FOR many years gardeners have learned that the soil is the thing. And the better the soil is, the better the plants grow. A strong root system results when there is good soil. This type of root system will be the engine that drives any plant's growth.
Gardeners may yawn a bit when they hear about the merits of adding compost to the soil now or especially at planting time. They have come to learn that it is truly wasteful to haul away garden debris like weeds, kitchen waste and autumn foliage. The decayed organic material, the compost, is a rich source of nutrients that adds to the soil's life. And the plants, of course, always benefit.
One thing is important. The compost will have to be sifted first, before it is added to the soil. This process removes some of the heavy clods, unrotted materials and stony bits that would not be great if added to the planting areas. This step is simple to do as garden supply houses sell small plastic screens that fit easily on top of old buckets. Or larger screens can be fashioned with hardware cloth nailed onto old screen doors or lath and placed over garden carts for major planting-soil improvement efforts.
In case there are some doubters among us all, the professionals have taken long looks at the effectiveness of adding organic matter to soil. Richard E. Bir and Dr. Thomas G. Ranney reported on their research at a 1992 meeting of the International Plant Propagators Society (eastern region). The topic was so popular that a summary of their findings appeared in a recent issue of American Nurseryman. The men note that "it is what you think you know -- not what you question -- that gets you into trouble."
Their question: Was it beneficial to add organic matter to soil when planting woody plants? They used pine bark and Canadian sphagnum peat as the soil additives when planting mountain laurel seedlings. The soil additives were spread on top of the planting beds at various depths and tilled in to a depth of eight inches. The researchers wanted to observe the resulting growth.
Their findings? All the soil additives benefited the mountain laurel growth, and those plants that had greater amounts of the organic material worked into the soil had produced significantly more growth. They found that three inches of pine bark is uniformly beneficial to all of the ericaceous plants tested.
But what is most important, they found that each species should be evaluated individually for its needs. They also found that none of the plants tested suffered as a result of organic amendments.
In a somewhat similar test, but not as controlled a study, the same results occurred in an extraordinary garden in Scotland.
On a recent visit to the famous garden, Inverewe, the the former director, Douglas Henderson, was our guide. This remarkable garden near Gairloch is in the Scottish Highlands and in the same latitude as Labrador and Siberia. But because the original planter, Osgood Mackenzie, in 1862 started to establish a windscreen planting of pine trees around the perimeter of the garden, the plantings thrived, warmed by the Gulf Stream to allow an incredible array of near-tropic plants.
Among the gems were the Himalayan blue poppy, giant forget-me-nots from the South Pacific as well as many exotics from South Africa and South America. In the background where the see-throughs occur are the Torridonian mountains.
The garden has an exciting collection of huge rhododendron plants and other ericaceous gems, but it was noticed several years ago that some of these huge specimen plants were waning and looking less than magnificent. The cure? A good heavy mulch of compost around the plants. There was plenty of compost to be had and in a few years' time, the plants righted themselves and were looking their finest. The soil was thinning evidently, and needed the boost the compost provided, at no cost to the garden. This remarkable garden has belonged to the National Trust for Scotland since 1952.
Although the major woody-plant planting season will not begin again until early fall, it does behoove all gardeners to follow actively the premise and make good use of all garden waste for their compost pile. And when planting, forget about that old rule of digging a $5 hole for a $10 plant. Make the planting hole big. The researchers found that the old rules die hard, but their recommendations make good sense.
The bigger the planting holes, the better. For woody plants the newest trend is to dig an area that is 5 to 10 times the width of the root ball. That may sound like a lot of work when planting, but the results will be a shrub or tree that will thrive with a sturdy root system that can endure wind and drought. Proper planting in good soil always pays.