Greenhouse Gardening Tips

Watering tips for Greenhouses and Polytunnels

In our wet climate we don’t realise how much water plants use until we get a glasshouse or tunnel, and have to provide all of it ourselves.  What are the options?

Watering-cans are accurate and economical with water but very laborious to use for more than a few plants.  Hosepipes deliver more water but can splash mud and disease spores all over your plants.  Controlling the jet of water with the tip of your finger or thumb is an acquired skill.

Polytunnels often have overhead spray-lines.  They are effective, but spray everything below them whether it needs water or not, and if not hung perfectly level the lowest parts drip for ages after the flow is turned off.

Seep-hose, laid around and between your plants and dripping water from its many holes, is efficient and effective but doesn’t work well with pots.  Keep a watering-can for pots and trays and any additional spot-watering needed.  If water charges are a problem, bury the seep-hose under the soil surface so less water is lost by evaporation. For convenience when you are away, add a battery-powered watering timer to water the plants every few days.  It soon earns its cost in saved water and labour.

Water plants in the morning if you can.  This gives more time forFadrip tube at work wet leaves to dry off before evening, reducing the danger of Botrytis mould and other fungus problems that thrive in damp conditions.  A good soaking is better than little-and-often.

Soil temperature is more important than air temperature for plant growth.  To avoid chilling pot-plants and seedlings with cold water, refill the watering-can when you finish watering: the water will be warmed up to ambient temperature by the time you need it.

Written for Polydome by Peter Whyte B Agr Sc (Hort), Nat Dip Sc (Apic), Dip Tr & Ed, MI Hort

‘Cool’ ventilation tips from Peter Whyte

Bayliss XLNever mind how cold it is in your garden; the sun is getting higher every day and even short clear spells will allow it to build up a lot of heat in your glasshouse or polytunnel. You might think this is a good thing, but not always so. Lettuce seed won’t germinate if it’s too warm, and temperatures above about 35°C (95°F) will destroy the red pigment in ripening tomatoes so they never colour up properly. Overheated plants need more water to keep cool. As well as that, high temperatures put plants under stress and promote diseases such as grey mould and pests such as red spider mites. You can’t stand there 24/7, thermometer in hand, to open and close doors and vents with each change in temperature. Ordinary mortals adjust the ventilation once in the morning for the expected daytime temperatures and once in the evening for the night, and that’s near enough most of the time. The weather forecast can help you decide how much ventilation to give in the morning. A recording thermometer can show you how you did today, helping you to fine-tune your settings for tomorrow. End doors alone give enough ventilation for most polytunnels up to about 20 metres long. Side windows, roll-up vents and louvre vents are good but not cheap. Glasshouse vents can be fitted with gas-filled struts that automatically push them further open when they get warmer, without needing electricity. The best ventilation comes from a through flow of air, so open both ends of a polytunnel or more than one window in a glasshouse. Open many vents a little bit instead of opening two vents wide to reduce draughts. Be cool!

Peter Whyte (Lanscape and Garden Consultant) B Agr Sc (Hort), Nat Dip Sc (Apic), Dip Tr & Ed, MI Hort

Ready, steady, SOW

GT-DP-H 02Traditionally, people sowed vegetable seeds in their gardens on Saint Patrick’s Day.  That was because they were off work and free to do it rather than weather and soil conditions being suitable.  But, right enough, the soil is often dry enough to dig and warm enough for seed germination about then.

If you have a glasshouse or polytunnel you don’t have to wait for all that.  You can sow  crop seeds earlier under cover and have plants to put out instead of seeds, gaining several weeks of extra growth.   Sow leafy crops like cabbages and lettuce in modules for planting out later, and also a few seeds in the border soil inside to mature early.  If you have lots of room, keep one courgette plant growing inside until the outdoor-planted ones start fruiting.  You can then chop it out and use the space for something else, but it will have been cropping for weeks by then.

Tap-rooted plants such as carrots can’t be transplanted and don’t take kindly to modules, but you can still sow some inside for early crops.  Freshly-dug baby carrots, washed instead of peeled, and eaten raw are fit for a king.

Seedlings are easiest to raise in a heated propagator.  If using it inside the house carry the seedlings  out to a glasshouse or tunnel in the propagator with the cover closed to protect them from cold winds as the temperature shock would be too much for them.

The sun is getting stronger, so be prepared to open vents or doors on sunny days.  But make sure to close them at night!  Throw a sheet of bubble-wrap or fleece over plants on frosty nights.

Spring is sprung

Spring is sprung,

The grass is riz,

I wonder where the greenhouse is!

If you haven’t been in your greenhouse for so long that you are asking the above question, that’s okay.  You own it, and if you want to take a break from all gardening over the winter, that’s your decision.  Maybe next winter you will have green herbs and vegetables and some nice flowers, but what will you do now?

It’s time to spring-clean if you didn’t do it in the autumn.  On a dry and not too windy day, wash the outside of your glasshouse with a sponge mop and warm water with some washing-up liquid.  Hot water might crack the glass, and cold water is too darned uncomfortable when it runs up your sleeve!  Work from the ridge down.  Plastic tunnels are best left alone, or if badly affected with green algae washed very gently indeed.   Tidy up around the greenhouse and renew any gravel or bark mulch.

The inside can be done in windy weather without suds blowing in your face, but use a horticultural disinfectant instead of washing-up liquid if pests or diseases have been a problem.  Take out all crop remains.   Take out all pots and either empty them or tidy the plants up for bringing back in later.   Repair the path if needed and dig over the borders, adding in organic matter if you have it (it decomposes faster in the heat of a greenhouse).  Wash out empty pots and seed trays with garden disinfectant.

Now you’re ready to sow early vegetables such as carrots, ‘Hispi’ cabbage, and salad crops in the greenhouse, and many more for planting outside later.  Annual flowers too.  Enjoy!


Peter Whyte

B Agr Sc (Hort), Nat Dip Sc (Apic), Dip Tr & Ed, MI Hort

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Come and visit our extensive Display Area in Birr, Co. Offaly and get expert advice.
We currently have 21 Glasshouses on display, the largest display of Greenhouses in Ireland.


Greenhouse Display Area

We now have 15 Glasshouses and 4 Polytunnels on display at Polydome’s HQ at Crinkill House in Birr.  With Birr Castle Demesne close by any green fingered people looking for a Greenhouse (Glasshouse or Polytunnel) will find the trip well worthwhile.  As well as seeing the largest display of Greenhouses and being able to talk to product specialists to sort you out with the best Greenhouse or Greenhouses Accessories for your situation, with good places to eat locally and the renowned Gardens and Science Centre at Birr Castle it will be a great horticultural day out.

Tullamore Show

The recent Tullamore Show was a great success for us despite the showers.  Great interest in our new zig zag rails which are a new low cost system for attaching polythene to the Polytunnels – around the same price as a Timber Rail but much more durable.  The funny thing was the rain meant everyone dived for cover during showers so our Polydome Tunnel was full to capacity with a captive audience.  The show is a great day out for the family.

New Doors on our Display Tunnel

We have installed double sliding doors on our 5.5m wide Display Tunnel.  They look great and overcome issues hinged doors can have on windy sites.  A strong magnet keeps the two doors together when closed.  More new products coming on stream shortly and as well as our 4 Polytunnels on display we now have 11 Glasshouses so far up as well.

Greenhouse Display Area Progress

Glad to say our Greenhouse Display area is progressing well.  We have 9 Glasshouses and 4 Polytunnels up so far with more to come in the coming weeks and months.  Our plan will be over time to develop the area to show not only the huge range of Greenhouses and Polytunnels we do but also giving examples of how they can be laid out, which is a question we are often asked by customers.  We will also over time kit out many of the Greenhouses and Polytunnels with all sorts of accessories to demonstrate their use, so our display area will not just be for visitors wanting to buy a Glasshouse but a destination for proud owners of Greenhouses wishing to enhance and utilize their investment to its full potential.  Our display area is open from 9am to 5.30pm Monday to Saturday (closed for a well deserved break between 1 and 2pm).  Why not phone and make an appointment to ensure a specialist for the product you are interested in is available and minimize your waiting time.

Display area progressing

After a busy spell of servicing orders with no time available to get our own Greenhouses up, we have finally had a window of opportunity to go at our own display area.  We have built the frames of four more Greenhouses bringing the total to 8 so far on display as well as 4 Polytunnels.  In the coming weeks we will complete these models and add a few more that we have in stock.  It is great to see some growth now with the newly laid lawns giving a lovely green carpet – so it is out with the mower tonight.

Display Greenhouses multiplying

Progress being made on display area