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Key takeaways
- Gutters protect the foundation as much as they collect water. Roof runoff pooling at the base rots timber, rusts steel and undermines gravel pads.
- Check first whether your greenhouse kit offers matching gutters. They fit the frame profile better than generic gutters.
- A diverter sends water to the barrel until it's full, then back down the downspout, which prevents overflow at the base.
- Size the barrel to your roof. Each inch of rain on each square foot of roof yields roughly 0.62 gallons.
- Drain and disconnect before hard freezes. Ice can split barrels, diverters and fittings.
Quick picks
- Best first option: matching gutters from your greenhouse manufacturer, if your model has them.
- Best generic gutter for lean-tos and larger houses: a vinyl gutter system such as Amerimax or Raingo.
- Best for small greenhouses and sheds: a mini gutter kit.
- Best diverter: the Fiskars DiverterPro kit.
- Best budget diverter: EarthMinded's rain barrel diverter kit.
- Best compact barrel: the Good Ideas Rain Wizard.
- Best barrel with a built-in stand and screen: the FCMP Outdoor rain catcher line.
- Best for tight spaces: a collapsible rain barrel.
Why a greenhouse needs gutters
Greenhouse roofs are smooth and steep. Almost everything that falls on them runs straight off the eaves and lands in a line right along the base. Over a season, that drip line erodes gravel, splashes soil onto the glazing, keeps timber bases wet, and can wash out the ground around anchors. Our greenhouse foundation guide explains why drainage is the part most builds underdo.
Gutters fix that and give you a second benefit: a supply of rainwater right next to where you use it. Many growers prefer rainwater for plants that don't like hard tap water. Our greenhouse water quality guide covers pH and EC if you want to test it.
How much water can you collect?
The math is simple and worth doing before you buy a barrel.
The 0.623 figure is the volume of one inch of water over one square foot, in gallons. Use the roof's footprint (the ground area it covers), not the sloped surface area. Only the side or sides with gutters count.
Worked example: An 8x12 greenhouse with gutters on both long sides has a footprint of 96 sq ft. One inch of rain gives roughly 96 × 0.623, or about 60 gallons. A single standard rain barrel would fill in one moderate storm. If you want to capture more, link two barrels or use a larger tank.
Smaller example: A 6x8 greenhouse with a gutter on one side only collects from half the roof, 24 sq ft. One inch of rain yields about 15 gallons.
Gutter options
Manufacturer gutters
Some greenhouse kits include gutters built into the eave, and some brands sell gutters as an accessory. Palram - Canopia, for example, has models listed with built-in gutters at major home centers. A matching gutter fits the frame profile and usually includes a downspout outlet in the right place. Check your model's accessory list before buying anything generic.
Vinyl gutter systems
For lean-to greenhouses, larger freestanding houses and anything with a timber fascia, a standard vinyl gutter system works well. Amerimax and Raingo sell vinyl gutter parts at home centers: gutter lengths, end caps, outlets, hangers and downspouts. You'll need something solid to screw hangers into, so this suits wood-framed or fascia-equipped houses better than bare aluminum kits.
Mini gutter kits
Mini gutter kits are sized for sheds, playhouses and small greenhouses. They're lighter, easier to fit to small eaves, and come with brackets that can often be adapted to aluminum frames with clamps or self-tapping screws. Check whether fastening will void your greenhouse warranty or pierce glazing.
The picks
Vinyl gutter system (Amerimax or Raingo)
$–$$Vinyl gutters from Amerimax and Raingo are sold by the part at most home centers, so you can build exactly the run you need. They don't rust, they cut with a saw, and replacement parts are easy to find. Pitch the run slightly toward the outlet so water doesn't sit.
Why we like it
- Easy to find parts
- Rust-proof
- Cuts to any length
Keep in mind
- Needs solid fascia or brackets
- Can crack in hard freezes
Mini gutter kit for sheds and greenhouses
$Mini gutter kits come as a complete set with gutter, end caps, brackets and a short downspout. They suit small hobby houses and cold frames and look tidy on a compact structure. Check bracket fit against your frame before cutting.
Why we like it
- Complete kit in one box
- Sized for small roofs
- Neat look
Keep in mind
- Small capacity in heavy rain
- Brackets may need adapting
Fiskars DiverterPro rain barrel diverter kit
$The Fiskars DiverterPro fits into a standard downspout and sends water to your barrel through a hose. When the barrel fills, water continues down the downspout instead of overflowing at the base. That overflow control is the main reason to use a diverter instead of dropping the downspout straight into a barrel.
Why we like it
- Handles overflow automatically
- Fits common downspouts
- Widely available
Keep in mind
- Needs a standard downspout size
- Disconnect in winter
EarthMinded rain barrel diverter kit
$EarthMinded sells diverter and parts kits that turn any food-grade drum into a rain barrel. It's a good pick if you're repurposing a drum or already have a barrel. The kit approach means you drill and fit parts yourself.
Why we like it
- Works with DIY barrels
- Low cost
- Includes fittings
Keep in mind
- Some drilling needed
- Fit depends on your barrel
Good Ideas Rain Wizard rain barrel
$$The Rain Wizard is a widely sold molded barrel with a screened top and a spigot, in several colors and sizes. It sits neatly beside a small greenhouse and works with a diverter kit. Set it on a stable, level stand so you can fit a watering can under the spigot.
Why we like it
- Screened top keeps out debris
- Several sizes
- Ready to use
Keep in mind
- Needs a stand for gravity feed
- Must be drained for winter
FCMP Outdoor rain catcher barrel
$$FCMP Outdoor's rain catcher barrels have a screened inlet, a spigot and overflow fittings, and several models are designed to link together. Linking barrels lets you capture more from a bigger roof. Check the listing for included fittings and a stand.
Why we like it
- Designed for linking
- Screened inlet
- Overflow fittings
Keep in mind
- Bulky to ship
- Stand may be extra
Collapsible rain barrel
$Collapsible fabric barrels fold flat when you're not using them, which makes it easy to put them away before a freeze. They're less sturdy than rigid barrels, but they suit renters and small greenhouses. Set them on a firm, level base, because they rely on it for support.
Why we like it
- Folds flat for winter
- Light and cheap
- Easy to move
Keep in mind
- Less durable
- Needs a firm base
Rain barrel linking kit
$A linking kit connects two or more barrels at the base so they fill and drain together. It's the simplest way to scale up once one barrel isn't enough for your roof. Place the barrels at the same height.
Why we like it
- Doubles or triples capacity
- Low cost
- Works with many barrels
Keep in mind
- Barrels must sit level
- More fittings to winterize
How to set it up
- Choose the gutter side. On a freestanding house, gutter the side facing where you'll put the barrel, or both long sides if you want more water.
- Fit gutters with a slight fall toward the outlet so water doesn't pool and freeze.
- Add a downspout from the outlet to the barrel location.
- Fit a diverter in the downspout, or run the downspout into the barrel's screened inlet with an overflow hose leading well away from the base.
- Raise the barrel on a firm, level stand so a watering can fits under the spigot.
- Carry overflow away from the greenhouse, ideally to a gravel soakaway or garden bed.
- Screen every opening to keep mosquitoes and debris out.
Winter: drain before the hard freeze
Water expands when it freezes. A full barrel, a diverter or a length of hose can split in one cold night. Before freezing weather:
- Disconnect the diverter and let water run down the downspout.
- Drain the barrel and store it upside down or inside, or leave the spigot open.
- Store hoses and fittings out of the weather.
- Check gutters for leaves so meltwater can drain.
Our winterizing greenhouse water guide has a full checklist. If you're thinking about keeping water barrels inside the greenhouse as heat storage, that's a different job. See water barrel thermal mass vs a backup heater.
Mistakes to avoid
- Dropping the downspout straight into a barrel with no overflow. The overflow pours out right at the base.
- Leaving barrels full over winter. Freezing splits plastic and fittings.
- Skipping the stand. A barrel on the ground can't fill a watering can.
- Drilling glazing to fit brackets. Use clamps or frame fixings, and check your warranty.
- Forgetting mosquito screens. Standing water breeds them fast in warm weather.
Off-season buying tips
Rain barrels and diverters are often discounted in fall as retailers clear garden stock, and again in late winter before spring. Fall is a good time to buy and install gutters too, since you'll see how your greenhouse sheds water in autumn rain. eBay is useful for linking kits, spare diverters and hard-to-find greenhouse gutter parts for discontinued models.
Frequently asked questions
Can you put gutters on a greenhouse?
Yes. Some greenhouse kits include gutters or sell them as accessories. For others, vinyl or mini gutter kits can be fitted with brackets or clamps. Check your warranty before drilling the frame, and never drill glazing.
How much rainwater can a greenhouse roof collect?
Multiply the roof footprint in square feet by the rainfall in inches, then by 0.623 to get gallons. An 8x12 greenhouse guttered on both sides collects roughly 60 gallons from one inch of rain.
Is rainwater good for greenhouse plants?
Many growers prefer rainwater because it's usually soft and low in dissolved minerals. Keep barrels clean and screened, and test pH and EC if you're growing sensitive crops.
Do I need a rain barrel diverter?
A diverter isn't required, but it's the easiest way to handle overflow. It fills the barrel and then sends extra water down the downspout instead of spilling it at the greenhouse base.
What do I do with rain barrels in winter?
Before hard freezes, disconnect diverters, drain barrels, and store them upside down or indoors. Leave spigots open if the barrel stays outside. Ice can split barrels and fittings.
Is it legal to collect rainwater?
In most places, yes, but a few states and localities regulate rainwater collection, and some HOAs restrict barrels. Check local rules before installing a large system.