Hi All, This is my first post. I'm conducting a container experiment, but I'm uncertain of how to derive the ratio of soil & perlite mixture required for a 1.6 gal or 600 series pot? I've determined my bulk and particle density, respectively, but not really sure how to use these values. Thanks.
Container gardening, particularly with perennials, has very different needs from the considerations we have in the garden. A peat mix will be fine for use over one season with annuals, but as soon as you are considering going beyond one season with the same mix you have to be concerned with the collapse of the peat and compost, and how that impacts drainage and aeration. There is a very good forum on GardenWeb that deals with containerized gardening and once you start going through the posts you will find a lot of commonly held beliefs will be dispelled. Soil, as in garden soil, should NEVER be used in a pot. The best mixes will rely on bark fines as the major component as these break down much slower than peat and maintain proper drainage and aeration much better and longer. You will find several posts there that provide excellent suggestions for potting medium mixes that have been proven performers by scores of gardeners over the years. If you want to conduct an experiment by trying different ratios and mixes, knock yourself out. Experiments can be rewarding. Or save yourself the time and trouble and go with what has been proven to work reliably and use one the mixes recommended on the forum.
Bulk and partcle density http://soil.gsfc.nasa.gov/pvg/pd3.htm really have no bearing on determining the relationship of the types of particles within the soil mixture being measured. That relationship is determined by the amount of each element that is used to create the soil mixture. For example, using measurements based upon a dry volume, such as a cup or a pint or a quart and using the elements perlite, peat moss, decomposed bark product (such as Supersoil) and medium grade gravel (1/4 inch or 3.36 mm or #6 mesh) http://www.sigmaaldrich.com/chemist...chnical-library/particle-size-conversion.html using 1 cup of each would give you a 25% perlite mixture or a 25% sphagnum mixture, or a 25% decomposed bark mixture or a 25% medium gravel mixture. What you are aiming for is to recognize that it is the number of cups or as per the definition of bulk density and particle density, the number of cubic centimeters found in the 600 series pot that are of importance. Therefore you need to make up a test mixture of the potting soil and weigh one cubic centimeter of the blended soil mix. That will equal so many grams of weight which indicates the bulk density. Then following the formula compress the cubic centimeter to see how much empty space there is. In the illustration on the first link it is shown at 1/2. Measure that quantity and plug everything into the equation to determine your Particle density. By varying the relative percentages of the ingredients of the soil mix you can assess both Bulk density and determine Particle density accordingly.
