Reprinted with permission from Herb Gardening from the Ground Up: Everything You Need to Know About Growing Your Favorite Herbs. Copyright © 2012 by Sal Gilbertie and Larry Sheehan. Published by Ten Speed Press, a division of the Crown Publishing Group, Berkeley, CA. The following excerpt can be found on Pages 27 to 32.
Before we consider the first herb garden, let’s analyze the general conditions that determine how individual herbs grow for those herb garden beginners. Each herb’s life cycle, climate requirements, growth pattern, and means of propagation dictate what you can and can’t do for it in the garden. Becoming familiar with these key factors is really more important, at this point, than knowing which names belong to which herbs.
Herbs live according to one of three distinctly different timetables: annual, perennial, or biennial.
An annual is any plant that can be sown from seed and will mature to harvest stage within one growing season. Left outside into winter, both plant and root structure will be killed by freezing temperatures or even a light frost.
Many of our most familiar culinary herbs are annuals–basil, chervil, coriander, dill, summer savory.
A perennial is a plant that comes back every spring. The plant itself may be killed by frost, but the root structure is hardy and, after hibernating for the winter, it sends up new shoots at the start of spring. Mints, sweet marjoram, tarragon, sage, and oregano are all hardy perennials.
Tender perennials such as rosemary, bay, and lemon verbena can with¬stand a frost but not substantial freezing, so for practical purposes they must be either treated as annuals in the garden or brought indoors in pots over the winter months, then returned to the garden in the spring.
A biennial is a plant that takes two years to mature. Its root structure survives the first winter it spends outdoors, but when the plant goes to seed in the second growing season, it has outlived its usefulness. Parsley is the most familiar of the relatively few biennial plants.
Life cycle and climate obviously are interrelated. Because all annuals are killed by frost, they are classified as tender. But some annual herbs are more tender than others. A windy, 40° F night will kill basil but not affect the dill plant right next to it. Both are annuals, but basil is very tender and dill is not.
Most perennials are hardy, but some don’t survive the winter intact because their root structures die in severe cold weather. One of my custom¬ers manages to keep her rosemary alive through the winter only because the plant is located in front of the vent for her clothes dryer, and this particular woman does a lot of laundry.
The other side of the coin is that some perennials, like French tarragon, don’t do well in the absence of a cold winter. In similar fashion, many roses and perennial spring bulbs fail to thrive in southern gardens because the weather doesn’t permit them to go dormant and recoup their energies. Plants in southern gardens also are susceptible to more damage from insects and, due to humidity, fungus.
Sunlight is important to all herbs to varying degrees. Some will tolerate partial shade, but few will really do well in total shade for long. Most herbs, which after all originated in Mediterranean countries, achieve their best growth in full sun. It is the long hours of sunlight that force the herbs to pro¬duce the oils that give them their unique aroma and flavor in the first place.
Rate and Pattern of Growth
Knowing the size, shape, and spreading pattern of each herb is indispensable to a successful garden plan. Think of herb gardening as landscape architec¬ture practiced on a small scale. Each herb must be located to complement its neighbors and not get in each other’s way. Illustrations accompanying this chapter depict the growth patterns, above and below ground, of eight repre¬sentative herb plants.
Perennials must be given more room from the start, because they are per¬manent garden residents which grow larger every year.
Some perennials grow on a single stem, others via an underground net¬work of roots and new shoots. It is the latter–the spreading perennials–that must be watched carefully, and periodically dug up and divided to keep them within bounds. A single mint plant left untended in good growing conditions will spread five feet in every direction within three years.
You must also consider an individual herb’s potential for growing tall or wide, above ground. Herbs such as angelica, lovage, or Jerusalem artichoke, which reach six feet in height, should be located at the back of the garden so they won’t cast shade over shorter plants. Rosemary will grow four feet wide over a period of years if it is provided adequate protection from winter’s rigors. Other herbs may be kept in place by cutting them back periodically.
Some herbs, such as parsley or chive, grow effectively in rows, and others, such as Teucrium (germander) and Santolina, can be trained into low hedges; for example, in formal knot gardens.
Certain herbs have an almost freakish rate of growth. Borage plants will crowd out their neighbors in a matter of weeks in early spring if you haven’t allocated enough space to them. Bee balm and lemon verbena start slowly in the spring but bush out dramatically in summer if left untended.
Means of Propagation
The four proven ways to coax new herbs into life are from seed sown by the gardener, from cuttings of stems or branches, from divisions of root systems, or from seed dropped by the plant itself (self-sowing).
Most annuals are started from seed, a relatively easy method. These herbs can be sown directly into the designated area in the garden or planted as seedlings after having been started from seed in planting pots or trays indoors. This indirect sowing method is useful in northern climates to get a jump on the season.
Some perennials can also be started from seed, but it is easier, with single-stemmed perennials, to take cuttings off an existing healthy plant and place the branch in a sand/perlite mixture. Properly watered and given enough light, this shoot will send out new roots in a short while.
It is even easier to propagate spreading perennials such as those in the mint family. By digging up the root system of an established plant, one can divide the roots into as many new plants as needed.
Finally, there are the herbs that produce their own seed in the course of the growing season and, with a little luck, sow their seed in and around the area of the original plant. Annuals such as dill, and perennials such as oregano or lemon balm, commonly produce these so-called volunteers, which make their appearance in the garden the following spring, and invariably prompt at least one customer a year to run into our garden center declaring, “Sal, my dill’s a perennial!”