Organic Food Gardening

Mini greenhouses are smaller than full-size greenhouses, but big in usefulness! The term mini greenhouse can refer to several styles of greenhouse:

• A set of shelves for plants, with a plastic cover fitted over the top to protect them
• A very small conventional-shaped greenhouse, with a plastic sheet cover or rigid plastic glazing
• A lean to or closet-like greenhouse where access is “reach-in” but there’s much more space than the shelf-style units
• A cold-frame like structure
• Covered planter trays for starting plants from seed or cuttings

We’ll take a closer look at all these kinds of mini greenhouses in this article.

Shelf-Style Mini Greenhouses

This is a four-shelf 4 Tier Green House with a plastic cover which zips up on both sides to open the front completely. Plenty of ventilation like this is important with a small covered area as it can heat up very quickly when the sun gets on it.

Other mini greenhouses of this style come with 2 or 3 shelves instead of 4 – the 2 shelf versions are small enough to stand on a bench or table. The size you need depends on how many plants you plan to grow in them, whether seedlings, pot plants, tropicals, cuttings or overwintering herbs.

While these units are intended to be used outdoors on your deck or patio, they also work indoors to keep the atmosphere around your plants nice and moist.

I find a mini greenhouse like this most useful for hardening off the seedlings I start in my basement. Placed on the deck, right by the back door, mine is very convenient for opening and closing the cover, moving plants around to make sure they get even light, watering, and generally keeping a close eye on them. It allows me to expose the young plants gradually to the outside world, while taking up very little floor space, and in the summer I can take the cover off completely and use it for potted herbs and flowering plants.

Small Greenhouses

This tiny Walk-In Greenhouse is based on the same principle as the shelf units described above – a frame with a plastic cover which zips open – but it’s big enough to walk into and to have plants growing on both sides, either in the ground or in pots on benches or racks. Many other similar models are available.

Advantages include cheapness, and being portable – so you can use it on a deck or patio, or over a different garden bed at different times. This certainly beats moving all the soil out of a fixed greenhouse bed and replacing it, as some books advise you to do! It’s important to fix the greenhouse down well – as you can see, the model in the picture uses guy-lines and stakes, though on a patio or deck, weights would do the same job. You can also pack the whole thing away over the winter if needed, so no worries about it being damaged or blown away by winter storms.

One of my neighbors uses a small greenhouse like this for his tomatoes. Every year he plops the greenhouse over a different spot in the garden in the early spring and allows the soil to warm, plants his tomatoes a month earlier than he could if they were completely unprotected, gradually leaves the door open for longer as the weather warms, spends the summer picking great tomatoes while the cover keeps the rain and the blight off the plants, picks for a long time into the fall, then puts the greenhouse away for the winter until he chooses a new spot the next year. This is a great way to rotate your tomato crop to keep down diseases and pests.

Lean-To or Closet-Style Mini Greenhouse

This example is the Mini Greenhouse Model 2 with base from Juliana. Mini-greenhouses like this are often placed against a wall or fence, with access from one long side. Like the shelf-style greenhouses they can have shelves in, but they are several feet deep and so have much more growing space inside.

They can be placed over plants growing in the ground to provide an excellent warm micro-climate for something like a dwarf peach tree trained against a wall, but they also work very well for tall pot plants like standard fuchsias or other tender but large plants. An important feature you can see in the picture is a vent at the very top, where the heated air collects. You can make this an automatic vent which will help to keep the temperature under control even if you can’t open the main door.

My mother has had a greenhouse like this for about 20 years on her backyard patio and it’s always full, summer and winter, even though she has a large sunroom as well!

Cold-Frame Type Mini-Greenhouse

The Juwel Cold Frame 1000 is a cold frame style mini greenhouse. In many ways these are more useful over winter than the shelf style. Being closer to the ground, they often stay warmer, and are much less prone to being blown over by windstorms. It’s also easier to install an automatic opener to save having to run out and open the cover every time the sun comes out, though that does depend on the model you choose.

Bear in mind that once you have a cold frame, you’ll find a million more uses for it that you would never have thought of, so although a small one is cheaper it may be better in the long run to buy as large a model as you can fit into your space and your budget.

Covered Plant Trays as Mini-Greenhouses

These are a simple addition to the regular seedling trays – a clear cover which fits neatly on the tray and covers the plants. The covers come in two heights: about 2″, which is great for starting seeds where you will be removing the cover as soon as the plants pop up anyway; and about 7″, perfect for propagating cuttings where the rooting (we hope) plants have some height right from the start but you need to keep them in a moist atmosphere.

Either of these clear tops can be bought alone, or you can get them as part of a set with the seedling tray, cover, and peat pellets or cell packs to hold the plants. The best sets also include a heating mat which makes a huge difference when starting heat lovers like peppers, eggplant and basil.

Of course, you can also buy heat mats separately to work with the seed starting trays you already have. such as the Hydrofarm Seedling Heat Mat, which will work with standard trays in the 10″x20″ – 12″x24″ size range.