Greenhouse Watering & Irrigation Guide: Manual vs Automatic Systems
Greenhouse watering systems range from a basic watering can to solar-powered drip irrigation costing £45 to £315. Hand watering suits greenhouses under 6x4ft, while drip irrigation reduces water use by 60% and keeps plants alive for two weeks on holiday. A 200-litre water butt connected to your greenhouse gutter collects over 20,000 litres of free rainwater per year.
Key takeaways
- Water greenhouse plants daily in summer, weekly in winter, always before 10am
- Drip irrigation is the best value method, cutting water use by 60% from £45
- A 200-litre water butt collects over 20,000 litres of free rainwater per year
- Inconsistent watering causes blossom end rot in tomatoes and fruit splitting
- Capillary matting on staging keeps plants watered for 2+ weeks on holiday
- Rainwater is better for plants than mains water: no chlorine, naturally soft, ambient temperature
Installer's Note
I have fitted over 500 greenhouses in 16 years, and the single biggest mistake new owners make is not planning their water supply before the greenhouse goes up. Running a hose 30 metres from the kitchen tap gets old by week two. I always tell customers: budget £50-£80 for a water butt kit and a drip irrigation kit before buying anything else. You will use them every single day from April to September.
How often should you water a greenhouse?
Watering frequency changes with the seasons. In summer, most greenhouse crops need water every day. In winter, once a week is enough for most plants. The single most important rule: water in the morning, before 10am. Evening watering leaves foliage wet overnight, which causes botrytis and powdery mildew.
Use the finger test before reaching for the watering can. Push your finger 2.5cm into the compost. If it feels dry, water. If it feels damp, leave it another day. Overwatering kills more greenhouse plants than underwatering, especially in winter when cold wet compost suffocates roots.
| Season | Frequency | Best time | Key notes |
|---|---|---|---|
| Summer (Jun-Aug) | Daily, twice daily in heatwaves | Before 10am | Tomatoes need 1-4 litres per plant per day |
| Spring (Mar-May) | Every 2-3 days | Morning | Seedlings need small, frequent amounts |
| Autumn (Sep-Nov) | Every 2-3 days, reducing to weekly | Morning | Reduce as temperatures drop |
| Winter (Dec-Feb) | Weekly or less | Late morning | Cold wet compost causes root rot |
Grow bags dry out far faster than pots. Check them two to three times daily in July and August. If you are growing tomatoes in a greenhouse, inconsistent watering is the number one cause of blossom end rot.
Six greenhouse watering methods compared
Every greenhouse watering system falls into one of six categories. The right choice depends on your greenhouse size, budget, and how often you can visit. Here is what each method costs and how it performs based on our experience fitting and advising on hundreds of greenhouses.
Hand watering with a can or hose
A watering can is the cheapest option at £10-£35 and gives you complete control. Fill your can from a water butt inside the greenhouse so the water is at ambient temperature. Cold mains water shocks plant roots and slows growth. Use a fine rose attachment and water at the base of each plant, never over the foliage. Hand watering suits greenhouses under 6x4ft with fewer than 20 pots. Anything larger becomes a daily chore that takes 15-20 minutes per session.
Drip irrigation
Drip irrigation delivers water directly to the root zone through tubes with small emitters. It reduces water use by up to 60% compared to hand watering because nothing is lost to evaporation or runoff. The Palram Canopia Drip Irrigation Kit costs £45 and includes 10 metres of drip line with 16 droppers, a 19mm adapter, and four T-connectors. It connects to any standard outdoor tap.
Shop the Palram Drip Irrigation Kit →
Run the main line along your staging or grow bag row. Position one dripper at the base of each plant. A single kit covers an 8x6ft greenhouse with 16 plants. For larger greenhouses, connect two kits with the included T-connectors.
Capillary matting
Capillary matting is an absorbent fabric that sits on your staging shelf. You keep one end in a water reservoir and the mat wicks moisture upwards into the pots sitting on top. Each square metre of matting holds up to 3 litres of water. Plants draw exactly what they need through the drainage holes in their pots.
This is the best holiday watering solution I have found. A 10-litre reservoir and capillary matting on a single shelf keeps 12 pots watered for two weeks without any electricity or timers. Cut the matting to fit your greenhouse staging, leaving a 2cm overhang into the reservoir. Capillary matting costs £4-£8 per square metre from garden centres.
Matt's Tip: Capillary matting only works with plastic pots
Terracotta pots do not draw water through capillary matting. The unglazed clay absorbs moisture sideways instead of letting it reach the compost. Stick to plastic pots on matting shelves. Also, never put gravel or crocks in the bottom of pots when using capillary matting. The air gap blocks the capillary action completely.
Automatic timer systems
An electronic timer connects between your tap and drip line, triggering watering on a set schedule. Basic timers cost £15-£25 and run once or twice daily. More advanced models like the Hozelock 25-Pot Automatic Kit (£79-£100) include everything: timer, tubing, and drippers for up to 25 pots.
If you are using a water butt instead of mains pressure, buy a low-pressure timer specifically designed for gravity-fed systems. Standard timers need 1-2 bar of mains pressure to operate. Raise your water butt at least one metre above the drippers for reliable gravity flow.
Solar-powered irrigation
Solar irrigation systems pump water from a butt or tank using a small solar panel. The Irrigatia SOL-C12L (£69) powers 12 drip outlets and adjusts watering frequency based on sunlight levels. On sunny days, it waters more often. On overcast days, less. No mains electricity and no mains water needed.
This is the best option for allotment greenhouses or sites without a tap. The C12L draws from any container and the solar panel charges an internal battery that keeps working for two cloudy days. A 200-litre water butt lasts one to two weeks in midsummer with 12 plants connected.
Overhead misting
Fine misting nozzles mounted 1-1.5 metres above the plants spray a fog of water droplets. Misting suits propagation benches and tropical plants that need high humidity. It is not suitable for tomatoes, peppers, or cucumbers because wet foliage causes fungal disease. Misting kits cost £30-£100 and connect to mains water. Use misting only in propagation areas, and combine it with good greenhouse ventilation to prevent humidity building too high.
Watering method comparison table
| Method | Cost | Best for | Holiday capable | Water saving |
|---|---|---|---|---|
| Hand watering | £10-£35 | Small greenhouses under 6x4ft | No | None |
| Drip irrigation | £16-£120 | Any size, tomatoes and grow bags | With timer | Up to 60% |
| Capillary matting | £4-£8/sqm | Staging shelves, holiday watering | Yes, 2+ weeks | High |
| Automatic timer | £15-£100 | Scheduled daily watering | Yes, 3+ weeks | Moderate |
| Solar-powered | £69-£350 | No mains water or electricity | Yes, 1-2 weeks | High |
| Overhead misting | £30-£100 | Propagation and tropical plants | With timer | Low |
|
Matt's Pick for greenhouse wateringBest For: Any greenhouse up to 8x6ft with tomatoes, peppers, or cucumbers in grow bags Why I Recommend It: I have fitted this kit in dozens of customer greenhouses. It takes 20 minutes to set up, connects to a standard tap, and the 16 droppers cover a full 8x6 growing space. Customers who switch from hand watering tell me their tomato yields improve because the plants get consistent moisture at root level. Price: £45 |
How to connect a water butt to your greenhouse
Every greenhouse with guttering can collect rainwater. A standard 8x6ft greenhouse collects over 20,000 litres per year from rainfall alone. Rainwater is better for plants than mains water because it contains no chlorine, no limescale, and sits at ambient temperature instead of shocking roots with cold tap water.
Shop the Vitavia Water Butt Connecting Kit →
The Vitavia Water Butt Connecting Kit (£24) fits all Vitavia greenhouse guttering and connects a standard 35mm downpipe to your water butt. Most greenhouses have guttering on both sides. Use a Y-connector to feed both downpipes into one butt, or fit two separate butts for maximum storage.
Choose a 200-litre butt as a minimum. A 100-litre slimline butt empties in a week during July. Place the butt on a raised stand so you can fit a watering can underneath the tap. If you plan to connect a drip irrigation system, raise the butt at least one metre above the drippers for reliable gravity-fed flow.
How to water your greenhouse on holiday
Going on holiday in July or August means your greenhouse plants face the hottest, driest fortnight of the year without you. Planning ahead saves the entire growing season. Set up your holiday watering system at least one week before departure and test it.
The cheapest approach is capillary matting with a water reservoir. Group your plants by water need and place them on matting-covered staging with one end in a tray of water. This keeps 12 pots alive for two weeks without power or timers.
For larger greenhouses, connect a drip irrigation kit to a water butt with a battery timer. A 200-litre butt set to water twice daily for 10 minutes covers an 8x6ft greenhouse for three weeks. Close vents to halfway position, apply shade paint or netting, and mulch the surface of every pot with bark chips to reduce evaporation. This is one of the essential greenhouse accessories that pays for itself the first time you go away.
Common greenhouse watering mistakes
After 16 years of advising greenhouse owners, I see the same watering mistakes every season. These are the problems I fix most often when customers ask why their plants are failing.
- Watering in the evening. Wet foliage overnight causes botrytis, powdery mildew, and damping off. Always water before 10am.
- Splashing water on leaves. Water at the base of each plant. Wet leaves in direct sun cause scorch marks. Wet leaves in shade cause fungal disease.
- Inconsistent watering. Alternating between drought and flood causes blossom end rot in tomatoes and fruit splitting in peppers.
- Using cold mains water. Fill watering cans 24 hours ahead or use a water butt so the water reaches ambient greenhouse temperature.
- Shallow frequent watering. Light daily sprinkles encourage surface roots that dry out faster. Water deeply and less often to push roots downwards.
If you notice blossom end rot on your tomatoes, the problem is almost always irregular watering rather than a calcium deficiency. Keep the compost evenly moist and the rot stops. This applies to peppers and companion planting combinations too.
Which watering system fits your greenhouse?
Match your system to your greenhouse size and growing style. There is no single best option for every situation.
- 6x4ft or smaller: Hand watering from a water butt inside the greenhouse. Budget £30-£50 total.
- 6x8ft to 8x6ft: Drip irrigation kit with a water butt. Budget £70-£100 total.
- 8x10ft and larger: Automatic timer with drip lines from a 200-litre butt. Budget £100-£200.
- Allotment with no tap: Solar-powered irrigation from a water butt. Budget £70-£150.
- Holiday cover only: Capillary matting on staging with a reservoir. Budget £15-£30.
Whatever system you choose, start with a water butt. It is the single best investment for any greenhouse. When you are setting up a new greenhouse, fit the water butt before you plant anything.
Frequently asked questions
How often should I water my greenhouse in summer?
Water greenhouse plants every morning before 10am in summer. Most crops need daily watering from June to August. Tomatoes in grow bags need 1-4 litres per plant per day depending on size and temperature. Check compost moisture by pushing your finger 2.5cm deep before watering.
What is the best automatic watering system for a greenhouse?
Drip irrigation with a timer is the best automatic system. It delivers water directly to plant roots, reduces waste by 60%, and runs unattended for weeks from a water butt. The Palram Canopia Drip Irrigation Kit covers an 8x6ft greenhouse with 16 plants for £45.
How do I water my greenhouse when on holiday?
Use capillary matting or a drip system with a timer. Capillary matting on staging keeps 12 pots watered for two weeks without power. A drip kit connected to a 200-litre water butt with a battery timer covers three weeks. Set up and test one week before departure.
Can I use a water butt with drip irrigation?
Yes, but raise the butt at least one metre above the drippers. Gravity-fed drip systems need height to create pressure. Use a low-pressure timer designed for water butts, not a standard mains-pressure timer. Solar-powered pumps like the Irrigatia range work at any butt height.
What size water butt do I need for a greenhouse?
A 200-litre water butt is the minimum for most greenhouses. A 100-litre slimline butt empties in one week during July. A standard 8x6ft greenhouse collects over 20,000 litres of rainfall per year, so a 200-litre butt refills quickly. Use two butts on opposite sides for larger greenhouses.
