The Secrets To Growing Cucumber Plants From Seed

Cucumbers are by far the most difficult vegetable to grow in our climate, but we will show the best way of growing cucumber plants from seed successfully.

Vegetable gardening is all about the challenge and getting a good crop of cucumbers really does show how good of a gardener you are. This might make you wonder why grow cucumbers in the vegetable garden at all? Well, the taste, texture and crunch of fresh cucumbers is like nothing you can ever buy in the supermarket.

It is possible to get a brilliant crop of cucumbers with some attention, by providing enough heat and preventing any sort of drafts.

In this article you’ll see how I go about growing cucumber plants from seed to get an incredible crop of fruit in an unheated greenhouse and good crops outside (even given our unpredictable summers).

The Best Cucumber Varieties To Grow

variety of mini cucumbers

Choosing the right variety is the first important step when growing cucumber plants from seed.

Over the years, I have found that varieties that produce mini cucumbers are most successful in the greenhouse. For outside crops, the old heritage varieties seem to be hardiest and more reliable in a bad season.

Here are some varieties to try out:

Mini Munch: as the name suggests, this is a variety that will give you small fruits (about 7cm or 3in), therefore it is ideal to grow in a greenhouse. This is a gynoecious variety, which means it produces mostly female flowers, which means more fruit. The cucumbers have a great flavour and a crunchy texture.

Socrates F1: this is another variety that produces small fruit and is perfectly suited for being grown in a greenhouse. Like the Mini Munch it’s an all female flower cucumber plant and produces large crops. They are also very tasty.

Marketmore: this is one of the popular outdoor varieties with a great flavour. It’s a reliable variety that will give you a high yield. The fruits grow to about 20cm (8in).

Carmen: this is a popular variety for the greenhouse. It has good disease resistance to many cucumber diseases. The fruits have a mild and delicious taste.

Burpless Tasty Green F1: this variety can be grown in the greenhouse or outside, depending on your preference. It has a fabulous taste and gives a high yield.

The varieties that will grow well outdoors are ridge cucumbers. They should not be grown in a greenhouse, as there is a risk of cross pollination, which will make the fruits taste bitter.

It doesn’t matter if you intend to grow your cucumbers indoors or outside, they will first need to be started in a greenhouse or on the windowsill as they need to be indoors until well after the last frost.

Now let’s get to it and looks at the secret of growing cucumber plants from seed.

Sowing Your Cucumber Seeds

cucumber seeds

Cucumber seeds are large and very easy to germinate. Sowing should begin in March for indoor crops or April for outdoor growing. The seeds should be quite quick to germinate, generally 7-10 days, but starting them in a heated propagator gives the plants the very best start possible.

A 10cm (4in) pot is the ideal place to begin the seeds, but a module tray is also acceptable if you intend to grow a larger number of plants. The seeds should be sown in a damp compost about 1cm (about 1/2inch) below the surface. Planting the seed on its side is thought to prevent the seed rotting and increases germination rates.

Make sure you don’t overwater the pots, as this will cause the cucumber seeds to rot.

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I love growing cucumbers from seed, because it’s so exciting when you see the first sign of the new cucumber plant. It’s the joy of being a gardener!

Caring For The Plants

Let’s get to the next stage in our guide about growing cucumber plants from seed, caring for them.

Cucumbers are tough to care for. After germination, they become susceptible to over-watering, drafts and cold weather.

Cucumbers should be regularly watered but only lightly to prevent the base of the plant rotting. With cucumbers, watering is a tough balance, under-watering leads to very weak plants but over-watering leads to rot. Monitor your watering carefully, ideally watering with a small watering can from below rather than a hose pipe or greenhouse sprinklers.

Draughts are probably the biggest killer of cucumber seedlings, so when growing cucumber plants from seed you should avoid this. The easiest way to overcome this is to grow the cucumber in a cloche inside the greenhouse. A cloche gives extra heat but also prevents any sort of draughts or cold air from getting to the delicate plants.

When your cucumber seedlings have 2 or 3 leaves, they can be transplanted to their final locations. Indoors, plant in a pot of good quality (ideally homemade) compost in a pot 30cm (12in) wide and at least 30cm (12 in) deep. This can be done before the last frost. If you are transplanting outside you’ll need to wait until at least 1 week after your last frost date to begin hardening them off to transplant into the garden.

When you put in the effort of growing cucumber plants from seed, you want to make sure they thrive. The best spot for cucumber plants outdoors is a sunny spot that is well protected. Make sure you prepare the ground before planting your cucumbers out. Cucumbers do best in fertile soil, so mix a good amount of well-rotted manure or garden compost into the soil. One to two buckets full of manure should do the job.

Cucumber seedlings are quite vulnerable to transplanting shock, so be careful when you plant them on. To avoid this problem completely, you could use soil blocks. This is a technique where you plant your seed in a compacted block of soil, which can then simply be put in a pot or the bed. To find out more about this, you can read our article about growing in soil blocks.

When growing cucumber plants from seed, soil blocks are a great way to give your young plants the best start in life possible.

Cucumber plant with flowers and fruits

Depending on the variety, a cane or trellis might be required shortly after transplanting.

Once transplanted into their final positions, cucumbers will begin growing VERY quickly (like courgettes which are in the same family). You can often see flowers on the plants just a week after transplanting and be picking your first cucumbers 2 weeks after that.

To make sure you get the most out of your cucumber plants, pinch out the growing tip once the plant has grown seven leaves. Side shoots are ok to leave, but do the same with them, once they have seven leaves.

Once your cucumber plants have started to produce flowers, you need to make sure they have the right nutrients. Feed them regularly, every week is best, with a liquid fertiliser that is high in potash. Tomato feed works great.

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Feeding your cucumber plants regularly will ensure that they will keep growing quickly and produce lots of delicious fruits.

Harvesting Cucumbers

Now we come to the best thing about growing cucumber plants from seed, harvesting the fruit.

Well grown cucumbers crop heavily and quickly. If you are growing a mini cucumber variety, you can expect to harvest a cucumber every other day at the peak of the growing season. Harvesting these cucumbers is simple. Cut the cucumber from the plant with a sharp knife or scissors. Do not pull or twist them from the plant.

Stems that are growing cucumbers may require extra support.

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It’s common that the lower leaves of the cucumber plant will begin to turn yellow and shrivel up in the middle of the season, this is to be expected and just allows the plant to focus on producing new leaves and cucumbers. These yellow leaves can be removed with secateurs once they have died.

Cucumber plants will continue to keep up the strong growth in August and September but will slow down once the weather cools and will usually die after the first frost of the winter.

Pests And Diseases Affecting Cucumbers

No guide about growing cucumber plants from seed would be complete without a mention of pests and diseases to look out for.

Pests

Unfortunately, there are quite a few garden pests that love cucumber plants, including aphids, slugs and snails.

But don’t worry, we will tell you how to deal with these pesky animals.

Let’s start with the gardener’s foe number one, slugs and snails. They have a bad name amongst the gardening community, because they like to eat quite a lot of our garden plants.

However, slugs and snails are vital for our ecosystem, so try to tolerate them where possible. And avoid using any chemicals that will kill them, such as slug pallets.

Slugs and snails love seedlings, so this is the stage when they will become a threat to your cucumber plants. 

slug close up

Growing cucumber plants from seed means you will have seedlings, but they can easily be protected from these slimy customers:

  • Protect outdoor cucumber seedlings by putting a cloche or the top half of a bottle over them. A round wide bottle works best, such as squash bottles. Just cut one in half next time you have finished with it. To be absolutely sure, put some mesh over the bottle opening, to prevent the slugs and snails from getting in. Don’t put the bottle top on, as this will create unhealthy conditions in the bottle. 
  • Companion planting: an organic way to keep slugs and snails off your seedlings is to plant them with plants these pests don’t like. Such plants include sage, rosemary and lavender. To find out more about this gardening method, read our complete guide on companion planting for vegetables in the UK.
  • You can also go on the hunt for slugs and snails and remove any you find on your plants. The best time to do this is about two hours after dusk. Move them to a part of the garden where they can’t do much harm.

Another pest that might affect your cucumber plants is the whitefly. They are similar to aphids, but are tiny white insects with wings. They suck the sap from the stem of the plants and excrete honeydew, which can cause sooty mould to appear. This can cause the plant to die eventually, from lack of light.

Like other insects who eat plants, they can spread plant viruses that could damage your cucumbers.

It’s quite easy to see if you have got a whitefly infestation, when you carefully shake the plant they will fly off, and it will look like a white cloud.

Whitefly thrive in warm, damp conditions, so are mostly a problem in greenhouses. Outdoor cucumbers are less likely to be affected.

But there are things that you can do to minimise their impact:

  • You can buy sticky sheets that you can hang above or around the plants. They are normally yellow and this makes them attractive to the whitefly. It will not do much if you have a heavy infestation, but it will help to monitor the situation.
  • You can introduce a predator to control the pest, for example, Encarsia, which is a small parasitic wasp, which will eat the whitefly nymphs. You can buy them from biological control suppliers.
  • Try to reduce the number of plants the whitefly will like, which includes tomatoes and peppers, in the greenhouse. The fewer host plants there are, the fewer the number of whitefly.
  • Clean your greenhouse in winter to get rid of any whitefly population that is overwintering there.
  • To avoid sooty moulds from getting too bad, ensure your greenhouse is well ventilated.
  • Companion planting: Plants like basil, Nasturtium, chives, onions will repel whiteflies and protect plants that are planted with them. 

Another insect that can affect cucumbers that are grown in the greenhouse are red spider mites.  

red spider mite on soil

They suck the sap of the plants and can cause the leaves to fall off and kill the plant, in severe cases. Red spider mites are not fussy and will feed on a wide range of plants and vegetables, including cucumbers.

The red spider mite likes warm, dry conditions, hence why they like greenhouses. But in hot, dry weather, they can also cause issues outdoors. 

The signs that red spider mites have invaded your greenhouse are pale mottling on the top of the leaves. Under the leaves you might find lots of small yellow-green mites and eggshells. You might need a magnifier to see them.

They are actually not red, even if they are called red spider mites. They are more yellow-green with two dark spots. Some are completely dark. In autumn, though they have a red-orange colour, probably why they got their name.

If you have a heavy infestation, you will see fine webbing on the infected plants. And their leaves will dry up or fall off. 

The good news is that you can do things to prevent damage to your cucumbers:

  • Create humid conditions in your greenhouse, as this will keep the red spider mites away. 
  • Keep your cucumbers and other plants in the greenhouse well watered.
  • Give your greenhouse a good clean over winter, as they can overwinter. 
  • Keep the greenhouse and the soil around it weed-free, as they can act as hosts for the mites.
  • Encourage predatory insects into your greenhouse, such as ladybirds and lacewings. You can buy them from biological control suppliers or just open the doors and windows of your greenhouse and put flowers that attract them in your greenhouse, such as thyme, marigolds, yarrow and dill. 
  • Introducing plants that will repel spider mites can prevent them from becoming a problem. Such companion plants include chives, onion, dill and garlic. Have them around your greenhouse and the mites should keep away.
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Aphids can also attack cucumber plants. They are small round insects that will suck the sap from the stem. 

severe infestation of cabbage aphids

They are big enough to see with the naked eye, so you should spot them easily. Another sign are ants on and around the plant, as they ‘farm’ them. They love to eat the honeydew the aphids secrete.

Here are some things you can do to reduce the harm they cause:

  • Predatory insects like ladybirds, hoverflies, earwigs and ground beetles as well as predatory wasps love aphids. Introduce them into your greenhouse, either by buying them from a biological control supplier or by planting flowers that will attract them and allow them access. Such flowers include marigolds, foxgloves and yarrow.
  • Remove any aphids you spot by hand, if you are not squeamish.
  • Alternatively, you can lay newspaper under the plant and shake it carefully. The aphids will drop off, and you can then remove them.
  • You can also use companion planting to repel the aphids and prevent them from attacking your cucumbers. Plants that will repel aphids include onions, chives, garlic, lavender and marigolds.
  • You can also wash the affected plants with soapy water or commercially available insecticidal soap, such as this.
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Diseases

There are two main diseases that can affect cucumbers and no guide about growing cucumber plants from seed would be complete without mentioning them.

Cucumber mosaic virus is spread by aphids and will stop cucumber plants from growing. It will also affect the yield, as it reduces the plants’ ability to grow flowers and fruits.

A sure sign of this virus is a distinctive yellow mosaic pattern on the leaves. There is no cure, so once you have identified the virus, destroy the affected plant immediately. Then wash your hands with soap before touching any others to avoid spreading the virus.

The only way to keep this virus away is to keep aphids away from your cucumber plants. Just follow the tips above.

Powdery mildew is another disease that can affect cucumber plants. It’s a fungal disease, and you can easily spot it, as it will produce a layer of white powdery mould on the leaves. 

The main cause of this disease is under watering. If the soil is too dry, it can develop on the plants. So it’s easy to prevent:

  • keep the soil moist and water regularly. The best way to water any plant is from below to avoid the foliage from getting wet.
  • Give the plants room to ensure good air circulation.
  • Make sure you weed the bed the cucumber plants are in and keep the area free of plant debris

If you do see any sings, remove the leaves that are infected and destroy them, do not compost them.

Now that we have given you the secret of growing cucumber plants from seed, you will be ready to try it yourself. Soon you can enjoy delicious cucumbers from your garden. Happy growing!

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