I have been asked to write about potting soil and compost so here goes…When plants are grown in pots, they need a loose soil. This soil has air pockets which lets the roots get watered without water logging them, so delicate roots can develop easily. If you put plants into pots using soil from your garden, they will probably not do well and most probably die. For this reason, when planting pots or even digging up plants from the garden to put in pots, use a good quality potting soil. There are many available. Lift the bag and go for the lightest weight one. Some of them come with a small bit of fertilizer already in the mix though this is not necessary and not good for seedlings. (I do not like to use seeding mixes as they are too fine. A potting mix without fertilizer is good.) Fertilizer can be added to the pots later and should not be used full strength for really small plants. There are organic fertilizers available and it is a good idea to use them for many reasons the least of which is to enable the potting soil to be mixed into your garden soil when it is no longer needed in the pots. This will aerate your soil and add water retention capabilities. A good compost can also be applied to the top of the potting soil, which will introduce flora and fauna into the pot.
I have seen instances where potting soil is left in pots from one year till the next, I think to cut down on the amount of soil needed to fill the pot the next year. I do not think this is a good idea as the potting soil breaks down over one season losing a lot of porosity and eliminating the good drainage ability of potting soil. Just go for the good stuff and your plants will grow much better
Really big pots need a lot of soil but there is a way to plant that decreases the amount needed. I have seen masses of plastic peanuts used. Wow is that a mess when empting the pots! A lot of potshards do not occupy much space and are not needed in any pot. When planting in really big pots, unless you are planting a tree that will stay in the pot for several seasons. Most plants do not need all of the space the pot holds, even tropical trees that will be used for one season. This is the method I have used successfully for years: turn empty pots upside down in the bottom of the pot to occupy space until there is enough room left on top the accommodate the plants to be planted. Use your common sense to make this decision (large plants need deeper space and small plants need shallower space!) and remember that the soil will fall around the pots and roots will be able to grow in this soil.
As for compost, if you open the bag and it smells like anything other than soil; it is not finished and will not add to your soil until it is finished, in fact, it may subtract nutrients from the soil as it continues to break down. Often bagged compost is made from debris from landscapers and contains everything put on any garden or lawn. It should, like potting soil, be loose. Lift the bag. If it is very heavy and feels like a cohesive chunk, do not buy it. Read the label to see what it is made of. If the ingredients are not listed, do not use it. Good compost will aerate the soil, add water retention, flora, fauna and micronutrients to the soil. The best compost is the compost you make. You know what goes into it and can tell when it is done composting. This is a process and most people do not know how easy it is and that it does not have to stink (another column). Given this, my favorite composts are Dr. Earth and Sweet Peet, a mulch that becomes compost, both relatively new to the market both available at Lynch’s in Southampton. For other outlets and more information visit www.sweetpeet.com.
Jeanelle Myers is a professional gardener and consultant, for gardening discussion you can call her at 631-434-5067.