Greenhouse Growing

Spring-Cleaning Our Main Greenhouse

November 2016 greenhouse interior
The usual, end-of-growing-season state of our greenhouse…
With a solid twelve hours of traditionally Mancunian rain forecast from 14:00 hrs yesterday, I thought I’d nip out in the morning and give our still-newish main greenhouse its first ever Spring Clean.

It’s a wet and messy job and, as I usually aim to get it done in February before the germinating season kicks into high gear, also a cold one. But it’s an essential job, too; a mucky greenhouse is an inefficient greenhouse, suffering from reduced rates of photosynthesis and an increased risk of pest and disease problems. Plus, greenhouse cleaning marks one of the key turning-points of the gardening year, from the tail-end of still-winter to the earliest days of pre-spring, so it’s a task I welcome, and attack with gusto.

Here’s how I go about it:

Get Kitted Up

I always wear my oldest, scruffiest, scrattiest work-gear for this job, because I know I’ll end up soaked and stinking of Jeyes Fluid before I’m done. Heavy-duty rubber gloves are a good idea too if, like mine, your hands tends to be prone to chillblains.

Pick Your Poison(s)

The aim of the greenhouse spring clean is to kill things that you don’t want hanging around with all your tender young seedlings: algae, moss, fungal spores, weed seeds, over-wintering pests. Anything that’s likely to cause a problem needs to go. But at the same time, you don’t want to unnecessarily damage nearby plants that might be coming out of winter hibernation and putting up new shoots. For that reason, I use good old Jeyes Fluid inside the greenhouse and Citrox outside.

February 2017 Greenhouse cleaning solutions
Jeyes for Inside Citrox for Outside.

Jeyes is a traditional cocktail of germ-zapping chemicals that will apparently get rid of everything from algae to bird-flu. It’s an evil-looking dark brown colour and it stinks, so you know it means business. You really don’t want this stuff to come into contact with your dormant dahlias or chilli seedlings though, so make sure you’ve removed everything green to a safe distance before you start spraying it around.

Citrox is an organic alternative, a “soluble formulation of bioflavonoids, derived from citrus fruits, [that] has antimicrobial activity against bacteria, fungi and viruses” (according to one study into its possible use as a mouthwash). It won’t damage any plants it comes into contact with, so it’s generally safer to use on the outside of your structure.

Pros and Cons of both: Jeyes is probably more powerful (although I haven’t seen any documentary evidence either way), and is certainly cheaper. 500ml of Citrox cost me £6.49. At the recommended 25ml per litre dilution rate, that’s ten applications (in a 2 litre pressure sprayer) at round about 65p each. Jeyes retails for around £10.92 a litre, but with a dilution rate of only 14ml per 2 litre sprayer, that’s 71 applications per tin, at around 15p each.

On the other hand, Jeyes is most definitely not compatible with organic growing principles, whereas Citrox is. And if you have a bare soil growing bed in the greenhouse, then you’ll need to change out the soil after you’ve sprayed with Jeyes, otherwise I can imagine it doing a fair bit of damage to the soil biota. Then again, Citrox might do that as well. Best best is probably to change the soil out anyhow, just to be sure.

Dilute as Instructed and Spray

I used to use a hand-trigger spray gun to apply the Jeyes fluid. That was a monumental pain in the… well, the hand mainly. This year I invested in the aforementioned 2 litre pressure sprayer (all of £3 from Wilkos) and it made the job a whole lot easier and quicker.

February 2017 pressure spraying
Add chemicals, dilute as instructed, pump, spray. Easy as.

Start with the outside of the greenhouse. First, disconnect any water butts that are hitched up to the greenhouse guttering. A bit of Citrox in the water is no bad thing, but you don’t want to add in the dead and dying algae / moss mix that you’re about to create.

Start at the top of the roof. Spray one panel at a time and work methodically around the structure, ensuring thorough coverage. You’ll want to spray into all the gaps and joints, because that’s where the algae tends to accumulate. Don’t be shy with the spraying. Much better to give the whole structure a thorough drenching than miss a bit and let the muck get an early foothold. I used around 8l of solution on our 8’x10′ greenhouse, so that’s 400ml of the concentrate, in case you’re keeping score.

Scrub Those Nooks and Crannies

An old toothbrush (or two, or three) is your best friend for this stage of the process. They’re great for getting into the guttering and all the fiddly corners to really scrub away at any hard-to-shift gunk and gunge.

February 2017 old toothbrush
Don’t forget to do the back molars… er, I mean, under the ends of the panes of glass.

If you don’t have an old toothbrush to hand, you might get away with using the very end of a scrubbing brush, or a washing-up brush. See what you’ve got that fits.

Don’t rinse everything off just yet though. Leave the Citrox to do its work for a while.

Move Inside, Sweep the Floor

If, like me, you’ve got a concrete slab floor in your greenhouse then now is a really good time to get down on our hands and knees with a hand-brush and sweep up as much of the loose soil and bits of dead plant matter as you can. Your flooring may vary, of course.

February 2017 greenhouse floor sweeping
You’ll be amazed at just how much crud ends up on the greenhouse floor.

What you don’t want to do is leave all that the crud lying around and assume it’ll just wash away later. That just leads to blocked drainage channels, or a puddle of Jeyes-flavoured mud splashing around when you’re trying to get everything rinsed off later on.

Spray, Spray and Spray Again

This is where the pressure sprayer comes in handy again. With a manual spray gun, you have to be quite close to the glass to ensure the solution makes contact. That means you get spray in your face, your hair, your lungs, and the stuff will drip all down your arm when you’re doing the inside roof panels, too. Far better to pump up the pressure, hit the trigger and spray from a safer distance.

If you’re using Jeyes rather than Citrox, make sure you open the doors as wide as they’ll go, and if you have manual ventilation, peg the vents open as well, once you’ve sprayed them. Trust me, you’ll need all the fresh air you can get.

Again, get the old toothbrush out and scrub away at any awkward bits that you can reach. Don’t forget to run it along the underside of any support struts as well, to dislodge the over-wintering slugs.

Tea Break!

A tea / coffee / hot beverage of choice break is mandatory at this point. You’ll need one by now (if only to wash away the taste of Jeyes) and it’s worth leaving the Jeyes / Citrox to do its thing for a while anyhow.

February 2017 tea break time
Gloves off, brew up…

(Personally, I recommend a round or two of toast and jam as well. But you might be on a diet or something. Entirely up to you.)

Hose Down

You should start on the inside this time (for reasons that will become apparent). This year I invested in a variable nozzle-head for the hose and again, it made a big difference. The ‘jet’ setting is almost as good as a pressure washer. Applied to the narrow gaps where the vertical panes meet the eaves in particular, it’s great for blasting out any lurking mats of algae that you can’t quite reach with your trusty toothbrush.

February 2017 hosing down
Blast into all the corners and crevices to make sure you’ve missed nothing.

Admittedly it’s not the most environmentally responsible use of fresh tap-water, but if you have a full water-butt that you can attach the hose to, you might be able get enough water pressure to do the job with rain-water instead.

It’s worth noting: if you’re hosing down flooring flags as well, do those first, otherwise you’ll just splash a load of muck up onto the lower panels that you’ve just hosed down.

When you move to the outside you’ll find that a lot of the gunk you blasted from the joints has been splattered out through the gaps in the structure, which is why you don’t do the outside first. And of course, you could just leave the outside to nature if you have a lot of rain forecast. But then again, getting that pressure jet into the bits you couldn’t quite reach before is a great way to ensure the job is done properly.

Don’t Forget the Staging and Shelving

We use large, plastic shelving units and metal / wooden staging in our greenhouse and that all needs a good cleaning as well. Spray, scrub, rinse as required.

And You’re Done!

That’s it. Job finished. You’ll need to wait a while before piling everything back into your greenhouse, to make sure the Jeyes fumes have dissipated (if applicable) and to give the inside a chance to drip-dry. Overnight, with the doors open, should do the trick.

Get your work gear into the washing machine, get yourself under a hot shower and then get a warming bowl of soup inside you and you can deservedly pat yourself on the back and congratulate yourself on a messy job well done. Your plants will thank you, too.

2 replies on “Spring-Cleaning Our Main Greenhouse”

Hi Darren, I’ve been looking for a guide to cleaning the greenhouse this winter – this guide fits the bill!
I found this very easy to follow, informative and genuinely funny (humour is right up my street).
I’ll try out your choice of chemical/cleaners this year and I can already tell the Wilko spray bottle tip will be life-saving.
Just wanted you to know you’ve helped out a fellow gardener today! Thanks again!

Thank you Michael, I’m very glad you found it helpful.

By the by, I’ve moved away from the Jeyes since I wrote this – I’m an all-Citrox man now. It’s pricier, but I reckon there are more than enough artificial chemical compounds making their way into the soil without adding any more than I absolutely have to… just my take on it, of course.


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