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. > > > >_______________________________________________ > >pbs mailing list > >pbs@lists.ibiblio.org > >http://pacificbulbsociety.org/list.php > >http://pacificbulbsociety.org/pbswiki/ > > > > >--------------------------------------------------------------------------------------------------- > >Text inserted by Panda GP 2011: > > > > This message has NOT been classified as spam. 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