Which Soil Do I Use?
A common question we get asked at the garden centre is “Which Compost Should I Use?” and what an important question that is! It may be compost for a new planting, soil for a raised bed or improving the soil already in your garden, compost for bedding or ericaceous plants; getting the planting medium right will give your plant the best start in your garden.
Our expert Chris Thorne has written a guide on the different types of soil and additives to improve its performance…
What are the different soils?
Loam a name given to any soil that has been or is growing plants. A rich loam would be high in fibre and nutrients and will grow good strong plants.
Soil is another word for loam. It may have peat as its base, for example in the Fens of Norfolk or on the Somerset sedge levels. Normally though it is formed when rock is shattered by frosts on high ground, and it is washed to lower levels over thousands of years where small grains mix with organic matter. If particles are smaller than 0.002 mm they are said to be of clay. Above 0.02mm and we talk of sandy soil with everything in between being a silt.
Top Soil is the name given to the upper layer of soil containing good amounts of organic matter (also called humous). As you dig down, so you reach subsoil which may be clay, sand, or chalk for example.
Multi-Purpose Compost is just that, and can be used in many different areas, it can also be used for seed sowing (though fine seed might need a specialist seed compost or use a fine sieve). Otherwise, you can have one bag of compost for multiple uses but perhaps feeding and watering requirements will differ from one plant to another.
John Innes Compost is a name for a recipe developed many years ago. Its main feature is that there are different recipes for different types of plants. Seed sowing and cuttings use JI seed. Then there is JI No 1 for pricking out or moving seedlings on and No2 for larger plants like Tomatoes. Woody plants like JI No 3 with the most fertilizer in it. Contrast this where you can use one bag of multipurpose compost.
Ericaceous Compost is used for lime hating plants which is the same thing as acid loving. We use a pH scale where pH7 is neutral pH1 is highly acidic (like battery acid) and ph14 is highly alkaline (like bleach).
Acid loving plants (or lime hating) such as Camellias and Rhododendrons thrive in a pH of 4.5 to 5.5, whereas most other plants enjoy pH6.5 to 7.0. pH testing kits are available to help you sample your soil to find out whereabouts on the scale, your garden is.
Additives to Increase pH / Decrease pH level
Adjusting the pH level of your soil can be difficult and a continuous battle. Lime added to your soil will raise the pH, but in this area the need is usually to lower the pH to allow for lime hating plants to grow successfully. Adding sulphur chips or any type of sulphate fertiliser will lower the pH, e.g., Sulphate of Potash is often used to increase flower formation. Lime in the soil locally will move into the rootzone and neutralize the effects of any application. The answer could be to grow these specific plants in pots where you can more easily control things. In the case of acid loving plants, it would be good to use rainwater since tap water is high in lime (you can see this in the bottom of your kettle!). Most plants are labelled if they need special conditions so you can be sure to put the right plant in the right soil provided you are aware of the type of soil you have.
Peat & Peat Free
For many years gardeners have been relying on peat for best results in their gardens. As far back as 2005 moves were made to reduce the amount of peat that was dug up from the bogs. Much carbon is held here and as it is exposed to oxygen it oxidises and gives off carbon dioxide. Until now the problem has been to find suitable, reliable alternatives. We can now be confident that there are good alternatives available. Peat free composts will need handling differently to peat-based ones. They often contain some bark, and this leads them to become free draining so water can run out of the pot and take nutrients with it. The answer is not to apply more water but to water more frequently.
See Our Peat Free Journey here
Sometimes you can improve the performance of your bagged product. Water storage granules can be mixed into your favourite brand of compost. Starting as a dry crystal they can adsorb many times their own weight in water. They are great for hanging baskets and bedding plants. Be careful where you put the compost later. It can be useful to incorporate spent compost into the garden or to try and reuse the compost for overwintering plants but particularly in the latter case, your winter pansies would be far too wet, and would suffer. Once put into open ground these crystals will be there for a long time so be careful what you do with them after their first use. Having said all that when incorporated into compost, these granules can behave like having an extra storage tank in you compost and work really well in dry situations like hanging baskets.
These are used to maximise the potential of your plants. Given good soil and enough water, a lack of nutrients can be a limiting factor towards successful growing. In pots, roots are restricted. In open soil they can grow seeking out new areas of food. Not so in containers. It is essential to put the food in yourself. Some will be incorporated into compost but will soon run out. There are many types of food available to suit different growers. Regular feeding with liquid feed or once every three months with a controlled release type granule will give you the best results.