5 Best Fertilizers for Rhubarb | How and When to Use

With how easy rhubarb is to grow in most areas, there’s little excuse not to grow this generous vegetable crop in your own garden. (Unless that is, your growing space is limited. Rhubarb requires a lot of growing room, after all!)

Issues with rhubarb are pretty few and far between. It’s extremely hardy and resists a variety of pests. When gardeners do struggle to get the most from this plant, it usually comes down to not providing enough nitrogen or water during the growing season. That’s why following a simple, tailored fertilizer routine is the best solution to most rhubarb woes.

Best Fertilizers for Rhubarb

If you’re in a hurry today, here are my favorite fertilizers for growing big, thick rhubarb:

How to Choose the Best Fertilizer for Rhubarb

It’s easy to feel overwhelmed when learning how to feed and otherwise care for all of the plants in your garden. As far as rhubarb is concerned, however, a solid nitrogen-rich fertilizer will go a very long way. Unlike many commonly homegrown fruit and vegetables, rhubarb is less fussy when it comes to soil pH and micronutrients – although there are a few basic rules to follow, and I’ll explain what I mean by that below.

Rhubarb N-P-K Ratio Requirements

Nitrogen first and foremost, along with phosphorus, and potassium are the most important nutrients for rhubarb. These micronutrients are found in almost all fertilizers. And you can use something called an N-P-K ratio — a sequence of 3 numbers divided by hyphens — to easily determine the formulation of any given fertilizer.

For example, a basic 10-10-10 fertilizer contains 10% each of nitrogen, phosphorus, and potassium. Meanwhile, a 12-0-0 fertilizer contains 12% nitrogen and 0% phosphorus, and potassium.

Nutrient Requirements and Soil pH for Rhubarb

Rhubarb thrives in slightly acidic soil with a pH reading between 6.0 and 6.8. Most garden soil will fit within these parameters but it never hurts to test the soil before planting your rhubarb.

My main concern when growing rhubarb in neutral or alkaline soil is the risk of manganese deficiency. While the availability of other nutrients can also be affected by soil pH, this is the one you really want to watch out for.

Nitrogen Fertilizers

Since rhubarb is such a heavy feeder, it’s sometimes appropriate to apply pure nitrogen to the soil. This is best done in the spring before your rhubarb’s growth takes off for the season. I recommend reaching for pure nitrogen fertilizer when the soil contains adequate amounts of other nutrients.

Using Bonemeal to Fertilize Rhubarb

Bone meal is an organic source of phosphorus that works quite well on rhubarb. It can be used to address phosphorus deficiencies or to prep the soil prior to planting new rhubarb.

Granular Vs Liquid Fertilizer

When it comes to rhubarb, I prefer granular fertilizers over liquid ones. Granules release nutrients into the soil more slowly which ensures your rhubarb stays well-fed throughout the entire season.

Liquid fertilizers are extremely useful for addressing urgent nutrient needs. I recommend using liquid fertilizers to jump-start your rhubarb in early spring. You can also use it to supplement the soil with micronutrients – if needed – throughout the year.

Synthetic Vs Organic Fertilizers for Rhubarb

To be clear, both synthetic and organic fertilizers are excellent sources of nutrition for rhubarb. If your main concern is providing valuable macro- and micronutrients, then I think the choice between synthetic versus organic formulas is largely a personal one.

With that said, many organic fertilizers benefit the soil by adding more than just basic nutrients. Materials like aged compost and manure, in particular, can improve overall soil quality while simultaneously providing the nutrients your rhubarb needs to thrive.

Best Fertilizer for Rhubarb Reviews

Feeding rhubarb involves more than just choosing the right formula. But that doesn’t mean just any fertilizer will do. In my opinion, these formulas offer the ideal balance of nitrogen while also supporting overall soil health and productivity throughout the years.

Pros

• Ideal for spring feedings
• Various application methods

Cons

• Low in phosphorus

Miracle-Gro is an extremely popular brand that you can easily find in your local garden store or order online. If you’re interested in liquid fertilizer, I recommend this water-soluble formula from the brand’s Performance Organics line.

This fertilizer is perfect for heavy-feeding rhubarb along with many other edible fruit and vegetable plants such as cabbage and broccoli. Since feeding can be incorporated into your watering schedule and can be repeated weekly. Add the required amount to either your watering can or hose attachment and away you go!

This is a great option for use all season long. Use as a springtime feed since it’s high in nitrogen which means stems and foliage production will get off to a flying start. They, continue using this all season long since it also contains the phosphorus required to support root growth as well as potassium.

How To Use: For small areas, dilute fertilizer in a watering can before applying it around your rhubarb plants. For larger areas, add fertilizer to a compatible hose attachment and apply.

Pros

• Excellent source of nitrogen
• Promotes growth early in the season
• Adds organic matter to the soil

Cons

• ‘Organic’ smell

For a burst of nitrogen at the start of the growing season, few fertilizers are as effective as Down to Earth Blood Meal. It’s one of my favorite ways to deliver pure nitrogen to the soil.

The slow-release granules in this organic high-nitrogen fertilizer can be used as a top dressing or base dressing for rhubarb as well as the other heavy feeders in your vegetable bed. 

I recommend using this blood meal supplement on soil that is already full of phosphorus, potassium, and other nutrients. Alternatively, you can combine it with your preferred source of phosphorus for balance.

One other thing to consider when using this feed is its attractiveness to animals! It contains odorous animal matter such as blood meal, bone meal, and fish meal which is of great value to plants but can pose the risk of inviting deer and other animals to your plot.

How To Use: Apply 1.5 lbs per 50 square feet and apply as a top dressing. Work blood meal into the soil around rhubarb plants and water thoroughly.

Pros

• Certified organic and non-GMO
• Adds probiotic microbes to the soil
• Can be used to make compost tea

Cons

• It May have an odor

This Dr. Earth slow-release fertilizer offers a nice balance of macronutrients that can be used all year round, but in particular, is my go-to when preparing rhubarb for the fall and winter. That’s because the 6% phosphorus ratio encourages roots to continue to grow and will protect plants against freezing temperatures. 

In spring, I like to combine this with an organic fertilizer like aged compost or manure. This strategy ensures my rhubarb has access to plenty of nitrogen during the peak growing season. Then, as the season progresses to more clement weather, I use this fertilizer and there is no need to supplement with anything else.

How To Use: Spread granules around rhubarb plants, being careful not to touch the leaves or stem. Water the soil immediately to activate the fertilizer.

Pros

• Great for spring and fall applications
• Good source of phosphorus
• Contains beneficial bacteria and fungi

Cons

• It May have a bad odor

Another great phosphorus-rich fertilizer is this one from Jobe’s Organics. It’s a slow-release formula that also contains beneficial soil microbes.

This is a wonderful fertilizer to have on hand for rhubarb because it is quite versatile. I like to use it at the end of the growing season to prepare plants for overwintering. But it also pairs nicely with a nitrogen source like a blood meal for spring feedings.

How To Use: Spread fertilizer around the base of your rhubarb plant underneath the leaves. Water immediately after applying.

Pros

• Listed for organic production by OMRI
• Natural source of nitrogen
• Easy to spread

Cons

• Not a complete fertilizer

While there are many kinds of blood meals available to home gardeners, I want to highlight just one more that I think stands above the rest. This Burpee blood meal is an excellent source of nitrogen for rhubarb plants. It’s certified organic and has a very nice, easy-to-spread consistency compared to some other formulas. 

I recommend adding this soil amendment in the spring. Pair it with other nutrient sources as needed.

How To Use: Work the fertilizer into the soil beneath your rhubarb’s foliage. Water thoroughly after applying.

How to Fertilize Rhubarb

If your rhubarb is planted in high-quality soil, you may not need to apply a complete fertilizer every year. However, nitrogen is almost always needed in the springtime to support annual growth.

I recommend sourcing nitrogen from compost, manure, or a similar material whenever possible. Rhubarb benefits greatly from the organic matter these natural fertilizers add to the soil.

New Plantings

Do not fertilize rhubarb for at least a year after planting. There’s a very good chance fertilizer will damage or even kill young plants and it’s not worth the risk. The soil can be lightly amended with aged compost or manure if needed. But I suggest doing this prior to transplanting your rhubarb.

Fertilizing Established Rhubarb

One established, rhubarb consumes a large amount of nitrogen each growing season. It’s important to replenish this nitrogen lest your rhubarb plants start to lag behind previous years’ harvests.

Avoiding Fertilizer Burn

To prevent fertilizer burn caused by too much nitrogen, be sure to measure all fertilizer applications and supply rhubarb with plenty of water. Since rhubarb is a heavy feeder, however, this type of fertilizer burn is fairly uncommon.

Rhubarb more often falls victim to fertilizer burn caused by granules making contact with the foliage. Always apply fertilizer — with the exception of foliar sprays — directly to the soil. Immediately wash away any fertilizer that does touch the plant itself.

When to Fertilize Rhubarb

At a minimum, rhubarb should be fed with a rich nitrogen source in early spring. Apply a nitrogen-rich fertilizer just before annual growth starts to get the most out of your rhubarb patch. Particularly vigorous plants may benefit from a second application of nitrogen in the summer. For the best results, I also recommend applying a high-phosphorus fertilizer in the fall.

How Often to Fertilize 

I recommend fertilizing rhubarb with a slow-release granular formula up to 3 times per year between early spring and fall. If you opt to feed with liquid fertilizer or foliar spray as well, check the label for the best application frequency.

Verdict: Best Fertilizer for Rhubarb

Rhubarb is a hardy vegetable that tends to fly under the radar when it comes to seasonal maintenance. But proper nutrition is often the secret to growing the largest and most flavorful rhubarb around.

In the spring, I prefer to use an organic fertilizer like aged compost or manure for the bulk of my rhubarb’s nutrition. If your rhubarb needs an extra dose of nitrogen, add Down to Earth Blood Meal Fertilizer Mix 12-0-0 to the soil as well. As the season progresses, a liquid formula like Miracle-Gro Performance Organics All Purpose Plant Nutrition 11-3-8 can be used to keep nutrient levels high.

You may also be interested in reading The Best Companion Plants for Rhubarb | Good and The Bad

FAQs Fertilizing Rhubarb

How do I grow thick rhubarb stalks?

Rhubarb stalks grow thick when all of their needs are met. The best thing you can do to encourage thick growth is to stick to a recommended fertilizer and watering routine. If your rhubarb plant is fairly young, give it a couple of years to mature before evaluating its thickness.