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Re: [Aroid-l] commercial mixes-Add another factor or two

  • Subject: Re: [Aroid-l] commercial mixes-Add another factor or two
  • From: scottvergara@comcast.net
  • Date: Sun, 18 Dec 2005 12:00:50 -0800

An interesting discussion that has been a pain in the butt or an "opportunity for improvement" for all growers from one person with 5 plants to mega nurseries with 1000's of acres and millions of containers.

The one point that is quite important and not mentioned thus far is what about the container? Many growers use what ever is cheapest and collectors like myself recycle a mix of odd sizes. What needs to be considered is not only the water/"soil" particle interaction but how it acts/interacts in a container of different sizes and more importantly different depths.

Just about any growing mix will work fine if you have a big pile of it on the ground and it is more than a couple feet deep and you plant directly into the pile. This is more like the "real" world. To illustrate my point, one can take the most fertile, well drained garden soil and put it in a pot and the vast majority of the time you will discover that it doesn't "act the same" and many if not most plants that grew well in that soil in the ground, perform poorly or die quickly when grown in that soil in a container. Soil physics comes into play and requires us to at least acknowledge that drain holes (size, number, placement), depth of container, if the container is porous (clay) or impervious, and the surface the pot is sitting on are all part of the system. The latter point has to do with capillary movement of excess water out of the container. As a visual example: water a pot, let it drain for 15 minutes or so, then set it on a paper towel. Typically you will get a great deal more water draining out of the container.

As an aside to this, I used to use the sponge demonstration to explain this point and recently learned a new variation using one of those scrubbing sponges that has a coarse side to it. Essentially take a new sponge and soak it in water. Pick it up and lay it on the dish rack/ cookies cooling rack so that the large flat surface is parallel to the counter top. Some water will drip out. Now rotate it so that it is resting on one of the two longest edges. A bit more water will come out. Now rotate to that it is resting on the shortest edge. Even more water will come out. Now carefully put the sponge, still resting on its shortest edge on a paper towel and see how much more water is removed from the system. Nuff said.

The point of the scrubbing sponge is to make it easier to see what a perched water table looks like and can be seen when the coarse side is on the bottom and the water in the sponge collects along the interface (the bottom of the spongy side and the top of the coarse scrubbing side. This helps to illustrate the myth of putting rocks or broken crockery in the bottom of a container to improve drainage. I always had to roll my eyes when people would mention using rocks, charcoal etc. in the bottom of a container with no holes to provide drainage. And the water went where?

Lastly to add another two factors in that impact water needs in container, namely color of the container and exposure to sun. When I taught greenhouse/nursery management courses one experiment I had students conduct was to measure the soil temperature in containers. They typically never correctly predicted that the soil in a 5 gallon container sitting in the sun in a black plastic pot would register on the SW side, a temperature 1 inch in from the edge and 3 inches down of 130 deg F. Commercial soil pasteurization temperature is 140 deg F. Think about that point for a moment. Most all roots function poorly in water absorption (never mind actual growth) when the soil temps go above 100 deg F. Watering the pot dropped the temperature to around 70 deg F for an hour or so but it was back up over 100 deg F in less than two hours.

There was an excellent one page article in Science perhaps 20 years ago that discusses Soil Physics very nicely and explained the soil/container depth issues, perched water table etc. very succinctly. I couldn't find the copy I had but someone surely has come across it.

Well enough for now. We are expecting a huge freezing rain event with very high winds this afternoon continuing to tomorrow morning which means power outages most likely. This means the weather is moderating after a couple unusually dry weeks of sun and freezing temps that have frozen pots solid and causing significant foliar desiccation. It is kind of odd to be wanting more rain here in the PNW during winter as all we do is complain about it when it falls.

Wishing everyone a Safe, Sane and Joyous Holidaze!

Scott Vergara
Portland Oregon, USA
Zone 8 usually

----- Original Message ----- From: "Ken Mosher" <ken@spatulacity.com>
To: "Discussion of aroids" <aroid-l@gizmoworks.com>
Sent: Saturday, December 17, 2005 9:52 PM
Subject: Re: [Aroid-l] commercial mixes- get real, learn how to grow!

Hi Derek,

What I think I hear you saying is that the soil mix is irrelevant if only the grower will learn what the hell he or she is doing? That seems like a curious comment, and a wrong one. Are you honestly telling me that you can grow Astrophytum asterias in pure peat moss? Well, maybe you could if you wanted to spend an inordinate amount of time "observing" that one plant.

We have been blessed with 1000 different mixes to choose from for a reason. Maybe we could happily get by on 10 rather than 1000, but different plants like different conditions and there's no reason to try to shoehorn the same conditions into every mix.

If I have a nursery pot that's 7" high and the bottom 5" are wet and the top 2" are bone dry, that is bad. If I have tubers planted in it that have not broken the soil yet, how can I observe my plants? And if they are in active growth, shall I wait for them to wilt to water again? I don't think that's a good way to grow a healthy plant. It may survive but I want them to thrive. And how many signals do plants give? Not too many, depends on the plant. The above mentioned Astro. asterias usually gives two signals: I am alive; I am dead. If you manage to catch a condition between the two you can be fairly sure that state 2 is not far off for it will not easily re-attain health.

Or maybe what I was saying in my original post was that the mix I was using gives me NO slack and I want to find one that does. Lots, if possible. I'm a one-guy operation and for better or worse *I* run the hose. I want to become a good commercial grower and in that quest I seek good tools to help.

Lucky for us there are a bunch of people on aroid-l that will give of their expertise.


Derek Burch wrote:
With all due respect to the companies and researchers who have done such valuable work, all that matters is that you learn how to water. If you get that wrong, you can blame the mixes, blame the weather, blame the size pot, but it is you who are to blame if things go wrong. A good commercial grower knows that it is his/her most experienced person who should be holding the hose.

That said, the value of the research work has been in developing mixes that allow us to slack off in our observation of what is going on with the plants, and give us a little slack.

Read your plants, learn how to water and if you only have time to grow six plants properly, don’t try to outdo your neighbour by growing two hundred.

I know, I killed off a bunch of my beloved gingers after switching to a coir-based mix, and not realising what a bear it was to water properly.

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