Growing toms in an unheated plastic greenhouse?

Fire · February 2021

I have a friend who is a suer-keen newbie gardener. The first thing that she ever grew was tomatoes from bought plants last year. They were a great success and she is gagging to try vine toms from seed this year. She has a small south facing patio garden. She is thinking of getting a small, flappy plastic greenhouse for the toms. Can you describe any advantages in getting toms going earlier, if there are any? Does this type of greenhouse protect from frosts? She would not be using heated mats.

This article says March is fine for toms in a greenhouse.

T&M say "Sow your tomato seeds in March or April, approximately 6-8 weeks before the final frost of the winter, or earlier if you're growing your tomatoes in a greenhouse. " That would suggest you could sow toms now. (?)

Would you say to get them germinating in the house and then prick out and put them in the GH? What might be the time advantage of sowing toms in Feb? Would it really steal the march to plant them so early, compared to, say, waiting until April?

All thoughts welcome.

Image: https://us.v-cdn.net/6030279/uploads/editor/25/t3n3f03w163e.jpeg

steephill · February 2021

https://www.tomatogrowing.co.uk/ has some advice. Scroll to the bottom of the page for a section on when to plant out in an unheated greenhouse - basically end April/May. Small greenhouses have lots of problems, condensation, temperature control and just size if you are growing cordon varieties.

purplerallim · February 2021

Something like the picture would need some heavy duty restraints to keep in place @Fire ,maybe fixing to a wall.
As for use best not to start seeds till March give six to eight weeks inside growing on, and then out in May in final pots. It's easy to zip them up over night till the frosts finish, but you should be OK in London.😁 It will give a couple of extra weeks at the end in September too.

Skandi · February 2021

I grow all my toms in a greenhouse BUT if I had a nice south facing sheltered patio I wouldn't bother, I would go with sungold and a couple of other cherry types and just grow in pots on the patio.

I think she will get better plants with less hassle having them in the open. I do not plant my tomatoes in the greenhouse until ALL chance of frost has gone, a greenhouse give a maximum of 1-2C protection and I am not risking my precious babies.

The advantages would be being able to grow larger tomatoes, so beefsteak for example, they will rarely ripen outside. a second advantage is if we have a bad summer the greenhouse might mean the difference between tomatoes and no tomatoes, but I don't think one that size would do much and the plants will outgrow it very fast.

Ceres · February 2021

Don't be tempted to start growing tomato plants in February as the light isn't good enough and they will grow spindly and weak. Best to wait until later in March when the plants should get off to a good start and will be stronger and more robust and won't need staking from the moment their first leaves appear. I know how tempting it is to plant the things early......the odd glimpse of spring sunshine can make us all desperate to get the growing season underway but the plants won't thank you for it.

They will need to be started indoors and gradually hardened off before going into the greenhouse when the risk of frost has passed. Only a heated greenhouse will protect plants from frost.

The only advantage to growing tomatoes in a greenhouse is protection from wet and windy weather and a slightly earlier crop. The disadvantage of growing them under glass is the problem of excessive heat when the temperature hits 30 degrees outside and the glasshouse feels like a transparent sauna. I don't know how hot a plastic greenhouse would get but with a huge opening in the front, it should be easy to keep it well ventilated.

edhelka · February 2021

I used to have a small plastic greenhouse (used to because they don't last long). It absolutely doesn't protect against frost but it does protect against cold or damaging winds. I would say in mild areas, tomatoes can go to an unheated greenhouse/plastic greenhouse in early May, maybe in late April if the forecast is good, but not sooner. There are not good light levels inside to sow tomatoes in February and the night temperatures outside in April can be still very cold. Even if they aren't anywhere close to freezing, they can stunt the growth.

Fire · February 2021

Thanks. I have passed the comments on to my friend. That is basically as I imagined. I'm not sure the plastic greenhouse confers much of an advantage. She does have cats and dogs and foxes that tend to knock things over and eat the produce, on this small patio, so the GH might serve to protect stuff from animals. On the other hand, I have told her that cats and foxes used to jump on the roof of my small GH and knock it over. Such a GH stands a good chance of becoming just more plastic landfill.

Blue Onion · February 2021

I would recommend she purchase some sort of wire shelving similar to this or whatever size suits, with bricks or other weight on the bottom shelf. Start her tomatoes off indoors on a windowsill with a grow light (they are very inexpensive these days, and LED will last years of spring seed starting). Once it's time to harden off she can put them on the shelves outdoor wrapped in an old clear shower curtain or horticulture fleece for increasing amounts of time - bringing them in at night. I have mine in a clear plastic tote to take them easily back and forth into the house or outside. They live in the tote for several weeks until completely hardened off. Makes watering much easier too.

She can grow them up through the wire shelves if she wants, as sort of a frame, once they are ready to live outside. She can still wrap the plastic or fleece around at night or in bad weather.. but it's pretty easy to 'cook' a plant in those small plastic greenhouses even when unzipped on a cloudy day.. best to be careful.

Fire · February 2021

I just don't think there is much point to such a greenhouse. Is there any advantage to it?

thrxvs · February 2021

Must admit I am a bit surprised at some of these comments and I will stick my neck out a bit here... our tomato reigime is as follows (we grow mostly heritage but quite a few more common ones as well inside and out and obviously it depends on the type but you can start sowing as early as end of Jan although will need to look after these quite intensively). We in the east midlands, for context. The "tomato year" in the greenhouse is like night and day compared to the tomato year for tomatoes we grow outside.

Mid - end Feb : sow seeds in tray next to radiator or heated mats in very warm place inside the house. They need heat to germinate then can have less heat but then want light. After germinating when 1 - 2 cm high transplant into small pots and move into very bright and sunny dining room in front of french windows and near 2 radiators. Any room with lots of light and some heat will do. They are happy enough with the light there to grow reasonably well. (we sow seeds right up until end March depending on the type).

Mid April (believe it was 13th April last year, we had a cold day a couple of days before) plant in greenhouse, some direct into the soil in the greenhouse and some in large pots, harden off a bit first - if temps are ok then out in greenhouse for an hour or so then back in, next day 2 hours in greenhouse then back in etc etc. In my experience tom plants in the ground always do much better than those in pots. Key is to get the ground warm enough. We warm the soil first with old carpets and kept them there around the plants for a while, but after planting we didn't use fleece, other additional protection, or any heating in the greenhouse or anything else to warm the soil or environment so didn't even try to push things to see how early we could put them out, I am confident if we did push the boundaries a bit we could have planted them out a couple of weeks earlier maybe even end of March! (We never plant toms outside till mid May at the very earliest)

In my experience it is almost impossible to heat up and retain heat with a heater in a greenhouse to make any significant impact, they are by design a very poorly insulated structure that retains almost no heat (but that is a different conversation) so you need to protect the plants by more direct methods rather than focusing on the greenhouse itself. Fleece will help against frost if draped over plants, pop one or more plastic bottle or cloche over small plants for double insulation, and you can get varieties of toms that are designed to be more hardy. Sometimes you have to be inventive to make sure you protect the plants! Greenhouse heaters in my experience are generally little to no use. If can put a biggish pile of wood chippings or compost on the ground in the greenhouse and your plants on shelves above, the heat generated will rise and make a 2 -3 degree difference which is most welcomed during those cold nights. Basically the sooner you can get your toms out into the (appropriately warm) soil the better the results. Yes the risk is there is a frost but as I say get out there and be prepared, use fleece to cover the plants liberally and they will be fine. It is very unlikely that frost will kill or seriously stunt your toms as long as you are prepared, keep a very close eye on the forecast and react to it, and don't push the planting out time to be too early!

This might be useful reading and has some interesting experiences: https://northernhomestead.com/

Fire · February 2021

Thanks @thrxvs for your comments. I would wonder if your comments apply to a thin plastic, foldy greenhouse? Essentially one of those seems to make little appreciable difference to night temps before May. My friend's toms would def'ly be in pots. When would you get your first ripe toms?

Last year she bought small plants and did the oki koki (inside house/outside) from late March, protecting from frost with fleece/bubble wrap, and she seemed to get the first fruit the same time as everyone else.

Growing toms in an unheated plastic greenhouse?

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