Every gardener occasionally experiences the sharp disappointment of watching a cherished plant slowly decline. Despite ideal light and moisture, nothing seems to reverse the gradual loss of vigour and the falling leaves. While diseases and insect infestations do their damage quickly—deterioration is obvious and rapid—a slow decline usually points to problems underground in the root zone, where the most important mechanics of plant life take place.
Poor soil quality kills more garden plants and houseplants than any other condition, and understanding a plant's soil preference is important in influencing its growth. Plants have long memories, and thrive best in soil similar to that of their origins. For example, lavender and thyme grow abundantly in dry, sandy soil, which reflects their Mediterranean origins; hemlocks and ferns grow best in moisture-retentive, humusy soil similar to that of their forest ancestry. Growing these plants in your backyard requires thoughtful soil preparation if they're going to thrive.
Special soil mixes are also required for container-grown plants—tender tropical plants grown indoors, and plants in hot, windy conditions on sunny decks and patios—as well as for cuttings and germinating seeds. Good soil structure, which supplies appropriate amounts of water and oxygen, is more important for container-grown plants than the nutrients soil contains, because plants manufacture most of their food through photosynthesis. In fact, seeds and cuttings do best in growing mediums that contain no soil at all. Their immature crowns and root systems are vulnerable to fungal spores and bacteria present in soil-based mixes, and the lush light and moisture conditions seedlings require greatly encourage the growth of diseases such as damping-off.
Myriad commercially packaged soil mixes are readily available, but you can make your own mixes with a few simple, inexpensive ingredients. Below is a list of the ingredients you'll need, and the recipes to cover several kinds of plants and planting circumstances. Print the soil mix recipes and post them over your potting bench. Be precise about the ratios: it will make the difference between a happy plant and a drooping disaster.