What is the Difference Between Hardy and Half-hardy Annuals

The key difference between hardy and half-hardy annuals is that hardy annuals spend their entire life outdoors while, in half-hardy annuals, seed germination takes place indoors, and then the plant later grows outdoors.

An annual plant completes its life cycle in one year. The seed grows to a flower and back to seed, and the plant eventually dies off during this cycle. The main purpose of an annual plant is to produce seeds to ensure the propagation of future plants. They produce flowers that attract insects so that pollination takes place.


1. Overview and Key Difference
2. What are Hardy Annuals
3. What are Half-hardy Annuals
4. Similarities – Hardy and Half-hardy Annuals
5. Hardy vs Half-hardy Annuals in Tabular Form
6. Summary – Hardy vs Half-hardy Annuals

What are Hardy Annuals?

Hardy annuals are plants that grow outdoors or in the external environment throughout their life. From the initial stage where the seed is sown right through to flowering, the plant is fully grown outdoors. Hardy annuals have the ability to withstand stress conditions such as frost without being killed. They will bloom and set the seeds into the next year. But the plant dies and does not carry on to the second year. The seeds are usually sown during late winter or early spring. The sun gains a higher strength during this time and warms the soil, making it easier for the seeds to grow.

Figure 01: Foxglove Flower

Hardy annuals grow better when planted in the ground rather than in a pot or container. This is because the ground allows better insulation for roots, much better than a small amount of soil in a limited space. Hardy annual plants that are exposed and have had time to adjust to colder temperatures will be stronger than plants that are suddenly exposed to cold temperatures. Pansies, foxglove, calendula, larkspur, and sweet alyssum are some common hardy annual plants.

What are Half-hardy Annuals?

Half-hardy annuals are plants where the initial stage of its life has to be in a warm or heated place, and later stage of life is exposed to the external environment. The seeds do not germinate outside, so they have to be sown in a heated place such as greenhouses, propagators, or indoors. The plants are hardened before exposure to the outer environment. Half-hardy annual seeds reject the cold or frozen soil and will not sow until exposed to heated or warm soil. They have a long growing period of the life cycle; therefore, during cold climates, they are planted indoors. This results in plants flowering before the end of cold seasons.

Figure 02:  Baby’s Breath Flowers

Some common half-hardy annual seeds include petunias, cosmos, zinnias, and nasturtium. Half-hardy plants, once grown, may survive a small duration of cold temperatures, but they will eventually get damaged or die if frost or higher temperatures come into contact. A common feature of half-hardy plants is that several varieties of half-hardy plants will decline or wither during summer and re-bloom in the autumn. Some common half-hardy annual plants with flowers are cleome, forget-me-nots, baby’s breath, bells of Ireland, and strawflower.

What are the Similarities Between Hardy and Half-hardy Annuals?

  • Hardy and half-hardy annuals are perennials.
  • If hardy and half-hardy plants are exposed to changing temperatures, they grow stronger.
  • Moreover, they complete their life cycle in one year of time.

What is the Difference Between Hardy and Half-hardy Annuals?

Hardy annual plants grow outdoors throughout their lifetime, while half-hardy annual plants grow indoors during the seed germination phase and later outdoors. Thus, this is the key difference between hardy and half-hardy annuals. Furthermore, hardy annuals are considered perennials that have the ability to survive cold temperatures, unlike half-hardy annuals. So, this is another difference between hardy and half-hardy annuals. Also, flowers of hardy annuals are more glamorous and a little more exotic than half-hardy annual flowers.

The below infographic presents the differences between hardy and half-hardy annuals in tabular form for side by side comparison.

Summary – Hardy vs Half-hardy Annuals

Hardy annuals complete their entire life cycle outdoors. They have the ability to withstand stress conditions such as frost without being killed. Half-hardy annuals cannot withstand cold temperatures. Therefore, they initially grow indoors and later grow outdoors at warm temperatures. This is the key difference between hardy and half-hardy annuals. Hardy annuals are stronger plants than half-hardy annuals. Furthermore, environmental conditions for the growth of the two types of plants also vary between hardy and half-hardy annuals. So, this summarizes the difference between hardy and half-hardy annuals.