How to grow cucumbers, and why they turn bitter

Why a cucumber goes bitter

The bitterness is a compound the plant makes more of when it is under stress, and the 2 things that stress a cucumber hardest are heat and uneven watering. So a plant that gets a big drink on Saturday, nothing until Wednesday and then a heatwave in between will give you bitter fruit even though nothing about the variety or the soil has changed. The bitterness concentrates at the stem end and just under the skin, so a bad one can often be rescued by cutting the end off and peeling it, but the real fix is upstream.

That is worth saying plainly because most people assume they bought the wrong seed. It is nearly always the watering.

Pick a variety that suits where it is going

• Lebanese. Short, thin skinned, no peeling, and the one most people actually want for salads.
• Long green or continental. The classic slicer, longer fruit, happiest climbing something.
• Pickling types. Small and bumpy, bred to stay crisp in a brine.
• Bush or patio types. Short vines for a pot or a small bed, where a sprawling variety would take the lot.

Wait for warm soil, not for a date on a calendar

Cucumbers sulk in cold ground and a seed sown into it will often just sit there and rot rather than germinate. The practical test is to put your hand flat on the soil in the morning. If it feels cold rather than cool, it is too early. Starting seed in pots somewhere sheltered and planting out once the nights have genuinely warmed gets you a few weeks ahead without the risk.

The bed wants to be loose and full of organic matter and it wants to drain, because a cucumber will not tolerate sitting in water any better than it tolerates drying out. Compost or aged manure dug through before planting does most of that work.

Water deeply and on a rhythm

Deep and regular beats little and often, every time. A long slow soak that gets water well down encourages roots to follow it, and a daily sprinkle keeps the roots at the surface where they cook. Mulch is the other half of this, because it stops the surface drying out between waterings and it is the single cheapest thing you can do to stop the bitterness. On a hot week, check rather than assume.

Get them off the ground

Cucumbers climb given anything to climb, and a trellis or a few stakes and some twine will do it. Growing them up rather than along keeps the leaves dry, which cuts the mildew problem right down. It also keeps the fruit straight and clean and makes them far easier to find, because a cucumber lying under a leaf is invisible until it is the size of a rolling pin.

Feed for fruit, not for leaves

Too much nitrogen gives you a magnificent vine with very little on it. Once the plant is flowering, a feed with potassium in it is what pushes fruit rather than foliage, and a liquid feed every couple of weeks through the productive stretch keeps it going rather than letting it exhaust itself.

The pests you will actually see

Aphids gather on the growing tips and whitefly turn up once it is humid. Snails and slugs go for the young seedlings, and caterpillars arrive later on. Start with the free options, which means knocking aphids off with a sharp jet of water and going out at dusk with a torch for the snails. Where that is not enough, a horticultural oil or a pyrethrum spray will handle the sap suckers, and both are gentler than the heavy stuff. Spray late in the day rather than in the middle of it, so you are not hitting bees and not burning leaves.

Powdery mildew is the other one, and it is a watering problem before it is a spray problem. Water the soil rather than the leaves, give the plant room for air to move through it, and pull off the worst affected leaves rather than leaving them there to seed the rest.

Pick often, and pick young

A cucumber left on the vine tells the plant its work is done, so the plant slows down. Take them while they are still on the small side and check every couple of days in the warm weather, because they go from perfect to enormous faster than anybody expects.

None of this is specialist knowledge, and plenty of people who have been growing vegetables for years still get a bitter one and blame the seed. Same answer for everybody, whether it is your first season or your thirtieth.

Shop related products

• D.T. Brown Cucumber Lebanese Seed. The short thin skinned one, and the one most people mean by cucumber.
• D.T. Brown Cucumber Long Green Seed. The long slicer, best grown up a trellis.
• Martins Organic Sugar Cane Bale 11kg. Mulch, which is the cheapest fix for bitterness there is.
• Multicrop EcoPest Oil Insect Spray. A horticultural oil for aphids and the other sap suckers.
• Brunnings Potash Power 2.5kg. Potassium, for a plant that is making leaves instead of fruit.

Did you know we also stock trellis panels in several sizes, garden stakes, jute and sisal twine, snail pellets and watering cans in store. Most of that is not on the website, so give us a ring on (08) 8536 4333 to check what is on the shelf.

The seed rack, the sprays, the bagged mulch and the seed raising mix all live in the garden centre, and the online range is in garden products. The sprays sit in pest control if you want to compare them.

Read next

• When to pick vegetables, crop by crop
• How to keep a garden green on less water
• When a garden pest is worth spraying, and when it is not

I still let half of mine sprawl along the ground, and I still know better.

Cheers,
Candeece