You know these plants: rhododendron, azalea, pieris, mountain laurel and, of course, heather and heath. Add blueberry, huckleberry and lingonberry, and you have a grouping that can provide months of good eating, flowers almost year round, and attractive stems or leaves.
In Britain, such plants are among those that dwell in so-called "peat gardens," in which the soil is amended with enormous quantities of peat. Peat provides the extreme acidity, low fertility, consistent moisture and aeration in which these plants thrive.
All that peat is not a must for a heath bed. But some special soil preparation is required, and anytime you can work the soil is a good time to do it.
SAWDUST IN THE SOIL
Many years ago, in autumn, I prepared a heath bed by mixing sawdust instead of peat into the soil. Any kind of sawdust will do, except that from wood that has been treated with a preservative, such as pressure treated wood.
Sawdust breaks down slowly so provides a long-lasting source of humus, and it is finely divided, so it can be mixed intimately with the soil. It also acidifies the soil, at least for a while.
Soil acidity is crucial for most heath plants, their preference being a range from 4 to 5.5, which is much more acidic than most other plants demand. The ideal is to test your soil and then add sulfur — a natural mineral — to bring acidity to the correct range.
In sandy soils, add 0.3 kilograms (three-quarters of a pound) of sulfur per 9.3 square metres (100 square feet) for each pH unit above 4.5. Use three times that amount for soils high in clay.
Sawdust has just a smidgen of nitrogen, and when soil microorganisms start making sawdust into humus, they're going to need more. As they scavenge excess nitrogen from the soil, plants are apt to get starved for this element. Avert the problem by adding extra nitrogen to the soil along with the sawdust, to the tune of 0.9 kilograms (2 pounds) of actual nitrogen for every 40 bushels of sawdust.
That 0.9 kg of nitrogen might be supplied, for example, by nine kg of any fertilizer that is 10 per cent nitrogen, or by 13.5 kg of — my preference — soybean meal, which is seven per cent nitrogen.
SAWDUST, OR SOMETHING ELSE, ON THE GROUND
To prepare the bed for planting, I spread a 7.5-cm depth of sawdust on the soil along with the fertilizer and sulfur, then dug it into the top 15 centimetres of soil. No need to mix the stuff any deeper because another quirk of the heath family is that the plants have few roots ranging deeper than 15 centimetres.
This is a one-time digging, needed only to prepare the ground for planting.
The bed was ready for planting the spring after the autumn soil preparation. (I could also have prepared and planted that same spring.) For best growth, peat moss is needed at planting time, in the form of a bucketful mixed into the soil of each planting hole.
After planting, more sawdust is needed, or shredded leaves, wood chips, pine needles or any other weed-free organic material, spread five to 7.5 centimetres deep on top of the ground.
Mulch, which needs to be renewed annually, protects the shallow roots from hot sun and drying out, snuffs out weeds, and gradually breaks down to keep enriching the soil with humus.
The only other item in this prescription for a heath bed is water. Plants need a weekly soaking throughout their first and second growing seasons.
When planting a heath bed, there's no need to ban non-relatives. Call it a "peat garden," and trilliums, some kinds of phlox and lilies, and primulas, which also enjoy these soil conditions, will also feel welcome.