Everything You Need to Know About Fertilizers
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WHEN TO FERTILIZE PLANTS
Soils should be supplemented with fertilizers every so often to replenish nutrients. The nutrients in soil slowly get used up as the plant grows. A good soil usually has enough nutrients to keep your plant happy for some good months. However, over time your plant can die. Months without fertilization can lead to a weak plant more susceptible to other diseases. You should apply them a couple months after repotting, and regularly during the growing season (usually spring/summer). Many plants (such as tropicals) should be fertilized year around, as they have no real dormant period. Use little to no fertilizer for plants during dormant periods.
FERTILIZER NUTRIENTS EXPLAINED
When shopping, somewhere on the packaging you will see three numbers (X-X-X). These three numbers are the % of Nitrogen – Phosphorous – Potassium in the fertilizer. N-P-K are the letter symbols for these elements on the periodic table. These are the primary nutrients that your plant absolutely needs to grow.
(N) Nitrogen – (P) Phosphorous – (K) Potassium
(N)Promotes leaf growth – (P)Promotes root growth – (K)Promotes flowering and fruiting and overall plant health and resilience
The secondary nutrients plants need are calcium, magnesium, and sulfur. There are many micronutrients that are needed in small doses as well. Beneficial bacteria are often added to organic fertilizers to help the plant absorb these nutrients.
SHOPPING FOR FERTILIZERS
There are two kinds of fertilizers you can buy; organic and chemical fertilizers. To start, I suggest buying a dry (sold in a bag) all-purpose organic fertilizer. See our Shop page for a larger selection of specialty fertilizers for different plants. I don’t recommend chemical ones for a variety of reasons explained in the table below.
I find that most plant shops in my area don’t have a wide selection, which is why I generally shop online. Manure based ones aren’t great since you don’t know what the animal was fed, and liquid organic types are watered down (although a fine option).
Great gardeners often talk about their soil more than anything else. Organic fertilizers enrich soil, and are packed with a large variety of nutrients, which make them superior than chemical fertilizers. Chemical fertilizers work quick and fast, but the trade-offs are not worth it. Chemical fertilizers are incredibly bad for the environment, and buying them is just supporting more destruction of rivers, lakes and oceans!
VISUAL SIGNS OF POOR FERTILIZATION
Results of not enough fertilizer:
- Slow growth
- Weak stems
- Bad resistance to disease and pests
- Flowers are small or poorly colored
- Pale leaves
Results of having too much fertilizer:
- White crust on clay pots and on the surface of the soil
- Malformed leaves
- Scorched looking leaf edges
Use fertilizers high in phosphorus when repotting.