Building up your garden beds with “manufactured” soil.

These articles are extracted from the Yuruga Newsletter
Vol 13 No 1
(December 2005).

Lots of people like to build up their garden beds by adding extra soil. This is a very popular approach to gardening, particularly where your original soil is quite poor or if it is poorly drained.

However, there are serious traps for the unwary, so here’s our advice to you ..

Raw material suppliers often sell ‘manufactured’ garden soils, ie blended products made up of a mixture of various components eg sand, loam, compost etc,

Most of these products also contain added fertiliser so as to give your garden a boost.

The biggest problem with these soils is that the fertilisers added to them are designed to suit typical exotic gardens and so they invariably have a phosphorous level which is too high for native plants. It is very common to hear that natives planted in these soils either die or show severe stress and yellowing. So before you buy any garden soils, get a cast-iron guarantee that there is either no added fertiliser, or that any fertiliser added has a phosphorous level of 3% or less.

Many of these garden blends also have added lime or dolomite, to ‘sweeten’ the soil to suit typical exotic gardens. The trouble is that lime and dolomite are alkaline products which raise the pH of the soil, and natives need acid soils. So there is a very real danger that the soil you buy may have a pH which is too high for natives, in which case your natives will either die or do very poorly.

Another problem, of course, is the danger of buying more than you bargained for, and finding you also have serious weeds such as nut grass, or very serious fungal diseases such as the root-rot fungus Phytophthora.

Dumping extra soil on top of hard ground is not a substitute for preparation of your original soil, even though it may sound an attractive way of getting out of a bit of hard yakka. Even if you import additional soil, the soil surface must be loosened so that the roots of your plants will be able to penetrate into the original ground. If you don’t do this, there will be a hard interface between the two soil types, and when the roots hit the original ground they will either stop growing or grow along the interface horizontally. Either way, the plants will have poor roots systems and will be prone to blowing over.

Our advice to our customers is that, for native gardens, there are lots of risks in buying-in extra soil, and in many cases there is really no need. For more information about this subject, see our Yuruga Information Sheet “Soil Preparation“.