Benefits of a Fan in Hydroponics

A common question on hydroponics sites and forums, and especially concerning AeroGarden units, is 'What is the one thing you wish someone had told you starting out?' or 'What is the one thing I should get that isn't included?' and the like.

My answer is always the same: "Get a fan."  Which is, of course, inevitably followed by: "Why?"

Every type of plant commonly grown in hydroponics can benefit from a fan.  Some, of course, receive more benefit than others; I consider it necessary if you're growing lettuce.  It's helpful for flowering/fruiting vegetables.  It's even helpful for herbs, though less so than the other categories.

In the case of herbs and similar plants, the primary benefits are that the constant slight movements can help to strengthen the stems, giving them a sturdier base for their growth.  This can prevent plants from falling over as they grow (almost everyone who's grown the AeroGarden herb kits can attest to how easily dill flops over!)  I have found that it also helps with compact growth, which is particularly ideal in an AG.

There is also simply the benefit of additional airflow.  This can help to prevent fungal issues, like 'damping off', which will destroy affected seedlings.  This is much more common in soil-grown seedlings, but hydroponics aren't necessarily immune.  Other fungus and mold issues as the plants mature can also be prevented or minimized with increased airflow.

For flowering and fruiting vegetables that have so-called 'perfect flowers' (both stigma and antlers are located in the same flower, often incorrectly called "self-pollinating"), in addition to the benefits listed above, a fan blowing on the flowers can help them to pollinate without any additional intervention from you.  Although it's still a good idea to help assure proper pollination (I strongly recommend the Be the Bee wand AeroGarden offers), a fan blowing on them is often enough, or good as a backup.

It is also crucial if your plants are prone to edema.  Edema is caused when the roots are exposed to too much water, while the leaves are unable to evaporate enough off, which causes it to gather in little 'pockets' in the flesh of the leaves.  It's kinda like planty-acne.  Now, there's nothing we can do about the first half of the issue, being hydroponically grown, but we can help with the other side of the equation.  Dropping the humidity can help some, but even moreso, a fan will help.  It increases the rate of evaporation.  It probably won't help the leaves that already have edema, but it should reduce or eliminate further formation.  To be clear, edema is unsightly, but it isn't dangerous, either to the plant nor to the edibility of foliage.

However, the biggest benefit a fan offers, is for lettuce.  As I mentioned above, I consider it a necessary part of a lettuce-growing setup.  

Because lettuce has been bred to have such large leaves, it can struggle to get nutrients all the way to the edges.  This results in thin, limp leaves in general, and often necrotic (dead) and browned edges, which in turn can lead to oddly deformed and curled up leaves, if the edges die when the leaf is not yet full sized.

This is romaine lettuce - the leaves should be very flat, as seen in the bottom left, not curled at the edges.

So why does a fan help?  It seems almost counter-intuitive; if the edges are drying out, how would adding a fan stop that? 

It has to do with something called "transpiration".  Transpiration is a critical part of a plant's circulation and 'breathing'.  Transpiration is the process by which plants take up water from their roots, and transports it throughout the leaves, where it is released from pores called stomata.  (This process is also why seedlings in a mini greenhouse (like AG domes) will form condensation.)  But along with that water come the minerals and nutrients from the roots.  Thus, a fan helps the water to evaporate more quickly, so the plant will suck up water - and thus nutrients - more quickly, and with a stronger internal flow, they are better able to pump it all the way to the edges.  This in turns leads to stronger, healthier, thicker, and thus crisper, leaves, without the brown, dried out edges.

I thought it was ridiculous when someone first told me to try adding a fan to prevent what you see in the above photos.  But, I picked up an inexpensive clip on fan and tried it out.  I was blown away! (Please excuse the horrible pun...)  I have had very little browning edges since, mostly just in tightly heading or exceptionally thick-leaved varieties, or if the fan is blocked from higher growth in between and I forget to switch sides of the Farm the fan is positioned on for a few days.

As you can see, there is still the occasional little spot of browning on older leaves, but nothing comparable to the ones I grew without the fan.  The leaves are also noticeably thicker and crisper, and retain that crispness much better once they have been picked.

I now keep an oscillating fan on all the plants in my growing area, with the clip-on additional directly on my lettuces, and a 16" air bar on my Gardyn.  I keep them on 24/7, though many put them on a timer to match the light cycle without issue.



Update: 
I had a perfect example of the difference sufficient fan-time can make in lettuces in my current grow (spring '22).  I grew Gustav's Salad lettuce from Baker Creek, which is a more 'heading' variety than is really ideal for AeroGarden growing.  I was moving a single fan between three gardens, which is just not enough.  My Gustav's ended up looking like this:

Realizing the issue, I bought a second fan, so it could be on just my lettuce garden.  I picked the stunted outer leaves severely, and continued picking them for the next few days, as well as cutting off some of the necrotic parts on the inner leaves so they could spread out even if they wouldn't get any larger.  Within just ten days with no other changes but increasing fan time from one day out of three to 24/7, the same plant looked like this:

If you look just above my middle finger in this picture, you can still see one of the remaining stunted leaves.  I have had no further issues with stunted and necrotic-edged leaves from it.

* Lots of folk ask if a ceiling fan is sufficient.  Sadly, probably not.  Unless the ceiling fan is strong enough to make the leaves 'dance', it's not strong enough to help.