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. If it is unsolicited > mail (spam), click on the following link to reclassify it: > http://localhost/Panda/… >---------------------------------------------------------------------------------------------------