Let's talk compost

In the Garden
Ralph Purkhiser, Purdue University Master Gardener

     One of my favorite chores in the garden has always been screening compost.  I am not quite sure why this brings me such satisfaction, but it is a job with noticeable results.  As organic matter breaks down into compost, the process is rarely even.  Some things break down more rapidly than others.  Some people choose to leave the compost “cooking” until the batch is completely done and the result is a crumbly, dark medium.  However, if you are like me, sometimes I need some compost before the pile is finished, and screening allows me access to some finished compost.
     My sifting equipment is pretty simple.  It consists of a wooden frame with some quarter-inch-weave hardware cloth attached.  My frame is about 12 inches wide and 15 inches long.  It fits nicely onto an old cat litter bucket.  I simply scoop some of the compost into the sifter and work it around until the fine pieces fall into the bucket.  The larger pieces that need to compost longer are left in the sieve, and I dump them into a pile to be added back to a compost bin or pile.
     Actually, the source of the compost I have been sifting lately is a huge pile of wood chips that have been sitting for over a year.  I have been using them for mulch in garden beds, but the bottom of the pile has broken down into compost.  After sifting, I throw the large pieces back onto the mulch pile to use for mulching or to continue to break down.
      My reward for this chore is a bucket of soft, crumbly compost—black gold.  Compost made in this manner has not been turned and allowed to heat to a point that would kill weed seeds and pathogens, so if that is a concern, you may bake the compost at 200 degrees F for about fifteen minutes.  
     There are many uses for the finished compost.  I like to top dress all of my beds with some compost every year.  You do not need to till it in.  The worms will do that for you.  The result is greatly improved soil tilth and a boost in fertilizer.  Your plants will thank you for doing this.
     However, the need for compost recently has been for mixing a growing medium for some new raised beds and some containers.  Buying commercial potting soil was not possible, since I needed a large amount.  I remember that my grandmother never purchased potting soil for her plants.  Instead, she would send some grandchildren out to find a rotten log and dig some of the “wood dirt” that would be the base for her homemade potting mix.
     While we plant directly into the soil in our gardens, we often find that plants grow better when that soil is amended by adding compost, fertilizer and other minerals.  When it comes to planting in pots, most people quickly learn that garden soil is too heavy and that it lacks the good drainage needed for plants to thrive in pots.  Therefore, we buy potting mixes, most of which are “soilless”.  That can get expensive when you use large quantities of potting soil.  To cut costs, many gardeners mix their own potting mix.
     When making the mix I use for general potting, I mix equal parts of peat moss or coir with my screened compost.  I then add about a small amount of fine sand and some perlite or vermiculite, both of which are available at garden centers.  Vermiculite is a mineral, which is mined and then heated to form the particles used in growing mixes.  Perlite is small pieces of volcanic glass.  Both are added to mixes to help with proper moisture control.  
     If I am preparing special mixes, such as mixes for cacti and succulents, mixes for orchids or mixes for seed starting, I adjust my recipe.  I may add small gravel, small chips of bark or other additives.  If you want to make your own mix, I suggest checking with good gardening sites on the internet and experiment until you find a mix that suits your needs.  It may save you some money and it is even fun to do.