When To Fertilize Rhubarb

Knowing when to fertilize rhubarb is the key to strong, healthy plants that produce thick, flavorful stalks for years. If you get the timing wrong, you might end up with lots of leaves and little to harvest. This guide gives you the simple schedule and methods for optimal growth.

Rhubarb is a hardy perennial, but it’s also a heavy feeder. It uses up a lot of nutrients from the soil to support its large leaves and thick stalks. Feeding it at the right times supports vigorous growth and a long harvest season. Let’s look at the best times to feed your plants.

The main feeding times for rhubarb are early spring and again after the harvest ends. A third, optional feeding can happen in late fall. This schedule matches the plant’s natural growth cycles, giving it fuel when it needs it most.

1. Early Spring Feeding (The Growth Starter)

This is the most important fertilization of the year. Apply fertilizer as soon as you see the first tiny pink knobs (called “buds” or “eyes”) peeking through the soil. This usually happens in late March to early April, depending on your climate.

Why now? The plant is waking up and preparing for a major growth spurt. A nutrient boost at this stage helps it produce those classic large leaves and thick, juicy stalks. It sets the stage for your entire harvest.

Best for this feeding: A balanced, all-purpose fertilizer (like a 10-10-10) or a generous helping of well-rotted compost or aged manure.
Key Tip: Keep fertilizer off the emerging buds to prevent burn. Apply it in a ring around the plant, not directly on the crown.

2. Post-Harvest Feeding (The Replenisher)

Stop harvesting rhubarb by mid-summer to allow the plant to recover. Right after you take your last stalks, it’s time for the second feeding. This is crucial.

Harvesting takes a lot out of the plant. This fall feeding helps it rebuild its energy reserves, which are stored in the roots for next spring. It’s like giving it a good meal after hard work.

Best for this feeding: Compost or a fertilizer with less nitrogen and more phosphorus/potassium to encourage root and crown health.
Key Tip: Water the fertilizer in well to help the nutrients reach the root zone.

3. Late Fall Feeding (The Optional Prep)

After the first hard frost, when the leaves have died back, you can add a thin top-dressing of compost or well-rotted manure. Don’t use chemical fertilizer now.

This isn’t for immediate feeding. The material will sit over winter, slowly breaking down and enriching the soil for spring. It also acts as a mild mulch. This step is extra beneficial for older, established clumps.

What Happens If You Fertilize at the Wrong Time?

Timing mistakes can hurt your plant. Fertilizing too late in summer or early fall with a high-nitrogen fertilizer can stimulate tender new growth that will be killed by frost, wasting the plant’s energy. Under-fertilizing leads to weak, spindly stalks and smaller leaves.

Signs Your Rhubarb Needs Food

Stalks are thin and stringy, not thick and crisp.
Leaf size is significantly smaller than in previous years.
The overall plant looks weak and isn’t producing many stalks.
The color of the stalks might be less vibrant.

Choosing the Right Fertilizer for Rhubarb

You have two excellent paths: organic amendments or commercial fertilizers. Both work well when applied correctly.

Organic Options

These improve soil structure as well as feed the plant. They are gentle and release nutrients slowly.

Well-Rotted Manure: Cow, horse, or chicken manure that has aged for at least 6 months is fantastic. Fresh manure can burn plants and introduce weeds.
Compost: Your own garden compost or purchased compost is perfect for all three feeding times. It’s hard to overdo it with compost.
Other Amendments: Blood meal (for nitrogen), bone meal (for phosphorus), and seaweed emulsion are also good choices.

Commercial Fertilizers

These provide a quick, measured nutrient boost. Look at the three numbers on the bag (N-P-K).

For Spring: A balanced formula like 10-10-10 is ideal.
For Post-Harvest: A formula lower in nitrogen and higher in the last two numbers, like 5-10-10, supports root recovery.
Always follow the application rates on the package. More is not better and can harm the plant and soil life.

Step-by-Step Guide to Fertilizing

Here is the simple process to follow for each feeding.

Clear the Area: Gently remove any weeds or debris from around the base of the rhubarb plant.
Apply Fertilizer: For granular fertilizer, sprinkle it in a ring about 6-12 inches from the crown. For compost or manure, spread a 1-2 inch layer over the soil in the same area.
Water Deeply: This is essential! Water the area thoroughly to help dissolve granular fertilizer and wash nutrients into the soil. It also prevents root burn.
Optional Mulch: After feeding in spring or fall, you can add a layer of straw or shredded leaves to retain moisture and suppress weeds.

Special Feeding Notes for Young vs. Established Plants

A new rhubarb plant and an old clump have different needs.

Newly Planted Rhubarb (First Year)

Do not harvest any stalks in the first year. Let the plant establish itself. Focus on feeding the soil at planting time with plenty of compost mixed into the hole. A light feeding in early spring of its second year is fine, but the main focus should be on consistent watering and soil health.

Established Rhubarb (3+ Years Old)

These are the heavy feeders. They have likely exhausted the original nutrients in their spot. Stick to the main two- or three-feeding schedule religously. Established clumps often benefit from being divided every 5-8 years, which is a perfect time to refresh the soil with compost in the new planting holes.

Common Mistakes to Avoid

Fertilizing in Late Summer: As mentioned, this spurs new growth vulnerable to frost.
Using Fresh Manure: It can “burn” plants due to high ammonia and salt levels.
Placing Fertilizer on the Crown: This can cause rot and damage new buds.
Over-fertilizing with Nitrogen: Leads to enormous leaves but disappointingly thin stalks.
Forgetting to Water it In: Granular fertilizer left on the surface won’t help the plant and can form a crust.

FAQ: Your Rhubarb Fertilization Questions Answered

Can I use tomato fertilizer on rhubarb?

Yes, you can. Tomato fertilizer is often higher in phosphorus and potassium, which is actually suitable for the post-harvest feeding to encourage root and crown strength. For spring, a balanced fertilizer is still prefered.

Is Epsom salt good for rhubarb plants?

Epsom salt provides magnesium and sulfur. If your soil is deficient in magnesium (shown by yellowing between leaf veins), a light application can help. But it’s not a complete fertilizer and shouldn’t replace your main feeding schedule.

How often should you fertilize rhubarb?

Stick to the core schedule: once in early spring and once after harvest. That’s twice a year. A third, light fall feeding with compost is optional but beneficial. Over-fertilizing is a common problem.

What is the best natural fertilizer for rhubarb?

A combination of well-rotted manure and garden compost is hard to beat. It feeds the plant and builds healthy, living soil full of beneficial microbes that support optimal growth for the long term.

Should you fertilize rhubarb in the fall?

You can add compost or aged manure as a top-dressing after frost. Avoid any strong chemical fertilizers in the fall, as the goal is to enrich the soil for spring, not stimulate immediate growth.

Getting the timing right for when to fertilize rhubarb makes all the difference. By following the simple spring and post-harvest schedule, you give you’re plants exactly what they need when they need it. Remember to choose your fertilizer wisely, apply it carefully around the plant, and always water it in well. With this care, your rhubarb patch will reward you with abundant harvests for many seasons to come. A little attention to feeding goes a long way with this reliable garden perennial.