Plant Hardiness Zones & Lifecycles

Understanding the different lifecycles of the plants you are growing will help you to determine the best time of year to plant. If you wish to save your own seed, it will also help you to know when you can expect the plant to flower and produce seeds. In flowering plants, such as herbs and veggies, the plant life cycle begins with a seed. The seed will sprout and produce a tiny, immature plant called a seedling (so exciting!). The seedling will grow to adulthood and form a mature plant. The mature plant will reproduce by producing flowers and forming new seeds which will begin the next life cycle. There are three general ways a plant lifecycles are expressed ~ annual, biennial, and perennial. 

Annual plants only live for one year: they sprout, grow leaves, flower, set seed, and die all in one growing season. Annuals are only propagated from seed, not from cuttings or divisions, and must be replanted year after year. Examples of annuals are cilantro, fenugreek, dill, borage, lettuce, and lobelia.  To get a full season of growth out of these herbs it is often ideal to start them in early spring by either direct sowing in place or starting them indoors in containers. Most annuals are well suited for container growing. In general they produce shallow root systems, and are not as drought tolerant as some perennials. Some annuals are self-seeders, which means they will return year after year from the ripened seeds they have naturally dropped on the soil. These plants will often germinate in the moisture of the fall rains and overwinter as tiny seedlings, this gives them a great headstart on the season. Self-seeding annuals include german chamomile, calendula, milk thistle, and opium poppy. Seed saving from annuals must be done in the first year after the seeds have ripened (usually in the late-summer or fall).

Biennial plants live for only two years. In the first year they will sprout and grow leaves. During this first year the leaves of biennials will often form low to the ground taking the shape of a basal rosette. In the second year they will then flower, set seed and die. Examples of biennials are mullein, clary sage, evening primrose, foxglove, angelica, onions, and kale. Biennials may be started either in the spring or the fall, and will bloom the following year. Many biennials are tap-rooted and prefer to be direct sown, others do fine started in containers and then transplanted out. Many biennials are self-seeders and will come back year after year. To save seed from a biennial plant you must wait until the end of the second year, after the plant has flowered and the seeds have ripened.

Perennials are plants that live for more than two years. Some perennials are short-lived, while others are long-lived (such as cedar trees which can live for thousands of years!).  Some perennials are herbaceous, which means they die-down for the winter, and regrow from dormant roots each Spring.  Examples of herbaceous perennials are sunchokes, asparagus, bergamot, marshmallow, oregano, and mint. Others are evergreen and keep their leaves through the winter, such as thyme, winter savory, bay, rosemary and lavender. Perennials may often wait to begin to bloom until after the first or second year. They will then continue to bloom and set seed seasonally each year onward. Perennial herbs can be started anytime from early-Spring to Fall, either direct sown or in containers. 

Tender perennial is a term we use to describe the perennial herb and veggie plants that we grow as annuals because they are not hardy to our region. Examples of tender perennials are tomatoes, lemongrass, basil, lemon verbena, cardamom, vietnamese coriander, and pineapple sage. These plants cannot withstand the minimum temperatures of our cooler winters.  Depending on your which USDA Hardiness Zone you live in they will either need to be overwintered with protection (greenhouse, mulch, row cover), brought indoors, or restarted from seed in the spring. 

The Plant Hardiness Zone you live in will determine which plants will be classified as tender perennials in your region. At our farm on Vancouver Island we are considered to be Zone 8-9. The Plant Hardiness Zone describes minimum temperatures only, and does not factor in other variables such moisture levels, insulating snow, or damaging winds. At our farm we have had years where we have successfully overwintered plants from Zone 10 without protection, whereas occasionally an exceptionally cold winter has damaged some of the more hardy plants from our zone. Working with nature you have to learn to adapt (be flexible and go with the flow!), each year is different, and experimenting and finding what works in your own special microclimate is half the fun.

You can find more info on the Hardiness Zones for Canada here: planthardiness.gc.ca and for the US here: planthardiness.ars.usda.gov