When and How to Fertilize Blackberries

Munching on a ripe blackberry is a sensory experience that is hard to replicate: the snap between your teeth then the rush of juice, and the crack of the tiny seeds.

Blackberry bushes are pretty reliable. You don’t need to baby the plants for them to produce an abundant harvest.

A close up vertical image of ripe clusters of blackberries growing in the garden pictured in light sunshine. To the center and bottom of the frame is green and white printed text.

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But fertilizing is one element that you must pay attention to if you want to achieve an abundant crop. Next to pruning, it’s probably the thing that will have the biggest impact on your berry harvest.

We’re going to explain how and when to feed blackberries to make the process easy, so here’s what you can expect coming up:

The hardest part of fertilizing blackberries is probably avoiding the thorns, so don’t stress. Just don some gloves, a long-sleeved shirt, and get ready to jump in.

What Kind of Fertilizer to Use

There are several types of fertilizer out there, from organic options to conventional chemicals. They can all work, so the decision largely comes down to your personal preference.

The easiest option is to use a balanced, slow-release granular fertilizer like a 10-10-10 or a 20-20-20 (NPK), such as Lily Miller All-Purpose Planting & Growing Food, available from Amazon in four-pound bags.

Lily Miller All-Purpose Planting & Growing Food

Liquid fertilizer can also be used, but will need to be applied more frequently and is a more expensive option.

If you do wish to go this route, you can either use a 3-3-3 (NPK) or use a 10-10-10 such as Bonide Liquid Plant food, diluted by half.

A close up vertical image of a bottle of Bonide Liquid Plant Food isolated on a white background.

Bonide Liquid Plant Food

You can find Bonide Liquid Plant Food in eight-ounce bottles available via Amazon.

However, if you generally try to avoid using chemicals in the garden or you just like to take a more natural approach, well-rotted manure also works well.

A close up vertical image of two gloved hands from the right of the frame picking up well rotted manure to use as plant food.

You just need to be sure you apply it in the fall so it has time to work into the soil and for any salts to leach out.

When to Fertilize

Figuring out when to feed is easy. If you’re using commercial fertilizer, feed your plants once per year with a balanced, slow-release granular fertilizer when the blackberries are mid-bloom.

A close up horizontal image of white blackberry flowers growing in the garden with foliage in soft focus in the background.

If you are using liquid fertilizer, you’ll need to apply a 3-3-3 (NPK) three different times: when the leaves bud, when the flowers bud, and when the berries start to change color.

A half diluted 10-10-10 (or 5-5-5) should be applied twice: when the leaves bud and when the flowers are fully formed.

If you’re using manure or compost, apply it in late fall before the first projected frost date.

Now, there is an exception to these rules.

If you start to notice that the coloring of the leaves is a little pale, test the soil and address the problem according to the results of your test right away. Don’t wait for the next scheduled fertilizing time.

How to Fertilize

Before you start your feeding routine, it helps to test your soil. You might find that you have adequate levels of nitrogen, and you don’t even need to bother feeding that year.

A close up horizontal image of a gardener applying granular plant food around young blackberries.

You might also discover that your soil has the wrong pH, and you’ll need to do some adjusting so that the food will be accessible to your plants. Blackberries prefer a slightly acidic to neutral pH of 5.5 to 7.0.

After the first year, you won’t need to continue testing unless you are adjusting the pH. Otherwise, you can assume that your plant is using up the available nitrogen in the soil and you need to replace it.

The nice thing about fertilizing blackberries is that it’s all about nitrogen. You don’t have to worry about balancing all the other nutrients. Just nail the nitrogen with a balanced fertilizer or well-rotted manure and you’re good.

New Plantings

New plantings need special feeding.

The general rule of thumb is that one-year-old plants need one and a quarter ounces of nitrogen per linear foot. That comes out to about five pounds per 100 linear feet of 10-10-10 granular fertilizer.

You can also apply the food in a circle around the plant. Use three quarters of an ounce of 20-20-20 or one and a half ounces of 10-10-10 fertilizer around the dripline.

A close up horizontal image of two gloved hands from the left of the frame planting out a small seedling.

Two-year-old plants need about one ounce of 20-20-20 or two and a quarter ounces of 10-10-10  per plant.

To be extra safe, apply half of the required amount in the spring after the leaves have formed and the other half after the blossoms have fully formed.

Established Plants

For plants that are three or more years older, use a 20-20-20 mix and apply one and a half ounces in a circle around each plant. The fertilizer should be applied at or just inside the drip line.

If you’d rather, you can also use a 10-10-10 fertilizer at three ounces per plant.

A close up horizontal image of young blackberry shrubs with manure applied in fall.

If you have a row of blackberries, you can also apply the fertilizer in a row rather than around each plant. You want to apply about 10 pounds per 100 linear feet of 10-10-10 fertilizer.

If you know you have fairly healthy soil with a good balance of nutrients – which is why testing is key – you can side dress each plant with several handfuls of well-rotted manure instead of using commercial fertilizer.

Feeding Blackberries for an Abundant Harvest

It’s easy to get swept up in caring for the rest of your garden and forget about the less fussy plants like blackberries.

But don’t neglect the key maintenance chores like fertilizing. It makes such a difference. It doesn’t require much time, and hopefully, this guide has given you the info you need to finish the job even more quickly.

A close up horizontal image of ripe blackberries growing in the garden pictured on a soft focus background.

Let us know in the comments if you run into any problems with the process. We’re happy to help you sort it all out!

If you want to expand your knowledge of growing blackberries, we have a few other guides that might grab your fancy, including:

Photo of author
Kristine Lofgren is a writer, photographer, reader, and gardening lover from outside Portland, Oregon. She was raised in the Utah desert, and made her way to the rainforests of the Pacific Northwest with her husband and two dogs in 2018. Her passion is focused these days on growing ornamental edibles, and foraging for food in the urban and suburban landscape.
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