The inner life span of plants | Garden Notes


Barbara Faurot

“When a tree dies, plant another in its place.” – Linnaeus

Plants have a predictable lifespan. Virtually every cell, tissue, and organ in a plant ages and eventually dies. This complex process integrates genetic factors and environmental cues to determine a plant’s longevity.

Unlike animals, many plants have “indeterminate growth”—that is, they continue to grow throughout their lives. They have meristems, or bundles of undifferentiated tissue like stem cells, that allow them to grow larger, bud and spread. Of course, that doesn’t mean they’ll live forever, even under perfect conditions.

The inherent characteristics of each plant, including its growth habits and ability to withstand stress, help determine its expected overall lifespan. The plant life cycle refers to the number of growing seasons it takes to complete its journey from seed germination to maturity and finally death.

Understanding the lifetime and life cycle has a number of benefits. It can help determine seasonal and annual trends in the garden. It can help gardeners decide when to replace an aging plant. It’s also useful for determining strategies to deter specific types of weeds.

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Annual plants are the shortest lived plants, completing the life cycle within a year, from seed germination through flowering, seed production and death. Many are self-seeding, such as California poppies (Eschscholzia californica) and meadowfoam (Limnanthes douglasii). If you have more aggressive annual spreaders such as bittercress (Cardamine hirsuta), purslane (Portulaca oleracea) or chickweed (Stellaria media), remove them at the seedling stage before self-sowing.

Some plants like delicate geraniums (Pelargonium spp.) act as perennials in warmer zones, but are considered annuals when killed by winter frost. Gardeners can bring them indoors over the winter to extend their lifespan beyond one season.

Biennials are usually small the first year as they develop leaves and store food. After a cold dormant period, they flower and set seed to complete their life cycle in their second year. The small plants or rosettes of the first year can easily be overlooked, so it helps to ensure they have enough space to accommodate the growth and blooms of the second year.

thimble (digitalis) is a genus in which desirable varieties such as Rusty Foxglove (Digitalis ferruginea) produce tall spikes of small, rust-colored flowers in the second year, which are then gently re-seeded to begin a new two-year cycle.

More productive overseeding such as Foxglove (Digitalis purpurea) produce a flood of new plants from seed. To deter fast-spreading biennials, including weeds such as bull thistle (Cirsium vulgare) or poison hemlock (Conium maculatum), remove flowers before they mature.

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Occasionally, due to drought or extreme temperatures in a growing season, biennials transition from seed germination to seed production. This is called bolting and can occur when biennial plant beginnings are exposed to cold before being planted in the ground.

Perennials generally go into hibernation during cold weather and return year after year with seasonal warming. Most take a few years to become established. Some, like lavender (Lavandula), cistus (cistus) or daphne (Daphne odora) have a relatively short lifespan. After a few years they can become leggy or woody and show less vigor and fewer flowers. Aging plants can become more susceptible to environmental stress and pest infestations. At this stage, a replacement may be a better option than continuing to invest in remedial measures.

Perennial weeds such as Canada thistle (Cirsium arvense) or bindweed (Convolvulus arvensis) are more difficult to control than annuals or biennials because they can reproduce both vegetatively and by seed dispersal. A combination of techniques is most effective, including careful manual removal and the use of inorganic and coarse organic mulches.

Trees and tree-like shrubs follow similar patterns with predictable growth cycles and lifespans. Typically, fast-growing species develop weaker wood, resulting in a shorter lifespan. native bitter cherry (Prunus emarginata) and alien black poplar (populus nigra) are fast-growing with an average expected lifespan of 30 to 50 years depending on conditions. As they age, they can become less resilient.

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In contrast, the Great Basin bristlecone pine, found in the mountains of California, Nevada, and Utah, can live for thousands of years. Its slow growth produces dense wood that helps it adapt to harsh conditions and resist threats.

Of course, ideal conditions can help extend a plant’s life. Environmental factors can play a big role. Biotic influences include fungal or bacterial pathogens, viruses and insect damage. Abiotic factors include drought, fire, flood, mechanical damage, or herbicide drift. Observing these factors can help diagnose equipment problems and determine appropriate responses.

Finally, when a plant dies, there is some silver lining: the ability to continue the cycle by creating wood chips, compost, or a tree stump — or by planting something new.

If you have questions about plant lifespans or life cycles, the Master Gardener Plant Clinic offers live zoom sessions on Thursdays from 12-12pm
2 p.m. to September. Log in or ask a question at extension.wsu.edu/jefferson/gardening-2/plant-clinic.

(Barbara Faurot is a master gardener and trimmer in Jefferson County and works with other volunteers who serve as community gardening and environmental educators.)





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