Experimenting with sand as a medium - flooding cycle

[Kobus Jooste]

I have decided to experiment with course silica sand as a medium, and am wondering about the flooding cycle.  I first wanted to flood for 15 minutes and then stand it to drain for an hour.  Even that seems to be a bit short a dry time now.  Anyone with some suggestions as to how best determine the correct flooding interval?  What is the minumum moisture level that plants can handle in sand?

 

Any thoughts here will be appreciated.

 

[TCLynx]

I expect your plants will be happy enough with quite a long dry time.  I doubt the sand's high surface area is going to really help a lot for your filtration if you are only flooding the bed a few times a day though.

 

I have some gravel beds that I'm only flooding for about 4 minutes every six hours and the plants in them seem to be doing fine though I've only been running that schedule on them for a few weeks but it's been hot and nothing seems especially droopy in those beds as compared to the ones getting flooded each hour.

 

[TCLynx]

I'm thinking of running some different kinds of experiments with sand now myself but they will be for rather different purpose and function from yours.

[Kobus Jooste]

Have fun!

 

The idea with this, and I suppose future sand beds, are that they should be "extra" - with regular gravel beds supplying all the filtration needed to keep the ratios happy.  I'm sure the bed will add some value, but as you said, will not keep it all in balance.  As the water quality was perfect without its addition though, I'm happy just to test it as a medium for growing stuff in, not as a critical part of filtration (It is getting filtered water, thus it is not receiving major amount of solids).

TCLynx said:

I'm thinking of running some different kinds of experiments with sand now myself but they will be for rather different purpose and function from yours.

[TCLynx]

Then I think you will do great with it just flooding it several times a day rather than hourly.

[Kobus Jooste]

OK, so apart from the transplant stress, I have noticed that during the day time, a longer rotation does lead to a bit of wilting with the new recruits.  I have increased the flooding cycles to 9 per 24 hour period to compensate for this.  All the new plants are continuing to grow, with the ones I carefully pulled out of the sand to check showing new root development.  The sand remains loose enough for the plants to be lifted and re-planted without too much damage.  The sand does not compact under the flood and drain cycle at all, partly due to the structure and I think also due to the sloow flood and drain period.  I now have beetroot, onion, some carrots and a strawberry plant in there and none have clocked out yet. I tossed some lettuce seeds in the bin a few days ago, and these were also germinating.  They may have taken a knock though because I got my hands on a few more kilos of sand for free and added this on top, thus burying the seeds perhaps a bit deeper than what they would like.

 

I am really happy with the overall effect.  Even though the water going in looks clean, the water coming out is even clearer, suggesting that some fines may be ending up inside for me to keep an eye on, but overall, the sand remains loose and full of air pockets by the time the next flood period arrives.

[TCLynx]

Have you gotten any worms you could add to it at some point?  Perhaps that could wait for the next step of the experiment though.

[Kobus Jooste]

I only recently got round to adding worms to the gravel beds, and have not found them again scratching around.........Dead or multiplying, don't know yet.  If you look at the sand now, and the water going in, it does not look like it can hold any worms yet, but it is something for the list a couple of months down the line though.

[Richard Wyman]

Hi Kobus,  have you noticed any sand moving into other parts of your system?    You mentioned a slow fill and drain, is this to prevent movement?

[Kobus Jooste]

Richard - I have two plans there - The slow flood and drain is to prevent compaction and the chance for sand getting sucked out of the system, but more importantly, when I made the bottom drains, I used swimming pool filter pipes specially designed to have gaps smaller that the type of sand I'm using, thus I am pretty confident that sand will not get out.  The overflow as well as the bottom drains are made of these pipes.