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What’s the Best Temperature for My Backyard Pond?

As the seasons change, so does the temperature of a water garden. Pond maintenance is a crucial part of safeguarding the health of the plants and fish that live in it. Plants, flowers and especially goldfish and koi prefer a temperate water temperature around 70 degrees Fahrenheit. However, since pond planning is a yearly endeavor, upkeep should be done at various temperatures year-round.


As the temperatures rise, certain water temperatures must be considered in order to avoid wasting time and putting the water garden’s ecosystem at risk. Look for consistent minimum water temperatures of:

  • 35 degrees for planting irises and marsh marigolds
  • 50 degrees for planting dormant water lilies and other marginals, and starting to feed fish again
  • 70 degrees for new water lilies and other marginals


When the atmosphere outside becomes sunny and hot, care must be taken to protect the fish. Goldfish and koi prefer a cooler range of 68-74 degrees. If the water passes 85 degrees, oxygen depletion can harm or kill the fish. Sound pond planning and landscaping helps the most in maintaining the proper temperature. Consider planting trees or bushes near the water garden, taking into consideration falling leaves and other debris in autumn. Or set up roll-up awnings to provide additional shade. Ponds should get 6-10 hours of sun each day, but more can make it difficult to keep temperatures down.


Cooler temperatures call for pond winterization. At 45 degrees, it is safe to stop feeding the fish. Below 40 degrees but before freezing, move water plants to the bottom or wherever they will be kept during the winter. Remove all dead and decaying bits from the plants before turning off the pond pump.

One of the easiest and wisest investments to make in the maintenance of a pond’s temperature is a pond thermometer. Float the thermometer at least 18 inches below the surface to make it easy to determine water temperature throughout the year. Considerate upkeep of the water garden’s temperature will ensure that the plants and fish will survive for many seasons to come.