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Many profiles for plants contain information about the location. There it is then sunny, semi-shady or shady. But what does penumbra actually mean and is there an exact definition for it?

In a nutshell

  • Meaning of penumbra is not well defined
  • Shadow and sun alternate
  • depending on the course of the day
  • Light is reduced by shading


There is no universal definition of penumbra. Therefore, it is not so easy to explain the meaning exactly. Essentially, it is a location that is both sunny and shady at times throughout the day.

The number of hours is not precisely defined. The word partially shaded alone indicates that about half of the (bright) day should be sunny and the other half shaded. So you're talking about 5 to 6 hours of sunshine or shade per day.

plants and partial shade

For plants that prefer semi-shady places, it doesn't matter how long the sun shines. The intensity of the sun's rays is often more decisive for their well-being. Most plants that like to grow in partial shade do not tolerate direct midday sun. This leads to the following damage:

  • brown leaf tips or spots
  • drooping leaves and shoots despite sufficient soil moisture
  • Susceptibility to certain pests (e.g. spider mites)
  • Fading or lightening of the leaves
Too much sun can quickly lead to sunburn in plants that prefer partial shade or light shade, such as rhododendrons.

Too little light also damages the plants and is noticeable through:

  • lack of willingness to bloom
  • disturbed growth
  • withering of the shoots
  • Root rot due to excessive soil moisture

detect penumbra

The semi-shady locations include, for example, places under dense treetops. Due to the constantly changing position of the sun, shade and sun alternate there. However, not only in the course of the day, but also in the course of the year. With deciduous trees, for example, the location can be in full sun in winter due to the fall of leaves in autumn, but this is mitigated by the lower intensity of the sunlight.

Notice: The place under the treetops is often referred to as light shade, since the light conditions change with the wind.

Table leaf (Astilboides tabularis) in partial shade

Walls, hedges or buildings can also create partially shaded areas. If they face south, they block the midday sun from the area behind them. The plants therefore only get the morning and evening sun, which in most cases is completely sufficient.

frequently asked Questions

How can a sunny site be shaded?

There are various possiblities for that. On the one hand, an artificial shade dispenser can be set up. This variant is often used for indoor plants. On the other hand, larger plants that prefer sunny locations can provide smaller shade.

Do plants that prefer partial shade also grow elsewhere?

That depends on the particular plant. Basically, many plants that need to grow in full sun, although they cannot tolerate it, tend to burn their leaves and need more water. In the shade, on the other hand, some plants can shy away from the lack of light and it quickly becomes too humid.

How do the light conditions change over the course of the year?

It should be noted that not only the length of daylight changes. Since the sun is lower in winter than in summer, the shadows cast by buildings or trees also change.

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