How do you fertilize?

As summer arrives and the garden flourishes with growth, we are pleased to share valuable information on choosing the right garden fertilizer in this GARDENA Newsletter Special. We often hear the statement, "It came from my own garden; there's no fertilizer on that!" However, this proud claim of successfully grown fruits and vegetables is somewhat illogical. The truth is, for plants to thrive and produce valuable yields, they require an ample supply of nutrients. Each area of your garden, with its unique plants and purposes, needs to be fertilized appropriately to ensure optimal growth and development.

Is the fertilizer used irrelevant?

Each type of fertilizer, whether it is compost, manure, or corn fertilizer, has its own unique impact on the composition of the soil. Their different compositions also result in varied effects on plant growth. Furthermore, different plants have distinct nutritional requirements. For instance, rockery plants like sedum have different needs compared to shrubs like delphinium, and tomatoes have their own specific requirements as well.

While various plants have diverse nutritional demands, they all share the need for four main nutrients: nitrogen, magnesium, phosphorous, and potassium. Nitrogen is crucial for growth as it is a major component of proteins and an essential element in chlorophyll production. Magnesium is a key component of chlorophyll, contributing to photosynthesis. Phosphorous plays a vital role in promoting flowering, and potassium helps in strengthening plant tissues and facilitating fruit ripening.

The quantities of these nutrients required vary among different plant species. For detailed information on the nutrient requirements of specific plants, please refer to the fertilization tips provided below.

What about organic fertilizers?

The question of whether organic fertilizers are better than artificial fertilizers is not straightforward. It depends on various factors. From what we currently understand about plants, they do not differentiate between nutrients derived from organic or artificial fertilizers. Plants can only absorb nutrients in specific chemical forms that are available to their roots. The actual nutrients taken up by the plant are processed based on what the plant needs, rather than their origin.

The main advantage of organic fertilizers is typically their positive impact on the soil and the organisms that inhabit it. Over time, using only mineral fertilizers can degrade the soil in a garden because they do not provide the organic matter and nutrients necessary for soil health and biodiversity.

When using organic fertilizers, it's important to note that they take time to break down and release nutrients into the soil. Depending on the weather, it can take three to four weeks for organic fertilizers to fully dissipate and become available to plants. Therefore, if you want to provide nutrients to plants in April, organic fertilizers like horn meal or compost should be applied well in advance, in March.

Mineral fertilizers are particularly useful when you want to supply plants with nutrients quickly. There is also a middle ground between organic and artificial fertilizers, which includes mixed organic-mineral fertilizers that have an organic base with added minerals.

Regarding nutrient ratios in garden soils, phosphorous is often present in excess while nitrogen is frequently lacking. In such cases, using a compound fertilizer may not be the best approach. It is better to fertilize based on the specific needs of the soil. For instance, if the soil already has sufficient phosphate, it is advisable to use a nitrogen/potash fertilizer instead of a nitrogen/phosphorous/potash compound. Regular soil testing every couple of years can help determine the current nutrient levels and guide fertilizer application. This approach ensures better care for the soil in your garden and can even lead to cost savings by optimizing fertilizer usage. Additionally, it helps prevent excess fertilizer runoff, protecting valuable groundwater.

Now, let's move from theoretical knowledge to practical application. Let's take a walk through your garden together!

What needs to be fertilized now? And above all, how much fertilizer needs to be used?

For balcony and container plants, I prefer using a mineral-based potting mix. It retains the stored fertilizer well and doesn't get washed out with frequent watering. A high-quality flower soil usually comes with added fertilizer from the manufacturer, which typically lasts for about six weeks. At this point, it's necessary to replenish the fertilizer. During planting, I incorporate long-term fertilizer into the soil at a rate of 2-3 grams per liter of soil. This provides a basic food supply for the plants until around August or September. Additionally, I apply a small amount of liquid fertilizer every week when watering, usually 0.1 to 0.2 parts per thousand (equivalent to 10 to 20 ml of liquid feed for a full 10-liter watering can). Always follow the instructions provided on the fertilizer packaging.

In shrub gardens, the extent of fertilization depends mainly on the size of the plant mass formed by leaves and flowers. For rockery shrubs, I occasionally fertilize with a handful of horn meal or a small amount of compost (approximately one liter per square meter). Vigorous-growing bed shrubs can receive around 50 grams of compound fertilizer per square meter in spring (around March/April). Alternatively, three liters of compost per square meter can be applied. Weaker-growing shrubs only require 30 grams or 1.5 liters. In mid-June, a second application can be made with a slightly reduced amount.

In vegetable gardens, the fertilization approach varies based on the type of plant. Vegetables can be categorized as strong consumers (e.g., cabbage), medium consumers (e.g., tomatoes), and weak consumers (e.g., lettuce). Here are some specific fertilization recommendations:

Weak consumers: Apply 1 to 2 liters of compost per square meter and, if needed, additional nitrogen (approximately 70 grams of horn meal per square meter) and potassium (approximately 35 grams of potassium magnesium fertilizer per square meter).

Medium consumers: Apply 2 to 4 liters of compost per square meter and, if needed, additional nitrogen (approximately 120 grams of horn meal per square meter) and potassium (approximately 70 grams of potassium magnesium fertilizer per square meter).

Strong consumers: Apply 4 to 6 liters of compost per square meter and, if needed, additional nitrogen (approximately 150 grams of horn meal per square meter) and potassium (approximately 100 grams of potassium magnesium fertilizer per square meter).

Important note: Cabbages, onions, and carrots should not be planted in areas recently fertilized with manure. These plants should be introduced to such areas the following year to avoid potential intolerance. Some manure can attract flies, and their larvae may cause damage to the plants.

When fertilizing grass areas, it's important to consider the following points (as mentioned in the Lawn Special): Each time you mow the grass, nutrients are removed from the lawn. Approximately 30 grams of nitrogen, 20 grams of potassium, and 10 grams of phosphorous are lost for every kilogram of clippings that are removed. These nutrients need to be replenished. Decorative lawns generally require less fertilizer compared to lawns that endure foot traffic or stress. Typically, lawns are fertilized every four to five weeks starting from March/April, with a final autumn fertilization in early/mid-September to prepare for winter. However, there are variations now with the availability of long-term lawn fertilizers and specialized autumn fertilizers. It's crucial to carefully follow the instructions provided by the manufacturer on the lawn fertilizer packaging. This will also help in determining whether a general composite fertilizer can be used instead of a specific lawn fertilizer. Check the mix ratio of the composite fertilizer, specifically the nitrogen-phosphorous-potassium ratio. For lawns, the ideal ratio is 10:3:3-5.

When fertilizing trees, it's important to differentiate between deciduous trees and evergreens since their annual growth cycles and nutrient requirements differ.

Deciduous trees primarily require nutrients in early/mid-June and then again from mid-July to mid-August for a second growth spurt. Fertilization beyond this period is not recommended. Therefore, the first application of fertilizer for deciduous trees should be in April (approximately 55% of their annual requirement) and in June (45%). The ratios may vary slightly for fruit trees and roses, which may require a 50/50 or 60/40 split.

Evergreen trees require their first dose of nutrients in May and a second, higher dose between the end of July and the end of August when they are forming cones. The nutrient distribution for evergreens is therefore 35/65.

The amount of fertilizer required also depends on the plant's needs and the mass it forms. For small conifers, approximately 35 grams of composite fertilizer per square meter per year is sufficient. For the maintenance fertilization of trees and shrubs, around 50-70 grams of composite fertilizer per square meter per year should be adequate. Fruit trees, roses, and rhododendrons may benefit from the upper limit of 100 grams in both applications.

Keep in mind that the tree roots need to access the nutrients at the specified times. If you choose to use organic fertilizer, you need to consider the additional waiting period for decomposition when determining the application times mentioned above.

By the way:

Conservatory and indoor plants are now also in their growth phase - so do not forget to fertilize them regularly up to October. Use a green plant feed for green plants and a flowering plant feed for flowering plants - the latter contains more phosphorous to promote flowering.