To Swale or Not to Swale

I have very thin soil lying on top of bedrock.  During the summer months, it's bony dry.  During rainy weather, and when it rains here it *really* rains, the soil gets totally waterlogged to the extent that this year we actually lost young fruit trees due to waterlogging.  I'd been thinking of adding some fish-scale swales around the fruit trees to help keep the soil moist during the summer and to encourage the soil to build up, but after losing trees to waterlogging I'm having second thoughts.  Would I be better off not swaling but just adding as much mulch as humanly possible to build the soil as fast as possible?  I'm sure swaling would help during the summer, but it might be counterproductive if the swales hold more water for longer during rains and we lose more due to waterlogging. 

Thoughts anyone? 

How big are the trees? Specifically can you move them? In poor conditions building a mound and planting on that will ensure that you can take steps to fix trees. If you are very confident you can actually dig under a tree and use a car jack to raise it then pile in sandy soil beneath it. Combine raising it above the highest water table and some swales to get more rain into the ground and you have a recipe for better fruit.

Two problems with that - first, what to build a mound with (there's no spare soil around!) and second, more importantly, if the trees are on mounds then they aren't going to get through our bone dry summers.  I water them during dry weather to help get them established, but if they're on mounds surely they'll need far more watering and for many years to come?  I've experimented with raised beds here and though they work well for around 7 months of the year, as soon as the dry season starts then we just don't seem to be able to keep enough water in them to keep any plants alive.  It's as though all the surrounding soil just sucks it out like blotting paper. 

The trees are all young, and anything that didn't make it over this winter is going to be replaced with something that can take waterlogged conditions better, like elder (any other suggestions welcome).  I figure anything that survived this year's rain should be able to cope next year, but in some places it seemed as though water was flowing underground and coming up in places we didn't expect a week or so after the rain stopped, and all the trees in those places didn't make it. 

Sorry I'm waffling and having a decision crisis - just bombard me with ideas till I've figured it out...

Instead of putting the swales on contour can you angle them slightly to direct the water in the wet time of the year to a low area?  A pond or series of ponds may allow you to keep the orchard from gettting too waterlogged during the rainy season, and then allow for irrigation when you need it in the dry times.

With bedrock that close to the surface, you probably won't be able to excavate much, but if there is enough slope you can always build up and seal it.

g'day burra,

sounds like you should planting trees in a raised planting system you know create something of a mound then plant each tree.  we have yard that is like concrete in the dry and boggy after big rains makes life interesting but raised gardens and tree plantings works. so our gardens and tree planting areas act like swales with the mulch around them.

with swales as you still need to store water in your soil, think away from the classic copy book trench berm swale and rip some swale lines in less obtrusive and they allow for the water to get down into the sub soil better than does the trench swale. of course with the trench/berm system you create a raised planting position don't you? just be sure you get the trench all but perfectly level or you will create a damming effect and the water will want to escape.

len

It's alright to waffle, it is a big choice to be made. but lets look at it this way, you have two forces that are trying to kill your trees. You have drought, which you can fix with additional water, swales to help raise your water table, amending organic matter in to your soil, mulching, etc.; and you have waterlogging, which will kill your trees, there is no emergency measure that can be done to save them, and any step you take (aside from watering when it is dry) to fix the drought problem will only make the waterlogging problem worse. I suggested sandy soil because it has a lot of voids in it, which can hold air and water. Mix good compost, a little clay, and some sand together and you have a loam that can take and hold water, but will drain away the excess allowing for some air to the roots.

Additionally the roots of your tree will reach down farther than the roots of your raised bed veggies, your tree will still have roots where they are now, it will just also have roots up out of harms way when it comes time for rain.

the idea for creating raised positions for trees is to have the feeder roots in a well drained strat and yes with drough times like we have it makes it a fine balance as to how high the mound should be, the deeper roots are by and largley unaffected by variable extremes of moisture, water logging as we have found here.

also we don't know if there is any slope on this ground mentioned or is it flat and at the bottom of a major run off like hills etc.,?

len

The land is very gently sloping, and what seems to be happening is that during periods of very heavy rain the water is flowing underground and forming a lens and rising to the surface under some of the trees.  Most winters the rain lasts for a couple of weeks at a time, then goes away giving the soil time to 'breathe' a little, then the rains come back a few times, but this winter the rain seemed almost continuous.  Because the soil is so shallow, there isn't much scope for getting it to sink in any deeper.  The trees aren't planted very deeply as it's just not possible, so I'm wondering if I mulch like crazy with whatever I can find them maybe the trees will out more roots higher up?  Or is that just wishful thinking?

Keep the ideas coming - I'm starting to get my head around it all.  I think...

g'day burra,

probably in a damned if you do damned if you don't situation but yes by all means build up the mulch over the feeder roots to create higher medium, keep away from the trunks by at least 4"s and go out beyond the drip line about a foot at least.

when we planted our citrus in raised position we then mulched to around 12"s high this has broken down and been remulched over the 4 years causing no dramas to the plants. i would still consider rip swales along (you could plant into the rip line)with raised position planting. rememeber when creating a mound be it 6"s high or 2 feet high tamp it down as you consruct it to minimise settling, or 6"s might end up 3"s. still dig a hole into the original soils and back fill with amended you can mix with what you dig out if you like, also tamp it down. amendment can be old potting mix whatever is cheap enough. if planting in the dry peiod give the hole amendment a good watering. i prefer to add fertilisers/manures if you go that way on the surface of the mound under the mulch.

over here w use gypsum in the hole and on the surface as our clays are responsive, often throw in a bit of dolomite in case their is some acidity.

len

i think also i would plant them in a raised position so they will drain well, but add a ton of  organic material to  both the soil and as  a mulch on top of the soil that will hold moisture when you get those droughty times..

the standing in water is more likely to be a killer than the drought..esp if you have a good mulch and a good organic soil