Leftover potting soil can look a bit spent after a year or two, but experts agree that it still has life-giving potential, especially if you take the time to condition it properly.
Once you learn the basics of healthy soil, you'll be able to refresh your old potting soil and save a lot of money by doing so.
Potting soil is technically not soil at all. It is a sterile mix of filler ingredients and organic matter. Some manufacturers may add some starter fertilizer.
Most bagged potting soil mixes contain a lot of cheap pine bark. You may notice that the soil level in the pots has dropped over the season due to the pine bark breaking down.
If you noticed the water was pouring straight through the old soil in the pots, the soil has become water repellent. It has lost the ability to absorb and hold the water that the plants will need for good, healthy growth.
Old soil can become compacted over time.
It may harbor weed seeds and insects from its past residents if leftover from past occupants.
The salts may have accumulated in the soil and on the pots forming a white ring.
The nutrients have probably been flushed out over repeated waterings.
The Goal: Rich soil that smells earthy
The goal is to create a potting soil that is:
- Free of weeds and disease.
- Aerated so the plants can get oxygen from the soil.
- Light enough to allow water (and the air) to flow through the soil easily, yet be firm enough to support the plant.
- Be able to retain the water without draining through too fast.
- Be able to retain the nutrients that you add.
Types of soil amendments.
Garden Soil (Not Top Soil)
Garden soil refers to the loamy soils sold in most garden centers. It is mixed to incorporate a variety of soils and textures and usually targets right on the label a certain type of garden or plant.
- It's sterile, so you can avoid disease, insects and weed problems.
- It's a far better choice for potting soil recipes over Top Soil because Garden Soil is made to mix with fertilizer and organic matter where Top Soil is not.
Side NoteNever add soil from your garden. It is un-sterilized and may harbor disease, insects and weed seeds which can cause future problems such as dead, deformed or stunted seedlings or plants.
A mixture that consists of various decayed plants and vegetative waste is added to the soil to help plants grow.
- It will suppress disease.
- It retains minerals.
- It provides moisture and plant food.
- It improves the structure of the soil.
- It adds several macro and micronutrients to the soil along with several trace elements.
- The compost will be more alkaline and is the better choice instead of Peat Moss for Boxwoods, Hydrangeas, Lavender, and Thyme.
Coconut Peat, Peat Moss, and Sphagnum Peat Moss.
These are types of Peat generally added to potting soils. Here are some of the advantages:
- Peats are highly absorbent material.
- Peats retain water well.
- Peats are a sterile medium.
- Each type of Peat is listed below with the advantages and disadvantages of each.
This is a by-product of the coconut processing industry. It's the finer product that's left behind in processing.
- Coconut Peat doesn't break down as quickly as Peat Moss does.
- It's a renewable resource, unlike Peat Moss.
- It lasts much longer in your soil than Peat Moss.
- It has a more neutral pH than Peat Moss and is good for flowering and fruiting plants that prefer a neutral pH.
Peat Moss/Sphagnum Peat Moss
These are the dead fibrous materials that form when mosses and other living material decompose in peat bogs. Both come in convenient dry, light-weight compact blocks and can be found at garden centers.
- It has an acid pH and is ideal for acid-loving plants such as blueberries, camellias, hostas, etc.
- It is composed mostly of moss, and since the process of decomposition is so slow, it is not considered a renewable resource.
- It tends to become water repellent as its moisture content drops to below 30%.
- It compacts quickly.