'd seriously consider giving this system a go.

Cheers,

Jonathan

[Bennz]

Looking good Jonathan I'm curious though, how high up the sides of the trenchs did you bring the plastic? The pictures look like there is very little air gap above the plastic. I envisaged something more like a buried NFT hydroponic system, with a shallow pool buried maybe a foot or so subsurface. Did you dig the trench exactly on contour, or have you allowed variable contours and planted according to water requirements?

Free draining sand soil has some real advantages too! Digging it, for one thing.

[Jonathan]

Yeah - the sides came up a bit high on the first one, but it's not much of a drama, because the worst case scenario would be that you would drive a crowbar through the liner a little further down the side to create some weep holes to lower the water level. On the newer ones I've probably finished the sides 6 inches below ground level and will mound up another foot above that in some, none in others, depending on what I plant in them.

The high water level is producing no problems at all for the plants so far, despite being the coldest winter we've had for a long, long time, and some of those plants - Macrozamia, Brachychiton - are not plants you would normally consider as requiring or even tolerating a high water table. We'll see what happens over the next few years, it might all end badly...

The trenches are roughly on the contour, but due to the rough arsed nature of digging with a front end loader on a small tractor, there is considerable variation in the level of the bottom...so probably more water at one end than another.

If I was more patient I'd probably be a bit more scientific about it!

Cheers,

Jonathan

[Bennz]

Have you got the Brachychiton and Melia actually in the trench or beside it? I'm wondering what the root structure would do planted inside the trench, probably grow super fast then get blown over in a wind in about 5 years!

Are the Melia the var. australasica or the more common Asian genotypes? I've been making a feeble effort to find seed of a strain good var. australasica for years. Earlier colonial reports mention this tree having a dead-straight trunk, over 40m tall and 1.5m trunk diameter! They are weedy at my in-laws place in NE NSW, and nothing like that size. The Aussie form seems to grow faster here than the Asian ones.

Coldest winter in a long time here too. Not enjoying it. At least there are a lot of sunny days and not too muddy.

[Jonathan]

I think it's the Australian Melia...the fruit shape matched, from memory, and every description I've read says they are a small to medium, often shrubby tree.

Stop press - I just found a website saying "The tree can reach height of 12m at maturity and having a width of 6-8m (sometimes up to 30m in its natural environment). The plant has an average lifespan around 20 years"....not sure what that means. does it grow to 30m in 20 years then die? Sounds like a silver wattle!

By the time the trees get big enough to present serious wind resistance their roots should be so intertwined that you would have to blow the whole trench over.

That's my theory and I'm sticking to it until the trees start blowing over!

Cheers,

Jonathan

[Peter Pacific]

Hello Jonathan, this looks great and I have crappy sandy soil too!

My question is what happens when the roots reach the liner? Will they puncture the liner? Grow around it? I have seen this near ponds when you want to create that rain forest look in a dry climate.

Good Luck and keep us apprized as Dave would say.

Peter

[richnorm]

I have thought about doing this myself by simply burying a bucket underneath new plantings that need a lot of additional summer moisture. My concern was that the water would go "sour".

[Jonathan]

Thats kind of how my thought progression started...but it means a lot of buckets!

I wouldn't worry about it going sour - a palm of any reasonable size would drink 10 litres of water before it had time to go sour.

Did you see my photo's in the Nursery Pots with high drain holes thread? Those reclinatas have been sitting in stagnant water for 9 months now, with no trouble at all.

I'm hoping that running the Ag-drain through the bed with a riser at each end will allow a degree of oxygen exchange between the water in the sump and the outside world.

The risers have caps on them during construction so that the drain doesn't fill up with sand, but eventually they will vent caps to allow air movement.

Cheers,

Jonathan

[Jonathan]

Hello Jonathan, this looks great and I have crappy sandy soil too!

My question is what happens when the roots reach the liner? Will they puncture the liner? Grow around it? I have seen this near ponds when you want to create that rain forest look in a dry climate.

Good Luck and keep us apprized as Dave would say.

Peter

Hi Peter,

It's a good question and the answer is I don't really know.

I imagine that eventually some roots will penetrate the liner and water loss will occur, but hopefully by that stage the palms will be well established.

In the long run the presence of the liner will slow water movement through the soil profile to a large degree.

Even in a deteriorated state the liner should theoretically still hold some pockets of water, which is a whole lot better than what I have right now!

Cheers,

Jonathan

[LilikoiLee]

Thank you for all of this helpful information. We live in a hot and dry area of the Big Island of Hawaii but my true loves are from the Rain Forest. We go through a LOT of water. Your system will be invaluable!

Lee

[Tassie_Troy1971]

Jonathan's innovative system really works as i have seen the difference in growth firsthand !