Water retained by various soil ingredients

Randall P. Linke randysgarden@gmail.com
Tue, 23 Oct 2012 17:43:32 PDT
I've found perlite to be useful with summer growing bulbs that like
moisture, such as dierama.  I also use it in the lower half of very large,
deep pots as it does contribute to portability and I try to keep it below
the level the bulb itself will be growing, especially if it is summer
dormant.

Happy discovery this evening.  One of my Romulea autumnalis that I thought
lost, then found, rescued and repotted this past summer is sending up a
bud!  I've not seen it bloom for four years.  I will post a picture when it
opens.

Randy
Monterey Bay Region
California

On Tue, Oct 23, 2012 at 12:04 PM, Jane McGary <janemcgary@earthlink.net>wrote:

> Michael Mace reported his experience with potting mixes and water
> retention.
>
> Books on rock and alpine gardening contain a treasury of information
> on soils and soil ingredients. Louise Parsons contributed a long
> chapter on the subject to the book "Rock Garden Design and
> Construction" (Timber Press), which I edited. It includes information
> on both air and moisture availability in various materials.
>
> I never put peat or bark/shavings in a bulb mix. My standard one when
> I grew my bulbs in clay or mesh pots was 2 parts coarse, sharp sand
> (not lowland sand), 1 part horticultural pumice, and 1 part screened
> forest topsoil (from my own woods). Now the bulbs are planted out in
> raised beds, and I have a mixture of clay loam and leaf compost below
> them, and the bulbs themselves are in the same coarse sand (some may
> eventually pull down to the loam) and topped with small gravel mulch.
> The sand is not washed and comes from an upriver quarry, so it has a
> lot of rock fines but virtually no organic silt in it, and a lot of
> grit. It retains some moisture, and using it requires application of
> soluble fertilizer during the growing period.
>
> Anything I put in a pot, including seeds, gets a mix with plenty of
> pumice. I also have been using it to top-dress seed pots the past few
> years. It's a bit more likely to acquire algae than crushed basalt
> grit, but I haven't seen liverwort on it, or even moss except in pots
> more than 3 years old. I also root cuttings in pure pumice, but
> should note that I buy unwashed pumice, which isn't available outside
> this area, I think. As for Perlite, it is mostly useful for
> commercial nurseries where containers and flats have to be lifted a
> lot, and if the other ingredients are not also light in weight (e.g.,
> bark), it will come to the top.
>
> These remarks apply to summer-dormant bulbs. SUmmer-growing bulbs
> such as Lilium or Eucomis can be grown in more organic mixes.
>
> Jane McGary
> Portland, Oregon, USA
>
>
>
> >Hi, gang.
> >
> >
> >
> >It's planting time in California, so I am once again playing around with
> >soil mixes to see if I can find the ideal formula for my potted bulbs.
> >
> >
> >
> >Several years ago I had what I thought was a clever idea.  My usual mix
> >(50-50 sand and peat) made for very heavy pots.  So I decided to
> substitute
> >a lighter-weight ingredient for some of the sand.  Perlite is cheap, and
> >inorganic, so I decided that would be a good substitute.  I potted a lot
> of
> >bulbs in a mix of 50% peat, 25% perlite, and 25% sand.
> >
> >
> >
> >It was a very bad mistake.  I lost a significant number of bulbs to rot,
> and
> >many more looked unhappy.  For a while I thought maybe there was a
> chemical
> >in the perlite that killed some bulbs, but finally I realized that perlite
> >retained a lot more water than I thought it would.  My mix was too wet.
> >
> >
> >
> >Fast forward to today.  Before my next soil experiment, I decided to do a
> >little testing.  So I took equal quantities of six potting ingredients,
> >weighed each one, soaked it in water for six hours, poured off the excess
> >water, and then weighed the ingredient again.  This told me how much water
> >it retained.  Here are the results, with 1 = the amount of water retained
> by
> >sand.
> >
> >
> >
> >Sand                                      1
> >
> >Pumice                                 1.4
> >
> >Redwood compost*       1.95
> >
> >Supersoil**                        2.2
> >
> >Peat moss                           2.46
> >
> >Perlite                                   2.6
> >
> >
> >
> >Yeah, the perlite retained more water than even peat moss.  No wonder I
> lost
> >some bulbs.
> >
> >
> >
> >It looks like pumice may be the ingredient I want.  It's not quite as
> >lightweight as perlite, but it retains a lot less water.  Any thoughts?
> >
> >
> >
> >Mike
> >
> >San Jose, CA
> >
> >
> >
> >*Redwood compost (or redwood soil conditioner) is somewhat-composted
> redwood
> >shavings, a widely-available mulch in California.  Redwood decomposes very
> >slowly, so it makes for a long-lasting addition.
> >
> >
> >
> >**A popular potting mix in California, made of 100% organic material.
> >
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