Biting into a cool cucumber straight off the vine in the summer’s heat – that’s the vegetable gardener’s dream. But while cucumbers are supposedly an easy vegetable to grow, they have very exacting needs, including the amount of sunlight they get.
Cucumbers will struggle if grown in shade. They grow best when they get at least 8 to 10 hours of direct sunlight per day, but can still grow well if they get at least 6 hours. The less sun a cucumber plant gets, the fewer cucumbers you’ll get. Light shade (like dappled leaf cover) is better than heavy shade.
However, it’s important to remember that while cucumbers are a heat-loving vegetable, if temperatures rise above 90F or 30C for more than a couple days, they will drop their blossoms or grow stunted cucumbers.
For gardeners in USDA Hardiness Zones 9 – 12, it may seem impossible to grow cucumbers. But long periods of high heat is the one case where it’s better to grow cucumbers where they’ll get some shade throughout the hottest part of the day.
You also need to be careful about huge spikes in sunlight exposure. If you grew seedlings indoors, you’ll need to harden them off, gradually getting them used to getting more intense sunlight throughout the day. Lower leaves and cucumbers suddenly exposed to a lot more sunlight can burn.
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Can Cucumbers Grow In Shade?
Cucumbers can’t grow in total shade. Few vegetables can. They can tolerate partial shade, so long as they get 6 hours of sun per day, but they grow best when they get at least 8 hours.
If they don’t get enough sun, then the cucumber plant will:
- Produce fewer, shorter, bitter cucumbers. A plant needs to photosynthesize (taking sunlight and turning it into energy) to live and grow, and producing fruit is the most energy-intensive process. Without adequate sunlight, a cucumber plant may survive, but it won’t have enough energy to blossom and grow fruit. The plant will put all of its resources into growing more vines and leaves to reach more sunlight. If you get fruit, they’ll taste bitter.
- Get yellow leaves. Chlorophyll (the thing that makes leaves green) is a byproduct of photosynthesis. If the cucumber plant can’t photosynthesize enough because it doesn’t get enough sun, then the leaves can’t produce chlorophyll, and the leaves will turn yellow. But lack of sunlight isn’t the only issue that causes yellow leaves. Yellow leaves may be caused by a lack of water, soggy soil, and/or nutrient deficiencies.
- Produce fruit with a shorter shelf life. Did you know that chlorophyll concentration also affects how long fruits and vegetables can last? With lower light levels, cucumbers have less chlorophyll, and so they’ll go bad sooner.
- Be prone to insects and disease. Cucumbers are already prone to insects and disease, and a poorly growing plant is even more so. A lack of sunlight may mean that leaves dry too slowly and diseases will take advantage. Your best defense against both is always a healthy, thriving plant.
How Much Sunlight Do Cucumbers Need? (Hours Per Day?)
Cucumbers need at least 6 hours of full sun per day. To grow its best, it needs between 8 and 10 hours.
The more light a cucumber plant gets, the more vigorously it’ll grow and produce. However, you don’t need those 8 to 10 hours to be consecutively.
Also, not all shade is equal. Some shade is heavy, like under thick canopy cover or under buildings, while other shade is lighter, like the dappling shade of a tree. The lighter the shade, the more light still reaches the plant even under shade cover.
Can Cucumbers Get Too Much Sunlight? What are the problems?
Yes, cucumbers can get too much sunlight, although the bigger problem is too much heat. (But more on that below.)
Plants need a period of darkness to grow well. Nighttime helps them regulate different functions, like when to bloom, set seed, or lose leaves.
As a day-length neutral plant, cucumbers aren’t tied to the length of darkness, but they still need it. This is why horticulturists advise that you only leave on grow lights for 16 hours per day.
If a cucumber plant or fruit goes from a low light to an intense light situation, then you get sunscald. Sunscald happens to any fruit or vegetable when they suddenly get more intense light than they’re used to. That’s why we harden off seedlings by gradually exposing them to longer periods of intense light before transplanting them.
Sunscald also happens when you cut back leaves to expose previously shaded leaves and fruit, or if you harvest cucumbers from under leaves and leave them out in the sun. If you’re growing on a trellis and the cucumbers are regularly exposed to light, sunscald is much less likely.
While cucumbers are heat lovers, they prefer when it stays below 90F (30C). Above that temperature, and they’ll develop a number of problems, including:
- Dropping blossoms. After a few days of high temperatures, blossoms will fall off the plant. No blossoms mean no fruit.
- Bitter fruit. The heat will suck out all the moisture from the soil much faster, leaving soil drier and cucumbers thirsty. Cucumbers only have short little roots that can’t reach lower below ground where moisture may remain. When cucumbers don’t get enough water, their fruit tastes bitter.
- Lower pollination rates. Many species of bee prefer temperatures between 60F and 90F, and once it gets above that, bees move slower and pollinate fewer flowers. Cucumber’s small flowers aren’t very attractive to bees. Not a problem when bee activity is high, but when bees need to slow down, they’ll target better options first. You may need to hand pollinate.
- Misshapen fruit. Even when bees pollinate cucumbers, they may not pollinate them enough. Not enough pollination leads to misshapen fruit, like cucumbers curved into a C shape, with one end bigger than the other, or both ends bigger than the middle.
If you’re in USDA Zones 1 – 8, you may just need to wait out the heat wave or install temporary shade cloths.
Shade cloths lower the temperature, provide UV protection, and reduce water evaporation by shading the plants and soil. Unlike a row cover, which arches over the plants providing complete cover, you only need to cover above the plant. This allows sun to reach the cucumber plants during the cooler hours while providing shade during mid-afternoon.
While you can use an old sheet as a DIY shade cover, you’ll want one that’s thin enough to allow some light to get through. The best shade cloth for cucumbers has a percentage between 30 to 50%.
If you’re in USDA Zones 9 – 12, then you already know you’re going to get long periods of heat through the long summer months. So plan ahead and plant your cucumbers where they’ll get part shade during the afternoon when it’s hottest, but full sun during the morning and evening. The best spots also allow cucumbers to get more sun on the shoulder seasons, when it’s still warm enough for cucumbers to grow.
To provide temporary shade, you can plant a veil of corn or sunflowers in front so that they’ll grow tall during the summer heat, or use a shade cloth.
How To Get More Sun For Cucumber Plants
If you’re struggling to find the right place for your cucumber plants, here are a few tips:
Make a sun map
The first step to knowing where to plant your cucumbers is to figure out where the sun is going to be in your garden throughout the summer. A sun map is a map of your property with shaded areas showing where you get full sun, part sun/part shade, and full shade.
- Make a map of your property. All you need is a piece of graph paper. The graph will help with scale. Then draw in any obstacles, like trees, buildings, and fences, and where your current garden is.
- Make 5 copies (or 6 with one extra in case of mistakes). Having more copies will make things easier when drawing in shadow lines at different times of day. And if you make a mistake, you always have another copy.
- Mark shadows on the maps throughout a sunny day. Crosshatch in shadows where they fall at 9:00, 12:00, 3:00, and 6:00. This timing doesn’t need to be exact, but stagger it throughout the day.
- Estimate the sun angle and shadows through the year. If you don’t live at the equator, then the angle of the sun changes throughout the year. The best time to make a sun map for cucumbers is in the middle of the summer, but if you can’t, then try to estimate it. Shadows will be shorter in mid-summer, and longer in the spring and fall.
- Compare the maps for the final copy. Mark areas as sunny if at least 3 maps show it to be sunny, and shady if at least 3 maps show it to be shady. If an area doesn’t reach 3 sunny or shady maps, then it’s part-sun or part-shade.
- Update the map throughout the growing season. Your final copy should give you a good idea of where the sun is, but as you go throughout the growing season, you may find mistakes or changes. That tree may put off more shade than you thought, or someone added a new structure.
Finally, it’s always a good idea to keep a planting map on hand and keep notes throughout the growing season. That way you can make note if where you planted your cucumbers is actually a good spot or if you should switch it up (and where). In the midst of the growing season, we often think that of course we’ll remember things, only to draw a blank when it comes time to plan next year’s garden.
If you’re not a note-taking/records kind of person, then take photos throughout the season. Use wide shots to get an idea of where you planted things and close-ups to see the health of the plants.
Grow on a trellis
After sufficient watering, trellising is the best thing you can do to grow abundant cucumbers. By lifting the vines off the ground, you’ll give the leaves more access to sunlight (as well as reduce disease, pests, and rotting fruit).
Even bush cucumbers benefit from a shorter trellis. A lean-to trellis will help the lower leaves get more light than a vertical trellis.
Angle the trellis to the sun
For the most sun, angle your trellis so it’s facing south. If that’s not possible in your garden setup, then try to face the cucumbers to the east. The morning light will dry off leaves from morning dew or overnight rainfall.
If that’s not possible, then angle to the west. Angle arches and a-frame trellises east and west so each side gets direct sunlight.
Prune lateral runners
Cucumber vines need to be pruned just like tomato plants, especially when growing on a trellis. The main stem has nodes which grow a leaf, a fruit, a tendril, and a lateral runner.
Just like a tomato plant, prune the lateral runners. Clean your garden shears before pruning to prevent spreading disease. Don’t cut the main stem or the cucumber vine won’t be able to grow.
Bush cucumbers don’t need pruning like vines do, but if you notice that leaves are starting to shade out other cucumber plants, then trim them back.
Consider the full height of plants growing in front of cucumbers
Adding a vertical trellis at the north end of a garden bed makes sense, as you can use the rest of the garden bed for another plant. Just keep in mind the full height of growing plants.
People recommend sunflowers or corn as companion plants, but they can grow very tall. They are great if you need to provide heat protection during the summer, but unhelpful when you have a shorter growing season.
Lower planting density
You can fit a lot of cucumber plants on one trellis, but that doesn’t mean that you should. More plants means more leaves.
Crowded leaves will shade out other leaves. The bigger the leaf of the cucumber variety you’re growing, the less densely you should plant.
Grow in movable containers
If you have a really small garden, can’t find a single location that gets enough sun throughout the summer, or aren’t sure of the sun exposure, then plant bush cucumbers in containers. You can then move them around the garden. This is a great way to experiment with placement.
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Conclusion
The more sun a cucumber plant can get, the more it’ll produce, but it still needs a period of darkness at night. You can still plant in lower light conditions (except for heavy shade), but you just won’t produce as much.
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~Jonathon