Kale – Sun, Water, And Soil Requirements


Kale is part of the Brassica family and is regarded as a winter vegetable. It’s easy to grow, and you can continually harvest the leaves all throughout even the coldest months.

Kale happily grows in full sun but can handle partial shade, especially in climate zones that experience hot summers. It also likes to be kept moist but doesn’t handle waterlogged soils. The soil should be well-draining, open, and friable. Kale will tolerate slightly acidic soil that includes plenty of organic matter such as compost.

Let’s go into more detail about the ideal growing requirements for kale.

Does Kale Need Sun Or Shade?

Kale needs at least six hours of sunlight daily to produce a lot of new growth. If your kale does experience less daily sunlight during the day, it will produce fewer leaves but will still grow quite well.

How much sun kale needs depends on your climate zone and the growing conditions that you provide. Kale is regarded as a cold-weather plant, much like other Brassicas such as cauliflower, broccoli, brussels sprouts, and cabbage.

Primarily, it will produce a lot of lovely, tender green leaves if the temperature is under 75 degrees Fahrenheit (24 degrees Celsius). This means that it grows best in USDA zones 7 to 10 because it will continue to grow during the winter months, and the leaves will even be sweeter if they’re exposed to a little frost.

Along the same lines, if your summer temperatures don’t rise above 75 degrees Fahrenheit (24 degrees Celsius), then you can grow kale in full sun even in summer. In this case, your kale plants should produce lovely new leaves to keep you fed all through the spring, summer, and fall, as well as the winter.

If you live in a climatic zone where your summer temperatures reach closer to 100 degrees Fahrenheit (38 degrees Celsius), then you should definitely plant your kale in part shade. The ideal situation here would be to expose your plants to a little morning sunshine but to keep them protected from the hot midday and afternoon sun.

This means that you can grow kale successfully even if you live in a sub-tropical climate. You just have to ensure that you protect the plant from the extreme heat experienced during the day.

Why Does Kale Not Like Hot Afternoon Sun?

The answer to this goes back to the fact that kale is regarded as a winter vegetable and is quite cold tolerant. If the plant is exposed to too much hot midday and afternoon sun, it is likely to trigger the plant’s bolting mechanism.

When this happens, the plant thinks that it’s near the end of its growth cycle and will start the reproduction cycle. This means your kale will start producing flowers and, eventually, setting seeds.

So, as you can see, if you give kale some shade from the afternoon sun, it will continue to grow and produce more of those lovely green leaves. This should allow you to extend the harvesting season of your kale.

Here’s a quick chart to explain this further.

Daytime TemperaturesSpringSummerFallWinter
Below 75 degrees Fahrenheit (24 degrees Celsius)Full SunFull SunFull SunFull Sun
Above 75 degrees Fahrenheit (24 degrees Celsius)Full SunPartial ShadeFull SunFull Sun

 How To Provide Shade For Your Kale 

If your summer temperatures get higher than 75 degrees Fahrenheit (24 degrees Celsius), then you’ll want to provide some shade for your kale during the afternoon. This can be done in a number of ways.

If you have deciduous trees in your yard, you can plant your kale in a spot where the trees will cast some shade in the afternoon in the middle of summer. This is ideal because the trees will have no leaves in the cooler months and will let the sunshine through.

Another thing you can do is create a shade structure for your kale. This could simply be a frame with some shade cloth draped over the top. Position this in such a way that the morning sun gets through, but your plants are shaded from the heat of the afternoon sun.

Alternatively, you can grow your kale in pots. This is one of the better solutions because you can easily move the pots around your garden. You can place your container-grown plants in full sun during fall, winter, and spring and then move them into the shade in summer.

In this way, you’ll be able to extend the harvest of your kale leaves for much longer.

So, to summarize, kale should be grown in full sun in cooler climate zones that don’t experience hot summers. However, if you live in a warm zone and your summer temperatures are hot, plant your kale so that it receives some shade, at least in the middle of the day and the afternoon.

How Often Should I Water Kale?

Kale, like other leafy vegetables, requires a fair amount of water to thrive and grow.

You should give your kale plants around 1 to 1.5 inches of water every week. This equates to around 1 gallon of water per square foot of soil (4 liters per 30 square centimeters).

To understand why you have to look at the structure of the plant. Kale has lots of large, tender leaves. This large leaf area means that the plant will transpire a lot more moisture, especially as the temperature starts to rise.

All this loss of moisture has to be replaced to ensure that the plant gets enough water to survive and grow. So, in the warmer weather, it’s important to water your kale almost daily, especially if your area doesn’t receive a lot of rain.

However, it’s also important not to overwater your kale either. You see, the plant does not like to live in overly soggy soil. The ideal is to keep the top few inches of soil moist as much as possible.

If you find that you have trouble determining just how moist your soil is, you can easily purchase a moisture meter at your local hardware or garden supply store. This will allow you to check the moisture level and ensure that your plants are getting the water that they need.

It’s also a good idea to keep an eye on your plants during the day, especially in summer. If you see the leaves start to droop, it means that the plant is lacking in moisture. In this case, it might also be a good idea to provide some afternoon shade for your kale plants.

Mulching Your Plants Will Keep The Moisture In

One of the best ways to keep your kale plants nice and moist is to apply a good layer of organic mulch. You can use either compost or, even better, a layer of quality composted hay. This will ensure that the moisture won’t evaporate from the soil, and it will keep the soil cooler too.

Another benefit of mulching is that eventually, the mulch will break down and release valuable nutrients into the soil. These nutrients will then be available to your kale plants and will keep them growing strong.

Set Up An Automatic Watering System

Another way to ensure your kale is getting enough water is to set up an automatic watering system. This means you won’t have to get out with the hose or watering can every single day in the warmer months.

For most vegetables, a drip system is best because it applies water directly to the roots of the plants and avoids getting the leaves wet. This is especially good if your area is susceptible to fungus diseases.

A drip system is easy to install too. All you need is a length of poly pipe that attaches to an outdoor tap. Then you want some lengths of thinner tubing, one for each plant. You push this tubing into the poly pipe with special clips. Finally, you attach a dripper to each of the smaller pieces of tubing and position these at the base of each of your kale plants.

You can even go one step further and purchase a timer that attaches to your tap. This way, you can set the timer to turn on the watering system for around 10 to 15 minutes every day during summer. 

Be sure to check the water level of the soil around your plants on a regular basis to ensure that they’re getting enough water but not too much. Then, you can adjust the watering schedule accordingly.

Best Soil For Kale

Kale is no different from most home-grown vegetables. It prefers well-drained soil that contains a fair amount of nutritious organic matter.

The soil pH level for kale should ideally be around 5.5 to 6.8, which is slightly on the acidic side. However, kale will generally tolerate soil that is a little more alkaline.

To prepare your soil for planting, you should incorporate plenty of organic matter first. You can use your own homemade compost, or you can add in some organic animal manures mixed with dry leaves, grass clippings, and even composted hay. A bone meal is also a good addition to the soil.

Remember, you want the soil to be relatively friable and not too compacted. Vegetables, like kale, need air pockets in the soil so that the roots can easily take up water and nutrients. Compacted clay soil does not have enough air pockets, and therefore, your plants may suffocate.

If you do have very heavy clay soil, then you have to work on improving it before you plant out your kale. You can do this by incorporating lots of organic matter into the soil.

Another option is to plant your kale in containers. This way, you can control exactly the type of soil that you use. Make sure you choose a good quality potting mix, and remember that plants grown in pots will dry out much faster than those grown in the ground.

Therefore, you have to ensure that you establish a regular watering regime to keep your plants well hydrated.

How To Determine And Adjust The pH Level Of The Soil

As mentioned, kale prefers slightly acidic soil around the pH level of 5.5 to 6.8 but will tolerate slightly more alkaline soil.

To test the pH of your soil, you can purchase a do-it-yourself-kit from a garden supply store. Otherwise, you can send off a soil sample to a laboratory that specializes in soil testing.

If you find that your soil is too acidic (below 5.5), you can easily incorporate some lime into the soil. Poultry manure is also good for adding some alkalinity to highly acidic soil.

On the other hand, if your soil is too alkaline (above 7), you can easily improve the acidity by adding plenty of organic compost or animal manures. You can also add some leaf litter to your soil to increase the acidity.

What Fertilizer Is Best For Kale?

Being a leafy green vegetable, kale will prefer plenty of nitrogen as this promotes leafy growth. It will also need a balanced amount of phosphorus and potassium to encourage strong root growth. Remember, it’s the roots that feed the rest of the plant.

To determine the makeup of the fertilizer that you want to use, you have to look at the set of three numbers that appear on the pack. These three numbers indicate the ratio of nitrogen to phosphorus and potassium.

For example, a fertilizer pack that has the numbers 10-8-8 will contain 10% nitrogen, 8% phosphorus, and 8% potassium. For kale, you’re ideally looking for a fertilizer that has an equal balance of all of these, such as 10-10-10.

Because you’ve added composted, bone meal, or animal manure to the soil before you planted the kale, this should keep the plant going until the roots are fairly established.

You then want to apply a small amount of fertilizer just after you’ve harvested the first set of leaves. This will give the plant an extra boost to continue to keep growing more new leaves. If you use a slow-release type fertilizer, your plants will continue to receive the nutrients that they need over an extended period of time.

It’s important to remember not to over-fertilize your plants. An excess of fertilizer can easily be leached from the soil and end up in the natural waterways near where you live.

Just let the plants tell you what they need. If the leaves are growing and are looking nice and green, then the plant is getting enough nutrients. However, if the new growth shows some signs of yellowing, then it’s time to give your plants some extra food.

Greg

Greg has been interested in homesteading for years. He produces part of his food by himself. And tries to live the most sustainable lifestyle he can.

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