Rhubarb (Rheum rhabarbarum) is a perennial vegetable hardy enough for Minnesota gardens. It is in the buckwheat family, has a sour flavor and is among the first crops ready for harvest in spring.
Rhubarb is also a “pie-plant,” because you can cook, sweeten and use the chopped stalks as a pie filling, usually with strawberries.
You can also incorporate it into breads and cakes, sweet and use it as a sauce, or cook with sugar, strain and drink it as a refreshing juice.
Few people can eat much rhubarb as a raw vegetable. While juicy and crisp, it is very sour.
The Best Organic Fertilizer for Rhubarb – A Complete Guide
Rhubarb is a cold-hardy perennial that produces tasty stalks for use in pies, jams, and other recipes. While rhubarb is easy to grow, it does require extra nutrition to produce the best harvest. Using an organic fertilizer tailored to rhubarb’s needs is the key to success. In this comprehensive guide, we’ll cover everything you need to know about feeding rhubarb organically.
What Does Rhubarb Need Nutritionally?
Rhubarb has pretty high nutritional demands compared to other garden plants. It is a heavy feeder that rapidly depletes nitrogen reserves in the soil. Rhubarb also needs adequate levels of phosphorus and potassium for optimal growth. The ideal fertilizer for rhubarb has an NPK ratio around 10-10-10. This provides a balance of primary macronutrients. Secondary nutrients like calcium magnesium, and sulfur are also beneficial.
When Should I Fertilize My Rhubarb?
Timing is important when fertilizing rhubarb. The plant needs a good nutrient boost in early spring, just as the buds begin to swell. This ensures strong growth and stalk production. Another application can be made midseason if plants show signs of nutrient deficiency. Avoid fertilizing rhubarb in late summer or fall, as this can reduce winter hardiness.
How Frequently Should I Fertilize Rhubarb?
One heavy spring feeding is sufficient in most cases. However, rhubarb grown in sandy or nutritionally deficient soils may need a second application later in the growing season. As a general rule, established rhubarb plants should be fertilized once or twice per year. Newly planted rhubarb should not be fertilized for the first year after transplanting.
What is the Best Organic Fertilizer for Rhubarb?
There are lots of excellent organic fertilizer choices for rhubarb:
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Compost and composted manure provide a slow-release feeding of nitrogen, phosphorus, potassium and micronutrients.
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Fish emulsion is a fast-acting organic nitrogen source that gives plants a quick boost.
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Bone meal and rock phosphate are natural sources of phosphorus.
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Kelp meal adds potassium, micronutrients and beneficial compounds.
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Organic all-purpose fertilizers blended specifically for fruit and vegetables.
For best results, use a combination of fast- and slow-release organic fertilizers. This provides both an immediate nutrient infusion and longer-term feeding.
How Should I Apply Organic Fertilizer to Rhubarb?
Organic fertilizers can be applied in several ways:
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Spread granular fertilizer around the base of plants, being careful to avoid direct contact with foliage.
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Dig fertilizer into the soil around plants to a depth of 8-12 inches.
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Create a trench around plants and bury fertilizer 6 inches deep.
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Mix water-soluble fertilizers like fish emulsion into water and apply directly to soil.
Always follow label directions for correct application rates and methods. Water thoroughly after applying any fertilizer to move nutrients into the root zone.
Tips for Using Organic Fertilizers Effectively
Here are some useful tips for getting great results from organic fertilizers:
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Test your soil to identify any nutritional deficiencies before applying fertilizer.
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Combine fast-acting and slow-release fertilizers to get both quick and longer-term feeding.
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Rotate fertilizers annually to provide a wider spectrum of nutrients over time.
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Apply 1-2 pounds of 10-10-10 organic fertilizer per 100 square feet of rhubarb.
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Replenish the soil with compost or manure every 2-3 years.
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Side dress with extra nitrogen if growth seems weak midseason.
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Always follow label instructions carefully to avoid over-fertilization.
The Importance of Proper Soil pH for Rhubarb
Rhubarb does best in slightly acidic soil with a pH between 6.0-6.8. Adding lime raises pH, while sulfur can be used to lower pH. Test soil pH annually and adjust as needed. Proper pH ensures rhubarb can access nutrients from organic fertilizers.
Over-Fertilization of Rhubarb Must Be Avoided
It’s easy to overdo it with fertilizer, but this can damage rhubarb plants. Signs of over-fertilization include:
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Excessive leafy growth with fewer stalks.
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Burnt leaf tips or margins.
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Stunted roots and poor winter survival.
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Increased vulnerability to pests and diseases.
Go easy on fertilizer rates and always water it in thoroughly. It’s better to under-fertilize than overdo it.
Organic Rhubarb Fertilization Schedule
Here is a sample fertilization schedule for rhubarb using organic fertilizers:
Spring:
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Early spring – compost/manure + all-purpose organic fertilizer
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Mid spring – fish emulsion or fast-acting nitrogen
Summer:
- Side dress with compost/manure if plants are struggling
Fall:
- Late fall – apply rock phosphate or bone meal
By following this schedule, your rhubarb will get the steady nutrient feeding it needs for optimal stalk production. Adjust specifics based on your soil, climate and observed plant growth.
The Bottom Line
Providing balanced organic nutrition tailored to rhubarb’s needs is the secret to a plentiful harvest. Aim for an NPK ratio around 10-10-10 applied in early spring and summer. Combine fast-acting and slow-release organic fertilizers for the best results. With the right fertilization program, your rhubarb will produce bumper crops of tasty stalks year after year.
Soil pH and fertility
- The best soil for rhubarb is well-drained.
- Loamy soils are better for rhubarb growth than sandy soils. They are more water-retentive and can provide more nutrients to the plant.
- Soil pH is not important. Any garden soil in Minnesota, whether acidic, neutral or basic (“alkaline”), can support a good crop of rhubarb.
- Garden soil tests, because they are usually from parts of the garden with annual plantings, will not provide information about the rhubarb plants needs.
- The rhubarb plant is a “heavy feeder.” The plant must take in large amounts of nutrients from the soil to produce its large stalks and leaves.
- Make it an annual practice to supplement the soil with either a balanced commercial fertilizer or rich compost, or both. Addition of manure or compost can add micronutrients and organic matter to soil.
- Note whether growth is vigorous or weak, and adjust the next springs fertilizer application accordingly.
- Continuous use of high phosphorus fertilizer such as 10-10-10 or 15-30-15, or high rates of manure or manure compost results in phosphorus buildup in the soil.
- Some runoff may occur with phosphate fertilizer. It can then become a major pollution concern in our lakes, rivers and streams.
- High levels of phosphorus support over-production of algae, which causes significant reduction in water quality.
- If your soil tests high in phosphorus, use a low phosphorus (such as 32-3-10, 27-3-3, or 25-3-12) or no phosphorus (such as 30-0-10 or 24-0-15) fertilizer.
Gardeners often acquire rhubarb plants from another gardener who is dividing a large plant. Although there is a possibility of receiving a plant infected with a virus, chances are good that the plant is healthy and vigorous, since it is large enough to need dividing.
You can also purchase plants at garden centers and from mail-order catalogs. Nursery-grown plants will be virus-free.
Catalogs also sell rhubarb seed. The reddest varieties are not available as seed, only as plants.
- Different varieties have varying levels of sourness and fibrousness.
- Varieties also vary in color from almost pure green to almost pure red. Usually the skin is more or less red, while the flesh color varies from pale to darker green.
- Color does not cause any specific flavors. Redder varieties are desirable for pies, because the color of the filling is more attractive than the grayish color of cooked green varieties.
- Plant stature and vigor also vary among varieties. In general, greener varieties are more vigorous and have longer stalks than red varieties.
- Rhubarb leaves are toxic. Do not eat them.
- Only the long, thick leaf petioles, the “stalks,” are edible. The stalks contain high levels of oxalic acid, which can tie up calcium and make it unavailable in the body.
- Eating an occasional dish containing rhubarb does not pose a serious nutritional threat.
- People with gout, kidney disorders and rheumatoid arthritis may want to avoid foods high in oxalic acid and should consult with their physicians about consuming these foods.
How To Feed Rhubarb For Larger Yields!
FAQ
What is the best thing to feed rhubarb with?
Garden compost and well-rotted manure generally contain low levels of nitrogen, phosphates and potash (NPK).
How do you fertilize rhubarb naturally?
Manure is an extremely valuable source of organic matter, as it helps to conserve moisture, preserves the soil structure and makes nutrients readily available. If you choose to use it for your rhubarb, do not use fresh manure— this could burn the tender plants. Apply one to two shovels of older manure per plant.
Can you put Miracle-Gro on rhubarb?
Rhubarb is a “heavy feeder” which means it responds well to generous fertilizer, which can be granular 10-10-10 or a water-soluble type like Miracle Gro. That will help build energy for the plant.
What is the secret to growing rhubarb?
Rhubarb thrives in cool climates and requires a location that receives full sun or partial shade. Choose a spot in your garden that provides at least 6-8 hours of sunlight per day. Ensure that the area has well-drained soil, as rhubarb does not tolerate waterlogged conditions.