Dear Teagan,

Thank you for your question about watering rhododendron, I assume your emitters are drip? As below shrub drip watering systems are best for the Oregon coast because overhead watering increases the risk of fungal disease. 

Please use this formula to decide how long to run the water. One inch of water is 0.68 gallons per square foot.

Young Rhododendron have shallow roots. During their first year they do need to be watered twice a week when no rain is available. Once established, they need one inch of rain per week. To decide if your watering system is adequate, consider how many square feet of garden area you are trying to water and other plants that are near by that will be completing for the same water, Then calculate how many square feet of soil needs to be saturated 1 inch deep using the formula I provided.

As an example, if you are watering with your 2 emitters that run at 1gpm for 20 minutes combined will put out 40 gallons and saturate 27 sq ft at 1 inch or a 5x5 ft sq space, 2 times a week. 

So if the watering system is primarily focused on the young rhododendron, then you only need to water once a week for 20 minutes unless we have unusual excessive heat. If you are not sure if your plant needs water, simply feel the soil with your fingers. If the top inch of soil feels dry, it is time to water. A good covering of mulch will conserve water and reduce the need to water as frequently during the summer months. Be sure to water the plants well in the fall. A thorough soaking just prior to the first hard freeze will help prepare
your plants for the winter.

I hope I answered your question. If you need further assistance, write to us again.

Sincerely,