Greenhouse Evaluation

As you may know, we have a plastic walk-in greenhouse that sits on the patio right next to the house, along with two smaller greenhouses that are essentially a plastic-wrapped stand of shelves.

Patio Greenhouses

Thankfully, they are temporary and are only there to keep the worst of the winter weather off the more tender or younger plants we have. Once the risk of hard frost is past (some time in late March?) then it will all come down and we will have our view out of the patio doors restored as currently it looks like this:

Winter Garden View

It’s not ideal and I am beginning to tire of it; I want to be able to see the birds again and the orchids could really do with more light. Nevertheless, the greenhouses do a very good job of stopping the cold air, bitter winds and damaging frosts from getting at the things inside. Greenhouses are new to me and I am still learning about how to use them. I’ve made the following observations so far with the ones we have:

  • In the larger greenhouse, there will be colder and warmer zones so plants should be placed accordingly if possible. The coldest areas are closer to the door and along the sides at ground level. Warmer places are on the raised shelving closest to the house. This can make the difference between life or death for tender plants such as the lemongrass. 

Expired Lemongrass

  • Plants barely need to be watered and should be kept on the dry side, which is a bonus as it means less work
  • The inside of the greenhouse will be constantly covered in water from heavy condensation, it will even drip from the roof as a kind of rain. If you’re not wearing head gear inside, do not hit the roof unless you want freezing cold water to run down your neck and back
  • Adding an insulating layer of bubble-wrap on the inside of the larger greenhouse is a must for when temperatures really nose-dive
  • Keep an eye out for critters such as whitefly, caterpillars and slugs that will eat your plants alive or suck them dry:

Munched Abutilon

  • As it is so moist in the greenhouse, it is the perfect environment for mould, moss and fungus. Plant die-back should be cut out and removed from the greenhouse to keep the mould down. Healthy plants won’t usually succumb to fungal infection so although the mould looks horrible, it’s not a big deal

Mossy Seed Trays

  • Temperatures inside the greenhouse can still drop below zero during extended periods of cold weather. The water on the inside cover and on the bubble-wrap can freeze, but you wont see frost on the plants themselves. I don’t know why this is, but it is a big bonus as frost on more tender plants can cause a lot of damage or kill
  • A “thick roof” on the smaller greenhouses (ours is a transparent plastic car mat placed on top) will be better at keeping the heat in
  • Ensure you’ve got sufficient weight and pinning to stop the greenhouses from getting airborne in times of windy weather

The points above will be useful “notes to myself” for when the times comes to have the greenhouse back up again next winter.

10 Comments


  1. I didn’t realise you had so many greenhouses. Impressive commitment! I can see why you can’t wait to move them. How did you manage to start off your lemongrass? I tried to start one in a jar of water but it didn’t work. Are you actually going to get lemongrass for cooking from it?

    Also, another question: did your Astrantia seeds ever germinate and if so, how did you manage it?

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  2. Hi Claire, the lemongrass came from the dry, wizened, exorbitantly-priced sticks you get at the supermarket. They’re not very fresh and the success rate will be low. If you go to an international food shop, they may have better, fresher ones that you’ll have better luck with.

    In a good year you can get lots of lemongrass stalks (for thai cooking) and leaves (for ginger tea) but you’ll need patience for one stick to develop into a substantial clump, but it will get there. The one in the picture above is probably dead now, but I have three stalks from it on the go already that will replace it.

    Once you see the bright green juicy fat stalks of real lemon grass you’ll never buy the pathetic excuse for it they have in the supermarkets ever again.

    The Astrantia is sown in a seed tray and is shoved somewhat unceremoniously underneath a rosemary shrub. I’ve left it out to scarify over the winter and will see if they germinate in the spring. I’ve also got seeds in a sealed tub that are outside scarifying too and will sow those in Spring to see how they go.

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  3. Hi Sunil. Your greenhouses set up is impressive. I do not have a greenhouse, we really don’t have a good location for it and I honestly would not dedicate the necessary time. Yours are impressive, though!

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    1. Hi Jason, the patio isn’t a great location for it either as it blocks the view, I’m looking forward to taking it all down but can’t do that until we’re well into Spring!

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  4. Hi, Sunil, I love how useful blogs are as “notes to self” for things that we’ll have long forgotten by the time the need to remember them rolls around again. I’ve tried putting a hoop with shade cloth over my raised veggie garden but it sits right outside the kitchen window, and I couldn’t stand looking at it all winter. You are a more dedicated soul than I — especially with all that freezing cold water running down your back and neck! Dave at The Anxious Gardner uses pitcher plants and maybe some other carnivorous plants to keep pests at bay in his greenhouse — maybe those would be of help?

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    1. Hi Stacy, thanks, it’s the little slugs and caterpillars that are a problem, but they’re honestly not too bad. I just need to keep a watchful eye out (and blue slug pellets around) t make sure it doesn’t get out of hand.

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  5. Sunil, Thanks for posting this. Since I’ve been thinking about a plastic greenhouse like hours as a way to overwinter some tender perennials in my Maine garden, this evaluation is very helpful.

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    1. Hi Jean, you could use temporary plastic greenhouses to protect your rosemary through the winter (you’d have to transfer them into pots first though). That will keep the frosts down, the wind off and heavy winter rains off too, which should go a long way to keeping rosemary happy.

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  6. Sunil
    Those temporary greenhouses are very handy and they can last a good few years. I have noticed that with pollybubble the condensation thing gets even worse, but what can you do. I suppose if we set one of those greenhouse fan heaters at about 46f it would help, seems extravagant though.

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    1. Hi Alistair, I’ve also found that the plastic goes brittle in the rain and sun and becomes useless after a few years. The bubble-wrap is essential in the larger greenhouse to help keep as much heat in as possible but you’re right, there’s condensation everywhere and I’ve needed to keep an eye on the mould and fungus. Although a greenhouse heater would keep my mind more at ease, I’m trying not to get too dependent on keeping things in the greenhouse as I don’t want to end up with a garden full of tropicals that need to be packed away and pampered every winter!

      Reply

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