Because of its aroma, rhubarb is one of the most popular leafy vegetables to grow in your own garden. Points such as the large space requirement or the location must be considered for cultivation. One of the most important aspects of growing rhubarb is fertilizing and using the right fertilizer. Organic fertilizers are ideal for this purpose as they can be used for a long time and effectively.

5 suitable rhubarb fertilizers

Rheum rhabarbarumis one of the robust leafy vegetables that are cultivated in your own garden. The crop is healthy and vital, and thanks to the right care it is almost resistant to pests and diseases. Regular fertilizing before and during the growing season is essential for healthy rhubarb. Rhubarb is a heavy feeder that needs enough nutrients to develop the stems and leaves. Because of this, you need to use a fertilizer that will provide the necessary nutrients over a long period of time. The advantage: Organic fertilizers are ideal for strengthening the leafy vegetables. These slowly release the plant food to the crop. Mineral fertilizers, on the other hand, provide a nutrient boost that is quickly consumed.


Before you can apply the appropriate fertilizers, you must wait for the right time. Rhubarb does not necessarily have to be fertilized continuously, but some fertilizers allow more frequent use. The types of fertilizers used ensure a long-term supply of the site with the needed ones, which in turn stimulate the activity of microorganisms. These microorganisms have a positive effect on the vitality of the rhubarb plants. For this reason, fertilizer is used at two different times of the year:

  • March
  • after harvest

Fertilizing in March is important to support the plant in developing the stems and leaves, as these are the main uses. No further nutrients have to be administered until the last harvest time on St. John’s Day (June 24th). The plants get these all from the soil. After harvest, Rheum rhabarbarum needs to rest and needs another batch of fertilizer. From October there is no more fertilization, as from this point on the upper parts of the plant wither.


The classic organic fertilizer from your own garden is ideal for strengthening rhubarb. Make sure your manure is mature, fine, and of high quality. In this way, it can be easily incorporated, which makes your work easier in the long term. Since you need about three liters of compost per square meter, a well-seasoned one is particularly efficient. The compost is distributed on three dates:

  • when planting
  • in March
  • after harvest

When planting, the compost is thoroughly mixed with the potting soil and optionally bone shavings or flour. For the other two dates, fertilize by simply layering the compost. Compost is the all-rounder for your rhubarb.

horse manure

If you don’t have compost available, you can use horse manure to fertilize your rhubarb. Manure has some advantages over other fertilizers, especially in terms of nutrient content. Horse manure is extremely nutritious and only needs to be applied once before and after harvest. Horse manure is incorporated between January or March or placed directly on the soil around the plant. Since the manure has warming properties, you don’t have to worry about frost. Even the ice saints are only slightly harmful to the plants. The manure is used in the following ways:

  • apply a generous layer
  • distribute directly around the perennial
  • optionally incorporate into soil

More is not required for this variant. You can get horse manure from farmers or horse farms.

Tip: Classic horse manure or mount apples can also be replaced with a variety of other types of manure. Just be careful not to use cool manure such as goat manure as it will have less of an effect on the rhubarb.

nettle manure

Nettle manure is a good source of nitrogen after harvest, which supplies the weakened rhubarb until autumn. The biggest advantage of the liquid manure is the low acquisition costs, since you only need a rain barrel or a similar container made of plastic, ceramic or wood. In addition to the container, the following ingredients are required to make the nettle manure:

  • 1 kilogram of freshly harvested nettles
  • 10 liters of water

You should use rainwater or stale water from the hose as rhubarb doesn’t do well with hard water. The container is placed in a place that does not make it necessary to move the liquid manure. There is no need to find a shady spot as you will need to cover the bin. You can make the liquid manure in the following way:

  • Crush nettles
  • put in containers
  • pour into the filled container
  • stir well once
  • close with the lid
  • leave to ferment for two to three weeks
  • stir in between

While the liquid manure ferments for fertilization, an intense smell of ammonia and foam develop. The liquid manure is ready as soon as there is no more foam to be seen. If you find the smell too strong when stirring, add some rock flour to the broth. The flour binds the smell somewhat and makes the fermentation process more pleasant for the nose. Then dilute the liquid manure in a ratio of 1:10 with water and the organic fertilizer is ready. You can now fertilize your Rheum rhabarbarum some time after harvest. To do this, spray the liquid fertilizer directly onto the plant in the evening. This process is repeated every two to three weeks, depending on the vitality of the plants.

Tip: If you don’t have nettles available at the moment, you can use other plants to produce a nutrient-rich liquid manure. Field horsetail (bot. Equisetum arvense) and comfrey (bot. Symphytum) are recommended here.

horn meal or shavings

Horn meal and shavings are another form of fertilizer that you can use to fertilize your Rheum rhabarbarum specimens. However, this material is not a full fertilizer like compost or manure. The product is mainly used for strengthening and is given together with compost. For this reason, high amounts are not applied as they are used solely for site conditioning to provide the plants with sufficient nutrients as a slow release fertiliser. When choosing the fertilizer, you should pay attention to whether it is a young plant or an already established specimen that has had at least one winter:

  • Horn meal: releases nitrogen faster
  • Horn shavings: releases nitrogen more slowly

If you want to plant a completely new specimen, use horn meal to enrich the soil with the nutrients accordingly. The rhubarb plants can thus absorb the nitrogen after a short time, which has a positive effect on growth. This is not necessary for older plants, as the soil usually still has nutrients from last season. At the same time, the structure of the site would still have to be in good shape. Mix the shavings or flour, about 150 grams, into the compost and incorporate the mixture. After flowering you can also apply the fertilizer to strengthen your Rheum rhabarbarum.


If you don’t want to or can’t produce nettle manure, guano is a very good nitrogen fertilizer after the harvest. Guano is excrement from seabirds such as penguins or pelicans, as well as bats, which become a fine-grained mixture through limestone compounds. This contains sufficient nutrients, especially nitrogen, which makes it possible to fertilize your rhubarb plants. You can get guano in specialist shops. The mixture is applied in the following way:

  • Guano granules recommended
  • work into the top layer of soil
  • Dosage according to manufacturer’s instructions
  • pour on

In this case, you don’t have to do anything else. The granules are dissolved by the moisture and enrich the soil with important nutrients. Avoid using a guano spray solution, as the fertilizer can be quite caustic. In order to strengthen the rhubarb after harvesting, application at the location is recommended. Depending on the need, you can fertilize with guano at regular intervals until autumn. Above all, pay attention to how your specimens are doing and whether further fertilization is necessary.

Nutrient-rich protection against drying out

Rhubarb not only requires a large amount of nutrients, but water. For this reason, the crops are often covered with a layer of mulch, which protects the soil from drying out and at the same time provides an emergency food source. The mulch slowly releases more nutrients into the soil, which feed the leafy vegetables throughout the growing season. If you want to strengthen Rheum rhabarbarum with mulch, you can rely on the following types:

  • Grasschnitt
  • pine needles
  • compost from leaves

After you have placed the young plants in the bed or prepared the soil in the new year, you can spread the mulch layer. This method is very suitable if the location of the rhubarb dries out quickly or the location has problems retaining nutrients. You can solve this problem with mulching and support the growth of the rhubarb.

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