Whether you prefer the giant dinner plate Dahlias or the tiny pom-pom style that grows on stems barely a foot tall, these plants require mostly the same care – at least six to eight hours of full sun per day. Despite the differences in size and style, almost all Dahlias share the same light requirements and growth expectations. If you can’t supply enough light for these plants, you’re generally better off choosing a different flowering plant rather than trying to grow them in shade. However, there are a few dahlia varieties that may be able to deal with reduced light levels. This guide will take you through everything you need to know about how much sunlight dahlia flowers need to thrive in your garden.
Botanical Overview
| Name: | Dahlia, Dinner Plate Dahlia, Mignon Dahlia, Tree Dahlia |
| Scientific Name: | Dahlia spp. |
| Native Range: | Mexico and Guatemala, in certain mountainous regions |
| Growing Zones: | Returns as a perennial in USDA zones 8 through 11, grows only as an annual in zones 3 through 7. Dahlias require frequent watering throughout the season. |
| Flowering Season: | Begins flowering in mid to late summer and doesn’t stop until the first frost. |
The Role of Light in Plant Health and Development
Light is what indirectly feeds the plant, not fertilizers or nutrients found in the soil.
Through the power of photosynthesis, plants like Dahlias use chlorophyll inside their cells to generate sugars just by being exposed to sunlight. This is the plant’s source of energy.
That’s why the precise amount of light desired by the plant is needed, no more and no less. Too little light gives the plant less sugar than it expects, while too much light only damages the tissue and leads to sunscald and dead leaves.
Getting light levels just right is easy for Dahlias because they are not as touchy as other plants when it comes to exposure. Plants can’t simply make more fuel from more sunlight, so extra hours of light or more intense exposure is not always better.
Thankfully, Dahlias prefer full sun and can make the most of extra light without immediately becoming damaged or sunscalded.
Types of Light Explained
When shopping for garden plants or houseplants, you’ll see their light requirements listed on the packaging. While it may be helpful to know that one variety prefers full sun and another full shade, you still need to understand exactly what those conditions mean before planting.
What you think of as partial shade may actually be considered low light or full shade in the gardening world.
- Full Sun: Indicates a plant needs the direct, uninterrupted sun for at least six to eight hours a day. Many plants labeled full sun really need more than eight hours a day, especially to produce flowers or fruit, but Dahlias are happy with at least six hours.
- Mixed/Indirect Light: If there is plenty of light but it’s partially obstructed by minor amounts of shade, it’s mixed or indirect light. The light should be available for at least six hours and maybe direct at some points without damage to the plant. A few species of smaller Dahlias can handle these conditions but with less than stellar growth in most cases.
- Partial Shade: Partial shade contains little to no direct light at any point in the day, but mostly mottled and indirect sunlight. Plants in this category generally only need four to six hours of this light per day and don’t want any direct sun exposure.
- Low Light/Full Shade: The most sun-sensitive plants prefer to stay in full shade and only occasionally receive dappled light through the cover. They will only need four hours or so of mixed light to thrive, or potentially no direct exposure at all.
Dahlia Light Requirements
As long as they get enough light, the plants should grow well because there is little chance of sunscalding in most parts of the country.
Dahlias grown in desert environments may risk too much sun exposure and will need afternoon shade or shade cloth to thrive. These plants prefer six to eight hours of sunlight per day, full sun.
Shade is acceptable in the afternoon, but only if it is partial. Partial afternoon shade is good for hot climates or areas with little rainfall since Dahlias can wilt from being baked during that part of the day.
Planting Dahlias out from under cover like overhanging awnings or trees will ensure enough sun for vigorous and colorful blooming. Open borders and beds are good choices, especially for the smaller varieties that stay below three feet in total height.
Containers can work well if you plant just one or two tubers in a large container. If you can’t give your Dahlias as much light as they want, look for a light-colored wall or other reflective surfaces. Planting them near the reflective surface can help boost the amount of light they receive.
If you’re growing dahlias in an area where temperatures reach 100 degrees F during the day, shade is recommended to keep them from wilting.
Growing Dahlias in Less than Ideal Light Conditions
Dahlias planted in shady areas won’t die out necessarily. They may grow taller than usual, even the tallest varieties, in an attempt to reach more intense light. This is called becoming leggy and often leads to flopping.
Since many larger Dahlia varieties already need staking to hold up the weight of their big flowers, it’s not much of an extra hassle to deal with. Choosing short-growing plants and packing them tightly together can help make up for this extra growth and reduce the need for trimming or staking.
Dahlias that don’t receive enough light will produce fewer flowers and may not flower at all. However, you can always wait until the plant goes dormant in the fall and dig it up for relocation to a sunnier spot. Let the plant go through a season of just foliage if it has already started growing in a shady area since it will still build up energy from the year of growth without flowering.
Varieties with dark-colored, black, or purple foliage and extra small flowers tend to deal with a partial shade much better than tall and large flowering varieties.
Dahlia Light Requirements FAQs:
Do dahlias like sun or shade?
Dahlias love the sun and need as much of it as possible in most climates. In very dry or hot climates, they may want shade for part of the day to keep the soil from drying out.
Can dahlias get too much sun?
Dahlias can get too much direct sun and wilt or become sunscalded as a result.
Light-colored, scarred, and dried-out foliage is a sign of too much light exposure.
Do dahlias prefer morning or afternoon sun?
Morning sun is better for Dahlias because it’s not as drying or intense. Since these plants prefer moist soil, they aren’t big fans of the afternoon sun.
Can dahlias grow well in the shade?
Dahlias can only grow well in partial shade when it’s full sun most of the day. Stick to smaller varieties if you only have partial shade all day.
Do dahlias need light to germinate?
Dahlia seeds are light-sensitive and will sprout best with bright light, humidity, and warmth. They don’t need supplemental lighting until they have sprouted.
Wrapping Up
Dahlias need a steady supply of bright light to bloom, but they don’t want to burn up in the summer either. Consider afternoon shade or an Eastern exposure, so they aren’t baked by the setting sun.
For more, see our in-depth guide to cutting dahlia flowers for a vase or bouquet arrangement.
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