An introduction to descriptive plant terminology

A simple guide to gardening jargon and an explanation of the terminology used to describe plant lifespans and hardiness.

Many terms are used to characterise the longevity of different plants, and their ability to tolerate certain weather conditions. It can get confusing and can often feel like experienced gardeners are speaking in a secret language. You might find yourself asking “I think I know what annual means, but just exactly how hardy is a half-hardy plant?!”

I am going to break down some of the most-commonly used expressions and explain what each one means. Once you understand the language used, you’ll be less daunted next time you turn a plant label over at the garden centre. It will make your gardening life so much easier.

· · ─────── ·𖥸· ─────── · ·

 

Plant lifespan – annual, biennial or perennial

All plants have a natural lifespan and there are three main terms used to describe a plant’s lifespan. These are "annual", "biennial" and "perennial". You may also hear the word "ephemeral" too.

The humble sunflower lives for only a few months, whilst the banyan tree can grow for hundreds of years. The oldest known, living, individual plant - a Pinus longaeva in California - is estimated to be over four thousand years old!

It is helpful to understand the lifespan of the plant you’d like to grow. It can determine whether it is going to be suitable for you and your garden, in regards to time frame and its maintenance requirements.

“Annual” – Annuals complete their entire life cycle within one growing season. 

This means that in one season, they germinate, grow, flower, set seed and then die – completing their entire life of growth.

• Lifespan: 1 growing season/year
• Replenishment: Replace each year – with seeds, seedlings or plants
• Example: Helianthus annuus (sunflower)

 
“Biennial” – Biennials complete their life cycle within two years.

This means that they grow the first year, and then flower and set seed in their second (final) year. After this they die.

• Lifespan: 2 growing seasons/years
• Replenishment: Replace each year for successional flowering every year (from the second year)
• Example: Digitalis purpurea (foxglove)

 
“Perennial” – Perennials live for three or more years.

This means that they survive all year round – either visibly, as a plant above ground or by dying back to dormant roots, before regrowing the following year. Some require winter protection (learn more about this below).

• Lifespan: 3+ growing seasons/years
• Replenishment: Naturally grows and spreads. Most can be divided and redistributed.
• Example: Verbena bonariensis (purpletop).

 
“Ephemeral” – Ephemerals* complete several life cycles within one growing season.

This means that in one season, they germinate, grow, flower, set seed and then die, many times – multiplying rapidly. This term often refers to ephemeral weeds, such as hairy bittercress, which can be a terror in the garden.

• Lifespan: < 1 growing season/year
• Replenishment: Naturally reproduces rapidly.
• Example: Cardamine hirsute (hairy bittercress)

*I have seen the word, ephemeral, used simply to describe a plant that is “living for a very short time”, particularly in reference to spring ephemerals and desert ephemerals. This tends to be when it is used as an adjective to describe its short lifespan, rather than as a recognised plant category.

 

· · ─────── ·𖥸· ─────── · ·

 

Plant hardiness – hardy, tender or half-hardy

The hardiness of a plant refers to the temperatures that plants can withstand. Generally all plants are categorised as hardy, tender or half-hardy.

In the UK, when we say that a plant is “hardy” we mean that it can tolerate the cold, so my advice below is in reference to living in the UK (where we rarely get winters colder than –10ºC).

“Hardy” – Hardy plants can withstand temperatures down to –15°C. Can be sown in situ.

• Temperature: Minimum –15°C
• Examples:
• Lathyrus odoratus (sweetpea) – “hardy annual”
• Digitalis purpurea (foxglove) – “hardy biennial”
• Verbena bonariensis (purpletop) – “hardy perennial”

Hardy annuals will complete their life cycle within one season and can withstand outdoor winter temperatures down to -15°C. They can be sown outside – the seedlings can happily survive spring frosts down to –5°C. They will take a full year to go from seed-sowing to seed-setting.

Hardy biennials will complete their life cycle within two seasons, and can withstand outdoor winter temperatures down to -15°C. They build up a strong root and leaf system in their first year, so they can survive the average winter and then go on to flower in their second year.

Hardy perennials will live for three or more years, even with freezing ice or snow over the winter. They can withstand outdoor winter temperatures down to -15°C.

·𖥸·

“Tender” – Tender plants cannot survive frost or temperatures below –1°C.

• Temperature: Minimum –1°C
• Examples:
• Impatiens walleriana (busy lizzie) – “tender annual”
• Nicotiana sylvestris (tobacco plant) – “tender biennial” (grown as annuals)
• Canna indica ( canna lily) – “tender perennial”

Tender annuals will complete their life cycle within one season. They are susceptible to death if the temperature drops below 5°C. They need warm soil and air temperature in order to grow well, so it is best to sow these in protection and then place them within your garden after the danger of frost passes (when the soil and air temperatures have warmed up).

Tender biennials will complete their life cycle within two seasons. They are susceptible to death if the temperature drops below 5°C. Tender biennials can be overwintered or treated as half-hardy annuals by sowing seed/planting each year.

Tender perennials will live for three or more years, but are susceptible to damage or death if the temperature drops below 5°C. They need to be overwintered/protected in the UK. Store tender bulbs/tubers/corms in a cool, dry place. Overwinter non-bulbous, tender perennials indoors, as potted plants, or take

·𖥸· 

“Half-hardy” – Half-hardy plants can survive temperatures down to -5°C. They need to be sown in protection and planted when all danger of frost has past.

• Temperature: Minimum –5°C
• Examples:
• Impatiens walleriana (busy lizzie) – “half-hardy annual”
• Nicotiana sylvestris (tobacco plant) – “half-hardy biennial” (grown as annuals)
• Canna indica ( canna lily) – “half-hardy perennial”

NOTE: Half-hardy is a bit of a halfway-house term, often used simply to describe bedding plants which are sown in heat in winter or spring, before being planted outside after danger of frost has passed. It can be a bit confusing, as for example, there is a crossover between tender perennials being treated like, and referred to as half-hardy annuals.

Half-hardy annuals will complete their life cycle within one season. They can be grown outdoors but will require winter protection from frost and temperatures below 0°C. They can tolerate cool soils but will be damaged by frost. Tender biennials can be treated as half-hardy annuals by sowing new seed/growing new plants each year.

Half-hardy biennials will complete their life cycle within two seasons. They can be grown outdoors but will require winter protection from frost and temperatures below 0°C.

Half-hardy perennials will live for three or more years. They can be grown outdoors but will require winter protection from frost and temperatures below 0°C.

· · ─────── ·𖥸· ─────── · ·

 

More perennial plant language

We’re nearly there! Now that I have explained the lifespan and hardiness terms used in everyday gardening language, I wanted to talk about a few more words specific to perennials. Sometimes we are given even more detail when we are told about a specific plant.

You may have heard about a perennial plant being referred to as “woody” or “herbaceous", as well as characteristics such as "evergreen" and "deciduous" being discussed. These words all refer to the way the plant grows and whether or not it retains its leaves throughout the year.

·𖥸·

Evergreen and deciduous

Is your plant evergreen, semi-evergreen or deciduous? Find out below –

“Evergreen” – Evergreen plants retain their leaves all year round.

• Example: Arbutus unedo (strawberry tree)

“Semi-evergreen” – Semi-evergreen plants retain most or some of their leaves all year round.

• Example: Ligustrum japonicum (japanese privet)

“Deciduous” – Deciduous plants shed their leaves each year.

• Example: Cornus alba (dogwood)

Woody and herbaceous perennials

Is your perennial herbaceous or woody? Find out below –

“Herbaceous perennial” – Herbaceous perennials are non-woody perennial plants that die back in the winter and regrow in the spring.

This means that they become dormant and die back to an underground rootstock. They won’t show above ground until the following spring.

• Example: Acanthus spinosus (bear’s breeches)

“Woody perennial” – Woody perennials maintain a live, woody stem at the end of the growing season.

This means that they do not die back completely and they exhibit secondary growth (new growth). This classification includes shrubs and trees.

• Example: Syringa vulgaris (lilac)
  
  

Trees and Shrubs

All woody perennials are classified as either a shrub or a tree* – but do you know the difference? Find out below –

“Shrub” – Shrubs are woody-perennials with multiple stems arising at or near to the ground. Officially a shrub is less than 8 metres tall.

• Example: Buddleja davidii (butterfly bush)

“Tree” – Trees are woody-perennials with a single, main stem or trunk. Trees have lateral branches that emit from the main trunk, usually some distance from the ground and are officially more than 8 metres tall.

This means that they do not die back completely and they exhibit secondary growth (new growth). This classification includes shrubs and trees.

• Example: Quercus robur (oak tree)

*Lianas are also considered to be woody perennials. Lianas are a type of climbing vine generally found throughout tropical rainforests. They are structural parasites of trees as they can reduce the vigour and survival of their hosts

 

· · ─────── ·𖥸· ─────── · ·

 

There are, of course, a lot more plant-based phrases and terms that I could talk about, but I think that’s enough to get started. Let me know if you enjoyed this run-through, and please leave any questions in the comments below.