What Can I Use Old Potting Soil For?
Every year we all buy big plastic sacks of potting soil to plant up our summer pots and window boxes. But what can we do with it at the end of the season? Can old potting soil be re-used, and if so what for? Read on to find out how to use old potting compost many times!
What is Potting Soil?
Potting soil has been around since the late 1800s and is the kind of soil that is specially suitable for growing plants in pots or other containers. Originally most types of potting soil really did contain “soil” in the form of loam… and this “John Innes” type of potting compost is the kind that many of us grew up using. However, loam is very heavy and unless it is really good quality then it is very prone to compaction, so during the 1980s there was a migration to peat based products. More recently the environmental impact of peat exploitation has been highlighted and so there has been another change of direction to products based around composted bark and re-cycled mushroom compost.
What does Potting Soil Contain?
Whatever kind of potting soil is used the main constituents are broadly similar:
- The main soil matrix – peat, composted bark or other recycled compost material like spent mushroom compost… this makes up the bulk of the potting soil
- Drainage – sand, grit and/or perlite are added to provide drainage and to make sure that the potting soil does not get waterlogged. Roots require moisture but die if the soil is waterlogged and contains no air spaces.
- Nutrients – Organic or artificial fertilizer is added to feed the plants. A “seed compost” will contain very few nutrients, while a “potting compost” will contain much more.
- pH Balancing – Seedlings and plants need a pH balanced medium in which to grow. Some ingredients like peat can be too acidic for many plants so additives like lime are used to create a neutral pH which is better for most plants.
What happens to Potting Soil?
During the growing season the plants use up the nutrients from the potting soil so after a few months the soil becomes exhausted. This is usually rectified by “top dressing” with some new compost part way through the season and by regular liquid feeding. If it is a wet year then the soil in pot can easily become waterlogged… and if it remains like this for any length of time, the potting soil can soon become sour. Some types of growing medium recover very slowly after they have been waterlogged since they can become compacted.
How to Recycle Old Potting Soil:
Here are some simple guidelines that will help you save money by re-using old potting soil and still having success with your plants.
- First remove the old plants… shake the old potting compost into a wheelbarrow and pull out as many of the old roots as you can
- Check carefully for anything living in the soil like worms, grubs, maggots or ants. Get rid of them all… or if the soil is really chock a block with them, it is better to use it for a mulch in the garden or add it to your compost heap.
- Fluff the old potting compost up with your hands and try to incorporate plenty of air into it. If it still seems heavy then add some grit or perlite and give it a good mix.
- Store the old potting compost in the original plastic bag if you can and keep it out of the rain otherwise the compost can quickly get waterlogged.
How to use old Potting Compost:
There are four main ways to use old potting compost: These are listed in order….
- Use it again: In order to use the old potting soil all over again you just need to add some fertilizer of your choice… either normal or organic. The trick here is to just add a small amount since it is very easy to add too much and this will actually damage the roots of your plants and restrict their growth. Literally a couple of tablespoons mixed thoroughly in a bucket load of old compost should be enough. If you like you can also mix it 50/50 with new potting soil to make it go further.
- Use it to grow bulbs: Bulbs do not need a whole load of nutrients since the flower is already fully formed inside the bulb. At the end of the summer the old potting soil is just ideal for planting up pots and tubs of bulbs for spring color
- Use it as a mulch or soil improver: Old potting soil is just great for adding to the vegetable plot in the spring to help improve the soil. Just store it in plastic bags out of the rain until you are ready to use it. It also makes a good mulch in flower borders.
- Use it on the Compost Heap: If the old compost soil is full of worms or grubs… or is just at the end of its life then add it to the compost bin. Keep the sack beside the bin and add a layer on top of the grass cuttings for example.
So typically you can use potting soil at least FOUR times… in the original pot, cleaned up and used again in another pot, used for growing bulbs and then either used as a soil improver or consigned to the compost bin.
So take a Frugal Tip from the MeanyGoat and start recycling your old Potting Soil. When you buy a new sack of compost remember to keep the plastic bag so that you can store it again later. With the rising costs of all gardening consumables, it is really good to be able to use old potting soil several times over!
Here is a link describing how to refresh old potting soil: eHow.com