Growing Cucumbers In The Greenhouse

On a hot summers day nothing tastes more refreshing than a sweet, juicy cucumber.

However despite being an integral part of many salads, it seems that very few people actually try growing cucumbers when compared to other popular salad crops like tomatoes, lettuces or radishes.

Growing cucumbers can arguably be a little more troublesome than these competing crops.

However you’re going to discover that growing cucumbers is actually within anyone’s grasp.

Furthermore it can be not only simple but also highly rewarding for anyone that owns a greenhouse and has a little space to spare.

Growing Cucumbers: Understanding The Two Main Types Of Cucumber

Generally speaking the cucumbers that are grown at home can be seperated into two distinct groups. The first of these groups are the so-called “ridge cucumbers” while the second are the “greenhouse cucumbers”.

The phrase ridge cucumbers refers to cucumber varieties that one grows outside. The “ridge” part of the name comes from the way they were classically grown and they are characterised by a smaller overall size than greenhouse cucumbers as well as protection in the form of small spines or ridges along their length.

growing cucumbers
Growing greenhouse cucumbers (left) versus ridge cucumbers (right).

On the whole, unless you’re growing cucumbers in a very warm part of the world, even ridge cucumbers can struggle outside in the average temperate summer. The fact is that cucumbers like a warm and humid environment and without the necessary heat your plants may struggle.

In contrast greenhouse cucumbers resemble the fruits you buy at your local farmers market or supermarket. They’re long, smooth and delicious-looking without the ridges or spines. In my experience they tend to be sweeter and juicier too so there really is no competition at all.

For me, greenhouse cucumbers look better, taste better and, thanks to the greenhouse environment and the artificial warmth and humidity this can create, I also believe they are easier to grow so that’s where we’re going to be focusing our time today.

Selecting The Right Cucumber Variety

There are a variety of different greenhouse cucumber varieties on the market but be aware that the better ones aren’t cheap. That said, when growing cucumbers you’ll find that just one or two well-grown plants can be enough to provide a constant supply of cucumbers for six months  or more so it’s a small investment for such a heavily-cropping plant.

Examples of popular greenhouse cucumbers include Telegraph and Conqueror though there is one additional factor that can help you to make an informed decision about the best variety for you.

The average cucumber plant will produce both male and female flowers. Female flowers will produce cucumbers whether they are fertilized or not, but those that have been fertilized are often found to be more bitter than cucumbers produced from unfertilized flowers.

Because of this, many people growing cucumber over the years have found it necessary to keep a constant eye on their plants, removing male flowers as they open to ensure the sweetest crop possible but this can involve plenty of work in the summer months.

In contrast there are now a number of “all female” varieties that don’t produce male flowers at all – and in terms of producing the sweetest cucumbers possible and cutting down on your workload it can be a wise idea to seek out these particular varieties. When combined with the ease of growth some of the best varieties currently on the market include Topsy and Birgit though the variety I have had so much success with is Paska.

Growing Cucumbers: Germination

Planning Ahead for Fall

Many horror stories surround the germination of cucumber seeds and the problems that gardeners and small holders have had in the past. However if you provide the right environment – namely a warm, moist and rich compost – most viable seeds will germinate very quickly indeed and within a few short weeks you’ll find that you’re the proud owner of some baby cucumber plants.

To get the longest cropping season possible one should aim to plant cucumber seeds early in the year. In most temperate areas March and April seems like a good time. Too much earlier and your greenhouse will still be too cold. Too much later and you’ll miss some of the growing season and cut down the total fruits you receive.

The process I use is to take a small flower pot and fill it with rich peat-free multipurpose compost. Press the seeds into the surface so they are buried to a depth equal to the length of the seed. Then soak this in a tray of water for 12 hours so that the compost absorbs plenty of water and feels damp to the touch.

Next, place the pot into a clear plastic bag that will keep in the moisture and some of the warmth whilst still allowing you to see when your seeds germinate and place the pot into a warm environment.

A sunny windowsill can work, as can an airing cupboard if it’s checked regularly. Personally I like to use a small heat cable or heat mat – which can be bought very cheaply from garden centers or reptile shops – which raises the soil temperature to 20-25’C and provides the perfect encouragement your seeds need to germinate.

Within a week or two under these conditions you should find seedlings appearing. These are normally healthy and vigorous and will grow strongly on a brightly-lit windowsill.

Growing Cucumbers In The Greenhouse

Once the seedlings have germinated you can turn off any supplemental heating and by the time they’re 3-6″ in height they should be strong enough to plant into their final position in your greenhouse.

Cucumbers like plenty of organic matter and water so aim to add some good quality compost or natural fertilizer to the area you’re going to be growing your cucumbers. Whether you opt to plant them straight into the soil of your greenhouse or put them in pots is up to you.

It’s worth bearing in mind that cucumbers can struggle if their roots are waterlogged so careful watering is essential if your plants are to thrive. For this reason growing cucumbers in containers inside your greenhouse may prove the more effective solution because it is easier to monitor and control soil moisture under these circumstances. Cucumber plants can attain impressive proportions so a pot of 12″ at the bare minimum should be used though the bigger the better.

Remember that cucumbers appreciate a warm environment – something that in April or May can still be something of a luxury. As a result don’t be too concerned if growth appears slow at first; the plants will be getting established and growing their root network and as the weather warms up so you’ll see growth rates increasing too.

growing cucumber plant showing baby cucumbers

Cucumbers also favor direct sunlight to help them generate sugars and grow rapidly so try to give them the sunniest spot you can. This year I grew three plants in slightly different light levels and the plant in the sunniest spot has grown twice as big – and produced many times as much fruit – than the plant in a slightly more shaded location.

Greenhouse cucumbers are climbers so start them off with a garden cane and gently coax the growing tip up the support, supporting it with garden twine as necessary to prevent the growing stem from falling over sideways and harming the plant.

When your cucumber plants reach the top of the support – which can happen pretty quickly in warm weather – I then create a “mesh” of garden twine across the roof of my greenhouse so that the growing cucumber plants can ramble wherever they like yet are still fully supported from damage.

Harvesting Your Cucumbers

Unlike a crop like sweetcorn or shallots where the whole crop becomes ready at the same time, growing cucumbers is more like growing tomatoes in that there is an extended season. Cucumber plants may begin to produce fruit when they’re only a few feet in height and as they grow they produce more and more fruit.

You’ll know that things are going well when you see the simple yet attractive yellow flowers beginning to open. As the flower dies, you should find a tiny cucumber behind it that grows and swells over a period of weeks.

growing cucumbers in your grrenhouse

Cucumbers should be picked early and often, especially early on in the season. Doing so not only ensures you an early first crop and beautifully sweet cucumbers but also encourages the plant to keep producing more. If growing cucumbers are left on the plant until they start to mature and turn yellow you’ll find that your plants reduce or even stop producing so regular harvests are essential.

Simply select the largest cucumber you have and carefully cut it off the plant with secateurs or a sharp knife. When you do so, the plant will redirect it’s energy to the next cucumber on the plant which, too, will start to grow at a faster pace.

As mentioned earlier on, with vigorous plants you’ll find that just one or two plants can provide a non-stop supply of cucumbers for you; I’ve been picking one a week for the last 4 months and the plants are still going strong so when you get your cucumber growing technique right it really can be a “gift that keeps on giving”.

Common Cucumber Growing Problems (And Their Solutions)

Growing cucumbers needn’t be hard but there are three common problems that cucumber growers experience time and again so it’s worth us covering these here as it’s likely you’ll suffer from them sooner or later.

Fortunately while they may look like the end of the world, all three potential problems are easy enough to resolve if you notice them early on and react appropriately to them.

Cucumbers Not Growing

The most common problem experienced when growing cucumbers is that the flowers open and the baby cucumbers start to grow, then when they’re just an inch or so in length they wither away and die. Your hopeful-looking green cucumber turns into a faded, brown, wrinkled object that eventually drops off.

If you’ve followed all the other guidance on warmth, sunshine and plenty of organic matter then the most likely problem here is either waterlogged roots or a lack of humidity in the air.

In these instances stop watering your cucumber for a few days but instead water the floor of your greenhouse. In this way the water will evaporate from the floor, increasing the humidity, while the cucumber’s roots will have a chance to dry out.

Pay close attention to the plants and you’ll normally find that the problem quickly subsides and while old cucumbers that have died won’t regrow, you should find that the new fruit quickly takes. Normally this problem only affects the very tiny baby cucumbers and once they reach a couple of inches in length you should be in safe territory again; all you need now is a little patience while they fatten up ready for your plate!

Stem Rot

Like tomatoes and other more “Mediterranean” crops, in cooler climates there is a risk of stem rot. This manifests itself at the very base of the stem, where the plant touches the soil, where the stem turns an unhealthy brown rather than the healthy green it once was.

In these instances try piling on plenty more compost around the stem base. This will bury the brown stem and encourage the healthier parts of the stem further up to start putting roots into the new substrate, strengthening the plant and prolonging it’s life. So long as the rest of your plant looks healthy it’s generally safe to assume that you fixed the problem.

Yellowing Leaves

Growing cucumbers are vigorous plants – growing fast and producing lots of the fruit in the right conditions – and as a result they can also use up a lot of nutrients. If nutrients are in short supply the plant can almost “starve” as it pushes all the available nutrients into producing fruit, causing it’s laves to yellow and die.

In cases where you see this occurring, try feeding weekly with a liquid tomato fertilizer which will return nutrients to the soil. While badly yellowed leaves are unlikely to recover, the new influx of nutrients should help to keep your plant healthy and vigorous and allow it to produce new leaves for photosynthesis.

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