For the plants to grow it takes fertilizer but which one?
Photo: Grøn Kommunikation
The garden needs fertilizer but it can be a jungle to find the right one. The most expensive, but in the long run most economical, and the most sustainable thing is to read what’s written on the bag. It needs to say “organic fertilizer” for you to be environmentally conscious.
When plants grow, they need fertilizer and even though the season for fertilizer traditionally starts in March or April, most people start now in May, which is no disaster. The biggest problem is to find the right fertilizer for the right place.
Soil and plants are different and need at times different fertilizer.
Moss in the grass
One sign of an unbalanced lawn is moss. The unbalance can be caused by the fertilizer proportion, the lighting conditions, high humidity or the like, that is the soil fits moss better than grass.
Moss is not easy to keep out of the garden. You can keep moss away on only wide plains.
Moss is in many ways a natural result of being too harsh on the lawn. The lawn is mowed often and consequently, it needs more nutrition. How much depends on the ground conditions. It is not enough to fertilize only in March, at least not if you use mineral fertilizer, often called lawn fertilizer or all-year fertilizer. None of these fertilizers is long-acting.
If you want to only fertilize once a year you need organic fertilizer, it slowly releases the nutrients which are then slowly dissolved. This means the grass will grow at a slow pace and is kept nice and green.
Most prefer NPK mineral fertilizer for the lawn, which is what the older gardeners call inorganic fertilizer. It is made from natural raw material but is quickly dissolved. One of the reasons why it is not very popular is that it cannot be controlled in the same way as organic fertilizer.
Often people use so much that when it rains it gets dissolved so fast that it is washed away and contaminates creeks. Also, mineral fertilizer does not better soil in the same way as compost or organic fertilizer. A soil which gets mineral fertilizer screams for more.
What does NPK stand for?
N stands for nitrogen, which is the nutrient used for growing all the green, so the lawn needs lots of that.
P stands for phosphor, which helps flower and fruit formation. The lawn does not need much of this.
K is the foundation of all plants. It stands for potassium and is crucial for the development of the root system. This is exactly what the lawn needs.
The NPK proportion is indicated on organic fertilizer. For lawns, it’s typically 8-1-9.
In mineral fertilizer, the proportion of NPK is 15-5-14
The numbers are the percentage of NPK. 15% N (nitrogen), 5% P (phosphor) and 14% K (potassium).
How often you need to fertilize depends on which fertilizer you use. Always read the instructions on the back of the bag. Typically, you fertilize in April, late June and August or September.
Expensive manure for the kitchen garden
In the kitchen garden, you can choose an organic and more expensive fertilizer if at least your garden is not filled with compost and manure.
Compost in itself contains very little fertilizer, but it is an excellent soil improver and it is good for the billions of microorganisms that fertilize the soil.
Fresh compost is too strong for the newly sown but good when the sown has grown a bit. Vegetables which have been fertilized too much with mineral fertilizer are in greater danger of pest infestation, than if fertilized with an organic fertilizer like manure.
Strawberries should not be fertilized before the berries sprout. If you fertilize too early, they will only get more leaves. Leek, cabbage and celeriac need very little but often.
Leguminous plants do not need nitrogen, they make it themselves.
If you choose all-year fertilizer NPK the rule of thumb is 1 pound per 1080 square feet of a kitchen garden.
Trees and hedges manage fine with all-year mineral fertilizer. You cannot count on the rule of thumb when dealing with trees and hedges but when you strew fertilizer in the garden, strew around the trees also and count the trees in the overall square feet.
Don’t strew the fertilizer close to the stem. The roots that need fertilizer are not close to the stem. That goes for roses too. Plants also need micronutrients which are found in both mineral and organic fertilizer and soil with added compost.
Acid soil beds are a whole other chapter. You can use all-year fertilizer or Nitophoska in the spring or choose an organic rhododendron fertilizer.
In a kitchen garden, you typically add 14-17 ounces of nitrogen (N) per 1080 square feet. The lawn is usually added with a maximum of 10.5 ounces at a time. The content of the different matters is indicated on the bag in the percentage of the weight.
Om Lars Lund
Danish horticulturist and journalist
Lars Lund has for many years engaged in the garden and greenhouse. Lars has published many books about greenhouses, and he has participated in many Danish horticultural TV shows. He is a walking garden encyclopaedia, and he has answers for most basic cultivation questions – also the more ambitious ones.