How Does Light Affect Streptocarpus?

Streptocarpus are becoming popular houseplants and for good reason. They are relatively easy to grow, they don’t need high light and they bloom all year long in the right conditions.

How much light do they need?

Light Requirements for Streptocarpus

The common advice when I started growing streptocarpus (streps) was to provide the same amount of light as for African violets. That did not help a lot because I never grew African violets – that was my mom’s thing. The consensus was that they liked fairly low light and no direct sun exposure.

Purdue University confirms that streptocarpus prefers more light than African violets.

Streptocarpus will grow in lower light, but they grow better and bloom more in higher light. But what is the ideal level? That is not really clear and I have found no scientific studies looking at this.

Here are some rules to use.

• If they are not flowering, give them more light.
• If the leaves are burning, reduce the light. This will probably only happen in direct sunlight.
• They can take direct sun. They don’t do well with a lot of sun outside, but a bit through a window won’t harm them.
• They will flower at 2,500 lux producing leaves that are thin and large.
• They flower better at 16,000 lux. Their leaves will be smaller and have more texture (i.e. more bumps)

The experiments below provide details about some experiments I have carried out to confirm these growing conditions.

Casual Observations

I have been growing streps under lights for several years and use proper LED grow lights that can put out a lot of light. Some of my lights include BESTVA 4000, Spider Farmer SE3000, and Vevor 200, although these are turned down from their maximum output. The following observations are for a variety of complex hybrids including my cultivars.

The lights are about 2 feet above the plants but the overflow plants are farther away from the light, or even on the floor of the plant room, as pictured below. They receive between 2,500 and 16,000 lux, with most of the plants receiving around 6,000 lux.

At 2,500 lux the leaves are larger, thinner, and flat. The surface is quite smooth with little texture except for the veins. The edges of the leaves are also smooth.

At 16,000 lux the leaves grow quite differently. They are shorter and tougher. The surface becomes quite bumpy and textured. The edges undulate and the leaves start to curl under themselves.

Experiment #1: Effect of Light Intensity on Leaves

To test the effect of light intensity on leaves I took two numbered seedlings and divided each into equal-sized plants. Each was potted in my standard media which is about 40% perlite and 60% Promix (peat-based media). This report describes the leaves of one of the seedlings.

One of each plant was placed in low light (2,500 lux) and the other in high light (16,000). The light was mostly from the same source. The high light was right under the center of a Spider Farmer SE3000, about 2 feet from the light. The low-light plants were placed on the floor beside the normal tray of plants. The ones on the floor did get a small amount of light from LED shop lights on the ceiling.

Low light produces leaves that are thinner, larger, and less textured both on the surface and along the edge of the leaf. High light produces thicker leaves with a lot more texture.

Although not evident from these pictures, leaves grown in high light also curl more.

Flower coloration can also be affected by the light level.

Growing Streptocarpus

Other resources for growing streptocarpus:

Article: An Introduction to Streptocarpus

Article: How Does Light Affect Streptocarpus?

Article: Streptocarpus Myths

Collection of my videos about growing streptocarpus