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Fertilizing Rhubarb: When, How & Which Fertilizer To Use

Rhubarb is known for its sour taste and quite thick stems. To soften the flavor, it’s frequently cooked with sugar. The stem is vibrant red or pink and light green goes all the way up in the leaves.

Rhubarb is a perennial in the Polygonaceae family and the leaves are considered poisonous because of the high concentration of oxalic acid mentioned by the Food Science Extension Specialist Professor Dr. Barbara H. Ingham.

Rhubarb is a bitter plant, but it’s interesting when it’s cooked, the vegetable takes a different direction from bitter to sweet. It’s kind of like a life lesson, there’s sweetness in everything.

Some people like to eat it raw, and yes it’s ok especially when it’s sliced thinly, it gives hints of sugar and mellow flavor.

Thankfully, rhubarb doesn’t require too much fertilization and is an easy-to-take kind of plant. Let’s find out more about the topic. 

When to Fertilize Rhubarb?

 Rhubarb is a perennial plant and only twice a year asks for fertilization. The first fertilization should happen in the Spring time and the second one in the Fall.

You can use all-purposed fertilizers with one condition, in the NPK ratio, the product has to be rich in nitrogen in the spring fertilization, and in the fall fertilization, it should be rich in phosphorus.

In case you have planted rhubarb in containers or gardening beds, during the growing times, you can increase the fertilization to 3 times a year.

How to Fertilize Rhubarb?

As I said 2 times in year fertilization is fine for rhubarb will feed the plant perfectly fine.

 According to The U.S. Department of Agriculture (USDA), 1.2 cups of all-purpose application with a 10-10-10 ratio all around every plant should be ok. Apply lightly and try not to touch the crown. Various types of soil, need only nitrogen after using the complete plant food for about 4-5 years.

Apply manure as a principal source of fertilizing approximately 2-3 inches layer in the soil around the rhubarb vegetable. The manure adds organic value to the soil. The supplements of manure need to be 1/4 lbs. of phosphate 0-20-0 food per plant.

Best Fertilizers for Rhubarb

1. Southern Ag All Purpose Granular Fertilizer

Southern Ag in its 5 lbs. package has a homogenous granular formulation. All-purpose means that you can use for flower beds, roses, super large shrubs, trees, citrus family, and vegetables.

The NPK ratio is 10-10-10 which makes the fertilizer more balanced.

Here’s how to apply for each type. For vegetable gardens and flowerbeds, 1 cup per 25 square feet is enough. For roses and large shrubs, apply 2 – 2.5 cups per 4 feet of height. Lastly, for fruit trees, apply 2-4 cups per tree.

Be mindful to spread evenly in every area and then water the plant.

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2. Earth Organic 5 Fertilizer

Looking for a more tasty and healthy appearance of rhubarb and you want an organic fertilizer, yes Dr. Earth is 100% organic and has no GMOs, chicken manure, or sewage sludge.

The super beneficial pro-biotics and other natural ingredients (handcrafted by the way) are pet and people safe.

The NPK is a 4-6-3 ratio which means phosphorus is high in amount. If you remember I mentioned that during fall, rhubarb asks for more phosphorus than nitrogen, so that makes the fertilizer a perfect fit.

With the help of Dr. Earth, you can grow strong crops and healthy leaves, plus it fights pests. Yes, you will be free of pests since the smell is dreadful, there’s no way to send an invitation to the bacteria (theoretically).

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3. Scotts All Purpose Flower & Vegetable Plant Food

Scotts all-purpose fertilizer fixes all problems regarding feeding the plant. It’s great for use on all types of flowers and vegetables, besides the fertilizer feeds the plants for up to 2 months and specifically produces more flowers and fruits where you will end up with happy harvesting hours.

Scotts plant food is so easy to use and the brand claims that is safe to use. Also, it won’t burn your plants by any means if you follow the given instructions.

Using the NPK of 10-10-10 ratio, the fertilizer will help vigorous growth and nourishment of plants.

Here are the instructions on how to use it. 1 cup which is pretty much 9.5 oz. to cover 30 square feet, or apply 1/2 tablespoon of fertilizer for each 1 square foot area. Use the product every 2 months throughout the growing season starting from the spring. 

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Where is the Ideal Growth of Rhubarb?

If winter times are freezing in your area, this is the time to plant rhubarb in the garden. The plant needs chilling times at a temperature below 40 to produce stems. So, unlike the other plants, the coldest sections grow the best rhubarb especially in South zone 7. 

Why You can’t Leaves of Rhubarb?

Only leaves of rhubarb are inedible and they contain a high level of oxalic acid which is harmful to the human body. If you eat it, you gonna have to deal with stomachache, diarrhea, nausea, vomiting, or cramps. Don’t worry you won’t die, just suffer for a little while.

Why Mu Rhubarb is Dying and Failing to Produce?

The poor soil or drainage together with drought weather conditions drops the health of the rhubarb. Overfertilization can be another reason (fertilize twice a year) and overwatering which should happen once a week.

Why You Can’t Harvest Rhubarb in August?

Because you have harvested many times during the summer and that has weakened the roots. The harvesting needs to stop in the middle of July. Any harvest later won’t taste the same. 

A Brief Recap

Rhubarb with its bitterish and sweet taste garnishes our dish. So to feed you, first it needs to be fed. Apply fertilizer twice a year during spring and fall.

In the spring fertilization, look for heavy nitrogen ratio, and for fall fertilization, look for phosphorus concentration. Stop the harvesting in the middle of July and avoid eating the leaves as they are toxic.

Further Reading

I’m coming up with new assignments, check the related article about how and when you should fertilize azaleas

Additionally, find out what causes rosemary leaves to turn brown, and how to fix the yellow leaves of nasturtium

Stay tuned for the next informative articles.


Ella Holmes

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