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Have you found yourself puzzled over the question: why are my cucumbers turning yellow?

It’s not unusual for a few cucumbers to be lost each harvest, but if you’re consistently growing bitter tasting cucumbers, there’s a few things to know to prevent the discoloration that causes the bitter taste from yellow cucumbers.

Yellow cucumbers are a problem for gardeners of all experience levels. The yellow pigment of cucumber plants is called cucurbitacin and the causes can include:

  • Over-watering – not always in your control
  • A lack of fertilizer or the wrong type
  • Cramped growing conditions
  • High temperature fluctuations

The first thing that’s likely to affect the cucumber plant is the spacing it has to grow. For any bushing variety of cucumber plant, they need plenty of space for the vines to fan out.

When the grow conditions are cramped, air circulation is decreased. It’s that problem of air flow that leads to over-watering because just one heavy downpour without good air flow due to plants being too close together will affect the time it takes for them to dry out.

The soil is important too as it needs to be well-draining. If your garden soil is the clay-type, soil amendments such as adding sand, organic matter and compost can help improve drainage.

The ideal pH levels for planting cucumbers is 6.0 to 7.0.

Getting the Spacing Right

When planting cucumbers, whether you’re growing pickling cucumbers or any bush variety, the spacing requirements needed differ depending on your method of growing.

If you’re growing in the ground or in containers at ground level, bush varieties need to be planted 3-feet apart. The only way to increase yield by planting closer together is to grow cucumbers vertically using a trellis support.

Cucumbers being grown vertically can be planted closer using a minimum distance of 1.5 ft spacing.

That’s because as they grow higher, and are supported by the trellis along with greenhouse clips to attach the stem to the nylon netting, air is still able to circulate more efficiently, which help the vines to dry out faster than those at ground level would be able to.

Sun Requirements and Watering Frequency

Cucumbers love sunlight and prefer more direct sunlight than most plants. Six to eight hours of full sun daily is needed, but if you live in an area that gets more than 8 hours of full sun daily, take advantage of it. Cucumber plants fruit like crazy when they get longer in direct sunlight.

Naturally, the more sunlight the plants get, the more frequently they’ll need to be watered. Most areas do well with a twice-weekly watering frequency.

Best practice is to wait until the soil is near dry to around 3-inches deep into the soil, then water early in the morning, ensuring the water reaches a depth of 3-inches at least.

The reason you need to be an early waterer with cucumbers is because they detest standing water so by watering early in the morning, by midday when temperatures are increasing, it gives the plant the best chance to absorb nutrients while the higher temperatures contributes to drying out the soil faster.

Fertilizer Requirements

The most common cause contributing to cucumbers turning yellow is a lack of nitrogen. If yellow cucumbers are a consistent problem, this is a likely culprit.

Ideal fertilizers are those with higher levels of nitrogen as opposed to a balanced fertilizer. If you’ve been using a 10-10-10 or similar fertilizer on your cucumbers, it is likely they’re lacking the nitrogen needed to thrive.

The best fertilizers for cucumbers have a NPK of 10-7-7 or 7-5-5, indicating they have a slightly higher level of nitrogen than phosphorus and potassium. All are important nutrients for cucumbers, but they need more nitrogen.

For cucumbers affected by yellowing and stunted growth, that’s a sure-fire indication of nitrogen deficiency.

The fix for this is use up to two tablespoons of 6-10-10 fertilizer per hill of plants when planting your cucumbers, then a top up of 33-0-0 ammonium nitrate mixed into the soil one week after the first flowers bloom and then again three weeks later. Be careful not to add too much fertilizer as that can prevent the plant from fruiting.

When to Pick Your Cucumbers

A key factor to preventing cucumbers turning yellow is knowing when to pick them. By the time they turn yellow, they are wasted because they become over-ripe. These are fast growers that only take between 50 to 70 days from plant to harvest, but some will ripen faster than others.

Regardless whether you’re growing the pickling varieties or slicing cucumbers, they need to be picked early before they turn yellow. Size and color are indicators you can use to know the best time to pick your cucumbers so you can get them when they have the best taste and nutritional value.

For slicing cucumbers, those are best picked when they’re between 7 and 9 inches in length, although most growers won’t let them grow past 8-inches long.

If you’re growing pickling cucumbers to make a sweet pickle, or for gherkins those are best picked when they’re just 2-inches in length. The burpless cucumber varieties should be picked when they’ve reached just 1.5” in diameter.

The larger cucumbers grow, the more chlorophyll fades causing the cucumbers to turn yellow or take on an orange tint and the taste becomes more bitter the larger they get. This is why these should be picked when they are immature, meaning before they grow to the full potential size.

As these are fast growers, during the growing season, expect to be picking cucumbers every other day.

Pests and Diseases that Contribute to Yellowing Cucumbers

Powdery Mildew

Powdery mildew is a fungal disease that covers the vines in a fungus which limits photosynthesis, affects the plant’s growth and chlorophyll production ultimately leading to the cucumber turning yellow. The best method of prevention is to water the soil and do your utmost to keep the foliage dry.

As powdery mildew is a fungal disease, they thrive on wet foliage. This is why air circulation and well-draining soil is imperative to grow healthy cucumbers.

The increased airflow from vertical growing is why it’s a preferred method for growing cucumbers.

Bacterial Wilt, Often Caused by the Cucumber Beetle

The cucumber beetle tends to feed on the vines but they can also leave scarring on cucumbers. The biggest threat of the cucumber beetle isn’t the visible damage to the vine. The damage you’ll notice on the foliage is usually yellowing leaves, wilting stems and holes in leaves.

These don’t always cause a problem to the cucumbers themselves, however, the biggest threat of the cucumber beetle is that they transmit bacterial wilt, which is a bacterial infection that will kill the cucumber plant.

Once a cucumber plant is infected with bacterial wilt, there’s no recovery. It will die and it will need to be removed to prevent the spread of the bacterial disease to other cukes and plants in the cucurbit family which includes cucumbers, squash, pumpkins and green beans. The disease can set in fast, causing severe wilting within just days of infection.

If you suspect your plants are wilting due to a bacterial disease, take a cut from a wilted stem, touch the base where you cut the stem open and if you see thin, thread-like strands between your finger and the stem as you pull your finger away, that’s bacterial wilt and the plant needs to be removed to prevent the spread of infection.

Cucumber beetles are a common cause of bacterial wilt. An effective defense is to use row covers over your crops.

Another alternative that can be effective is to use yellow sticky traps planted just above the tops of the plants. The downside to sticky traps is it can also have the negative effect of trapping pollinators, but the cucumber beetle is more attracted to yellow than most other good bugs.

You can also try inter-planting yellow plants among your cucumbers, or around the borders to fool the beetles into feeding on those plants instead.

When inspecting your cucumbers, these are mostly seen in mid-April time when they come out of hibernation. A pair of yellow gloves with a coating of some petroleum jelly on them are an effective way to remove the beetles by hand before they get a chance to infest the plant.

The Cucumber Mosaic Virus (CMV)

The Cucumber Mosaic Virus only gets its name because it was first identified on a cucumber plant. The virus attacks a wide variety of plants and not just fruiting species, but can even infest weeds.

Aphids are the most common source of CMV transmission so the most effective prevention method is to focus on aphid control which can be done by planting plenty of nectar producing flowers to attract predator insects such as hoverflies, ladybirds and lacewings.

If you’re garden has been affected previously by any viral disease, a horticultural fleece and insect nets can also help prevent CMV.

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