Unheated Greenhouse Growing: How To Use An Unheated Greenhouse

In an unheated greenhouse, growing anything during the coldmonths of winter may seem impossible. Alas, it is not! Knowing how to use anunheated greenhouse and what plants are better suited is the key to success. Readon to learn more.

Using an Unheated Greenhouse in Winter

An unheated greenhouse in winter will not only allow you togrow hardy veggies, but you can start tender annuals, propagate perennials, andoverwinter cold sensitive plants. Of course, it helps to know how to use anunheated greenhouse (or “cold house,” as it may also be called) effectively andwhat plants will be most suited to this cooler environment.

During the day, a typical greenhouse will trap heat from thesun, which allows the plants inside to stay warm at night. That said, when winternights get really cold, frost damage in the greenhouse can occur without addedprotection.

What types of protection are there in lieu of greenhouseheaters? This can be as simple as the addition of one or two layers ofhorticultural fleece over your plants (Remember to remove coverings during the dayso they do not overheat.), and place some bubblewrap around your pots to help insulate plant roots and prevent clay potsfrom cracking. Horticultural bubble wrap can also be used by layering theinside of your greenhouse. The much needed sunlight will still come through butthe extra layer of protection will keep your plants safe at night.

Chances are good your unheated greenhouse is a simple coldframe or hoop type of structure. This structure is very simple to use inthe winter and fairly low cost. It should be situated so it is getting the mostnatural sunlight possible, out of the way of winds, and as close to a watersource as possible.

Keep an eye on the thermometer, especially when headingtowards spring. In many regions, temperatures can be in the 30’s one day and inthe 60’s the next (in a buttoned-up greenhouse it can be much higher). Plantsdon’t often recover from sudden overheat like that, so be sure to open thegreenhouse if temperatures threaten to soar.

What to Grow in Unheated Greenhouses

When you have a temperature-controlled greenhouse, the sky’sthe limit as to what can be grown through the winter months. However, if yourgreenhouse is a simple affair, lacking any heat, don’t despair. Using anunheated greenhouse can still provide you with plenty of options.

An unheated greenhouse can be used to grow greensduring winter, start warm season annuals, propagate landscape perennials,and shelter frost tender plants through the winter chill.

Besides greens like spinachand lettuce,you can grow cold tolerant veggies suchas cabbageand broccoliin your unheated greenhouse. Celery,peas,and the ever popular Brusselsprouts are also excellent cool weather veggie choices for unheatedgreenhouse growing.

Other winter greenhouse plants that thrive during wintermonths are root vegetables. Winter temperatures actually stimulatesugar production in some root veggies, so you end up with the sweetestcarrots, beets, and turnips imaginable. Don’t stop there with your wintergreenhouse gardening though.

Perennial herbs are another option – oregano,fennel,chivesand parsleydo well. Cool-hardy flowers, like calendula,chrysanthemum,and pansy,not only thrive in a cold house but will bloom through the winter. Many annualand perennials that may not be hardy in your climate outdoors will actuallyflourish in the greenhouse, even those that are seeded in fall will grow andproduce a bounty of blooms in late winter to early spring.

Plants for growing through winter in a greenhouse

Plants for winter are Winter Lettuce, Potatoes, Spinach, kale, cabbage, Bok choy, Chinese cabbage, Onions, Shallots, Peas, Broad beans, Garlic and Spinach. These plants can all be grown in an unheated greenhouse through winter, providing you follow a few guidelines

  • Get the timing right and plant them before the days get too short and before it gets too cold.
  • Planting now means you will be ahead of the game in springtime.
  • Bear in mind, unless you have some form of lighting in your greenhouse very little actually grows in the winter months of December and January. Things just tick over and then grow like mad when the days start to lengthen again, so don't panic, turn up the heat or kick the greenhouse, it is nature's way of giving you time for Christmas shopping.
  • More specific information further down this page)

Vegetables to grow in a greenhouse in winter

There are plenty of hardy vegetables that will grow well indoors throughout winter – here are our recommendations of the best ones:


The perfect winter ingredient, you can grow potatoes in either grow sacks or a large bucket/flower pot. We recommend filling your container with two parts garden soil to one part compost for best results. Potatoes started early in the winter season will be ready to enjoy by March, or you can start them later and then move them outside when the weather warms up. Potatoes can be susceptible to frost, so be sure to keep your greenhouse warm if the temperature drops significantly.

Winter lettuce

For the salad lovers, there are a few different types of lettuce that prefer the cooler environment. Little gem, rocket and lamb’s lettuce are all good – they tend to grow fairly quickly, so just harvest when you’ve got some big leaves you can use.

Pak choi

This oriental vegetable is a great addition to a stir-fry or noodle dish. Packed full of healthy vitamins and fast to grow, it can be sown as late as October ready for winter harvesting. Leaves take roughly 30 days, whereas the full plant will take closer to 70 days.

Spinach and kale

These leafy greens can readily brave the cold, which makes them perfect for growing during the winter. Growth times can vary, but you’re sure to have crops in abundance. Merlo Nero and Riccio d’Asti are good varieties of spinach to sow in an unheated greenhouse, and kale can survive in temperatures as low as -6C.

Cabbage and broccoli

If you manage to keep your greenhouse at the optimum temperature, both cabbage and broccoli can grow throughout the whole of winter. Start them early (mid-winter time) ready for planting outdoors in spring.

Brussel sprouts

Love or hate them, brussels are perfect for winter greenhouses. They take around three months to grow, so harvest them in March when they’re roughly 1-2 inches in diameter. If you’re going to be using them for cooking, be sure to harvest sprouts that are of a similar size – this will give them a more uniform cooking time.

The Very Best Vegetables To Grow In An Unheated Greenhouse

Eating fresh produce all winter is a gardener’s dream. There is a sense of pride and satisfaction from eating vegetables you grew in your own garden. Some may think growing crops during the winter is hard or impossible, but as you will see, winter gardening is easy and fun when you know what to plant — and when.

Cool greenhouses, cold frames or quick hoops are the easiest to handle and take care of. In most locations no heat is needed, as the structures absorb the sun and produce is protected from outside weather. Cool greenhouses or cold frames are greenhouses that stay below 50 degrees Fahrenheit consistently at night. You can also use quick hoops, a structure made with arches and built very much like a cold frame. They can have high or low arches. You can even place quick hoops inside a cold frame. This would give your plants extra protection and double the amount of plants you can grow.

With any one of these structures, there is a rather large list of vegetables you are able to grow easily. Let’s begin the list with beets, broccoli, garlic and kale. There are also Brussels sprouts, carrots, radishes, celery and turnips. Leafy greens like the cooler temperatures, too. Let’s bring in the cauliflower, spinach, cabbage, lettuce and herbs. When wondering about a vegetable, read up on its characteristics if you are interested in adding it to your garden.

The advantages of growing winter vegetables in a greenhouse or a cold frame are as plentiful as the types of vegetables they protect. A dedicated gardener is able to enjoy a beloved hobby, as well as having fresh produce during the dreary, long winter days. Very little weeding is necessary in the cold months.

When you are deciding on whether or not to grow through the winter, you need to know both the advantages and disadvantages. The cost of building a greenhouse structure can be substantial, even if you decide to build it from scratch instead of buying a store model. If you choose to heat the structure, or if you have more than one, it may raise your heating bill noticeably. But if you keep your greenhouse warmer, you will have more choices of what to grow. One way to get around this issue is to attach your greenhouse structure to your house, and share heat.

For some areas, crops such as kale, carrots or spinach can grow outside with little protection. Parsnips grow well mostly anywhere unprotected. Most of these crops enjoy full sun or partly sunny areas. The vegetables mentioned all have a reputation for being tough and resilient. Let’s talk about a few common ones. For example, parsnips are usually grown as an annual crop but are a hardy plant having a strong resistance to cold. They are at their best when harvested right after a frost. Carrots love the sun, and gamely fight off most garden pests and diseases. Root vegetables like carrots, beets and garlic can resist the frost. They all like a partly sunny to sun-filled area. They grow quickly and can survive frosts and freezing temperatures. Garlic is known for being a natural garden insect repellent and tolerates frost well. Spinach is tough and cold resistant. It is also a sun-loving plant just like the other vegetables mentioned here.

For a winter garden, you still need to treat soil like usual. You must build the structure and prepare the area for growing. You need to decide where the best place is to build the structure. You also need to plan what type of greenhouse suits your home and yard. It may take a couple growing seasons to understand what vegetables and structures work the best in your climate area.

Remember that you can grow new crops once you harvest the old ones. Keep an eye on the temperature inside the greenhouse, though. Over-heating is a common threat to greenhouse garden vegetables and needs to be taken seriously. It is just as serious as a severe frost. Plants will recover from frost, but not from being heated to the point of wilting. If you notice the temperature has risen over 75 degrees Fahrenheit inside the structure, open your greenhouse windows or cold frame a few inches for a while. It helps to keep a thermometer inside to easily read temperatures.

What a success it is to eat what you grew in your very own backyard greenhouse, in the middle of winter. Don’t let the threat of cold or snow stop you, for now you know the secret. Gardening isn’t just for spring and summer it’s a year-long activity. It will bring a piece of summer into your winter kitchen.

What are your winter greenhouse and gardening tips? Share them in the section below:


Throughout the winter months it was a daily experiment to keep it warm but now that the temperatures are starting to climb a bit outside, I have to remember each day to open the doors and window so the heat stays under control. I took out the bubble wrap insulation early in the month and have found that many days the temperature is climbing to over 100° inside.

I have planted a couple of potatoes in pots and have one that is looking really promising. I have covered it twice already with straw and additional potting soil. I’m hopeful that this one will continue to grow!

What are you growing in your greenhouse or gardens this month? I’d love to hear!

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