Seed Starting Protip: Why You Need to Have a Fan on Your Seedlings

An oscillating fan points at seedlings under a grow light, which tints the plants purple
Tip At-A-Glance
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This single tip can transform your seed starting setup and help you reduce mold, grow strong plants, and reduce your hardening off time! Let's make it breezy!

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Many of us gardeners start our seeds indoors before the growing season begins. The reason we do this is because it’s just too harsh outside for our plants to thrive—and we want to get our tomatoes as soon as possible after the weather warms up! But can too much pampering of our baby seedlings cause harm? YES!

While at first, we’re trying our best to keep out the elements, eventually, we need to shift our seed starting philosophy to trying to replicate the outdoor elements. We have to introduce the same wind, rain, light, and temperature fluctuations to our plants as they’ll see out in the real world. This tough love approach helps prepare them to leave the nest, and typically, we do this right toward the end of the seed starting process (called hardening off). But what if I told you that starting to introduce outside elements—namely wind—early on in the process makes for stronger, healthier, more productive plants? Behold the power of a simple fan!

A smiling brunette woman in glasses holds a large tomato seedling

Why should you have a fan blowing on your seedlings?

A fan helps replicate the same air movement that happens naturally outdoors. This is important for three main reasons:

  1. Your plants have to grow stronger stems and shoots to “stand up” to the winds. This makes for sturdier plants. You can also achieve similar results by gently tapping or shaking your plants regularly, but a fan (in particular, an oscillating fan), does it all the time!
  2. The drying influence of air circulation helps prevent microorganisms (like fungus and mold) from overgrowing in your seedlings. The right balance of microorganisms is awesome for your soil, but an overabundance of the wrong ones can cause diseased or dead plants.
  3. Dramatically reduces hardening off time. Hardening off is about getting plants used to rain, sun, temperature, and light, but wind can be the one thing that really causes the most damage to new seedlings. Not yours though! Since your seedlings have been in the breeze since birth, they know how to hold their own. Just a few days of introducing your seedlings to the outdoors, and you’re ready to plant.

A gif of seedlings moving slightly due to a fan. The seedlings are tinted purple thanks to a grow light above

When do you put a fan on seedlings?

Immediately after seed germination, we begin to run oscillating fans on low over our seedlings. We wait until after germination for two reasons: 1) keeping a warm, moist environment is important for germination of most seeds, and the fans can dry off the soil and cause crusting and 2) it’s just not needed—let’s save energy where we can!

Growfully Protip

About once a day, we turn our fans up to medium (or even high once seedlings are large) for about 15-20 minutes to replicate gusty winds.

How long should you run a fan on your seedlings?

We run our fans during the day, just like our grow lights. Have you ever noticed that after the sun sets, the breeze tends to die down outside? We’re trying to replicate outside conditions, so we let the “wind” inside die down after sunset, too.

And we keep a fan running on our seedlings from after germination all the way until we begin hardening them off (when Mother Nature provides her own fan).

A tray of seedlings sit outside, hardening off and preparing to get planted in the soil

What are the best fans for seedlings?

Whatever you have on hand and can fit in your seed starting spot! A regular oscillating fan set to low and pulled back far enough so every seedling does a little wiggle (it’s really very cute) regularly is plenty.

If you want to invest in something, we really like these personal USB fans. They can run off of a USB cord or battery, they are small enough to clip onto a seed starting shelf, and they oscillate—which can be hard to find in a small fan. And once you are done with seed starting, they are great fans for clipping on strollers, into camping tents, or even taking with you to hot summer activities (like the always-sweltering 4th of July parade!).

Does the fan have to oscillate?

No, a stationary fan will work, but oscillating is just a closer replication to how “real” wind works outdoors. It’s rare for wind to be constantly blowing at the same speed all the time—oscillation replicates the same idea of a summer breeze ebbing and flowing throughout the day.

 

Can a fan help fix leggy seedlings?

Leggy seedlings are most often caused by low light—the plants stretch to try to reach light. For most plants, you can’t “fix” a very leggy seedling (tomatoes and tomatillos are notable exceptions—you can bury their stems when you move up to the next size pot). But if your plant is just a little leggy, move your grow lights closer (they should be within 1-2” of the foliage) or move the plants to a sunnier spot AND pop on a fan on low. The fan won’t fix the legginess, but it can help strengthen the long stem so it’s not such a big deal.

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Cassie is a Certified Master Gardener and the founder of Growfully. She's been gardening organically for over two decades, and she's so excited to answer all the questions you have about gardening!

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Meet Cassie
Meet Your Guide

Hi! My name is Cassie.

I’m a Certified Master Gardener and founder of Growfully. I’ve been gardening organically for over two decades, and I’m so excited to answer all the questions you have about gardening!

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