In the midst of summer, it’s a common question. How much does sun exposure affect algae growth?
And like most answers, the correct one might range from a little to a lot. Isn’t that always how it is? Every pond is different in how it responds to sun light and for some ponds sun light exposure is one of the primary issues.
More accurately, large and deep ponds tend to have less of a problem with sun exposure. Small backyard ponds and even large, shallow ponds can be problematic regardless of what other treatments might be used to control algae growth.
Like all plants, algae (in all it’s forms) can thrive with adequate exposure to sunlight. But light isn’t the only thing it needs to grow. Algae must have adequate nutrients in the water to support it, and when this is coupled with sunlight, most algae types can grow very well.
Now before we go bashing sun light as a bad thing, keep in mind that most fish do best with some sun exposure. Also if you have a water garden with desired plants, these need a fair amount of sunlight each day.
What’s right for your pond? Well for koi and fish ponds, usually a few hours a day is fine. All day sun exposure is not. For water gardens, you can expect to up the amount of light to about 4 to 6 hours a day.
For small ponds the most logical and natural way to control sun exposure is to use desirable plants such as lotus or water lilies. These provide a form of shading to the pond and for fish if you have them. These plants also serve double-duty by absorbing the same nutrients that algae would normally feed on. This is why plants would be a preferred method of “shading”.
Keep in mind as well that a few plants here or there, may not be enough. Some pond experts suggest covering up to two-thirds of a pond’s surface area with plants. This may be more than some owners would like to see in a pond, but the choice is yours. If you don’t want to use that many plants, other options include using aquatic pond dyes, or even structural shading.
I’ve recommended in the past that folks with very small ponds actually use a good sized garden or patio umbrella for light control. Other pond owners have planted trees around their pond to block the sun, but remember that it will be important to keep falling leaves and other debris out of the pond on a regular basis.
Large ponds are obviously harder to cover but normally when algae is present in a larger pond, the main culprit is high nutrient loads due to run-off or organic debris build up at the bottom of the pond. The exception to this is very shallow bodies of water that tend to be very problematic with algae issues.
In large ponds that are six feet or less in depth, the best option to control algae growth is a combination of aquatic pond dyes and beneficial bacteria. The dye restricts light penetration in to the pond and limits it’s stimulating effects on the pond bottom. The added shading also helps protect the natural bacterial activity in the pond as well, as some bacteria can be stressed and negatively affected by high temperatures and long running sun exposure.
One final tip for large ponds involves the dosage of pond dye products. While you can follow the suggested dose instructions on the bottle or package, you may want to experiment with the amount of dye you use at one time. Sometimes simply lightly tinting the water is enough to have a positive effect and most folks don’t find a blue looking soup to be very attractive. So one suggestion is to go with the idea that maybe a little bit of dye will go a long way and feel free to experiment a bit on dosage to see what provides a nice balance of appearance and effective algae control.
No matter what size of pond you may have, sun light can be a great blessing to the overall health of the pond. It can also be a strong stimulant to unwanted algae growth if certain conditions exist. Fortunately for you, now you have several options to aid in the cause of sun exposure and algae control, and all of them are relatively inexpensive and safe options to investigate.