Should You Apply Fertilizer Before or After Rain?

Over the last few years of writing this blog, we’ve tackled some difficult garden question and we’re well used to the answer “it depends” when it comes to tracking down solutions. We have to admit however that this one is a bit more complicated than most: should you apply fertilizer to your garden before or after it rains?

As it turns out there’s so much to consider—what are you fertilizing with? What kinds of plants are you fertilizing? How much rain is expected? What’s the current condition of your soil? How does your garden or yard drain? So, there’s a lot to consider when we ask the question “should you fertilize before or after rain?” But we’ll do our best to explain it—and as always we’d love some feedback if you know more than we do!

Rain and Fertilizer

Fundamentally, rain and fertilizer interact about how you think they would, in that rain helps dissolve and distribute fertilizer throughout the soil and elsewhere via runoff. The simplicity ends here, however—things get more complex when we start to try and understand how all of this will affect our plants and the environment around us. There are some pros to applying fertilizer before the rain, including the following:

• By applying particulate/granular fertilizer or compost before a light to medium rain, we can make use of the rain to distribute the nutrients throughout the soil. This jump starts the efficacy of the fertilizer and helps our plants take advantage of it more quickly.
• Fertilizing before a rain shower cuts down on the need to till or top dress the soil, saving time and labor if such efforts are not otherwise needed.
• As the weather warms in the spring, fertilizing just before a good rain can help “wake up” our grass and start the growth and greening cycles for our lawns.
• Many commercial fertilizers recommend watering after applying the fertilizer to the soil, so putting fertilizer out just before it rains can save both time and water.

So far so good, right? Well, as with so many things in the world of gardening there are some drawbacks to fertilizing before it rains that we should consider. The cons are just as important as the pros, and there are a few cons to fertilizing ahead of rain:

• Heavy rain can wash away fertilizer, rather than just distributing it through the soil. This is less true for compost but especially likely with particulate or granular fertilizers and liquid fertilizers. This is bad in and of itself, as it robs our plants and lawns of the nutrition we’ve worked so hard to give them. It also creates environmental issues—fertilizer-filled runoff can pollute natural waterways and harm native plants, fish, and wildlife. This can also result in steep fines from government agencies.
• Heavy rains can likewise compact soil, leaving fertilizers trapped on the surface. This limits their efficacy but with a slower releasing fertilizer it can also cause “fertilizer burn” as the fertilizer is concentrated in one place. Too much of anything is bad, and too much fertilizer in one spot can kill grass and other plants.
• Too much fertilizer plus too much rain can stress your plants. Again, too much of a good thing can quickly turn bad, and in this case dumping a large amount of nutrition and a large amount of water on plants all at once can create stress and other health problems for them. This is particular an issue with particulate and granular fertilizers, which are often intended to dissolve and release slowly into the soil.

The Best Time to Apply Fertilizer

So when is the best time to apply fertilizer—before or after it rains? The answer is a resounding “it depends!” If a light rain is expected and your soil is otherwise in good shape, adding some particulate/granular fertilizer is probably a good step. A light to moderate rain will help it distribute into the soil and give your plants what they need. Unless runoff is an issue or a really heavy rain is expected, compost is almost always a safe bet. If a heavy rainstorm is in the forecast, it’s probably best to hold off adding any fertilizer till after it passes. Making good use of fertilizer requires us to get to know our gardens, the space they inhabit, and how rain and water interact with them.

We will almost certainly be revisiting this topic in the future—it’s complex and there’s a lot more to learn. If you have any ideas or thoughts about how to best use fertilizer around rain, please let us know!