Why Do Plants Need Fertilizer? We have always been taught that plants need a few basic things to survive: Sunlight, Water, Air and Soil. Sunlight is the plant’s food. They use the energy from the sun’s rays to take air (CO2) and water to make sugar, which they then burn for energy. So if light, water and air are used to feed the plant, what does it need the soil for? The soil has 2 main roles to play; first it acts like a sponge to hold water for the plant’s roots to absorb. Second, the soil is often full of nutrients such as Nitrogen, Phosphorous and Potassium, which are essential for strong and healthy growth. These nutrients are necessary for the plant in the same way that we humans need certain vitamins and minerals. Without Light, water, and air, a plant will starve pretty quickly, which is why most plant care instructions pay special attention to each plant’s unique light and water requirements. Without the proper nutrients, a plant can live but it may not thrive and can be left susceptible to attack from pests.
Common signs that your plant is in need of fertilizer: When there are sharp differences between the older leaves and the newer leaves, your plant is most likely missing some key nutrients. Nutrient deficiency can affect the color, size and shape of leaves. It is usually most noticeable if:
-Fully developed new leaves are smaller than fully developed older leaves.
-Either all the old leaves are turning yellow or all the new leaves are.
-The new leaves are a pale green, and stay pale green when fully developed (Many plants will have lighter green leaves as they are growing, but once fully developed they will darken. If they stay pale green and never darken this could indicate a nutrient deficiency that is preventing the leaf from making enough chlorophyll.
-ALL the new leaves have an odd shape or texture that varies greatly from the older leaves. If only one or two new leaves are misshapen or odd textured that is usually due to some sort of physical damage that occurred as the leaf/leaves were developing.
Besides differences between old and new leaves, a sudden pest infestation that crops up with no known origin can often indicate nutrient deficiency. We’ll talk about pests and how to tackle them in a future post, but we often will start treating an infested plant by fertilizing it.
There are a few things to look for when buying fertilizer. Most all purpose fertilizers will work for your standard houseplants. These fertilizers usually have approximately even ratios of Nitrogen : Phosphorous : Potassium (NPK). These are the nutrients that plants need in higher concentrations, other nutrients such as calcium, magnesium, sodium and sulphur are equally important but needed in much lower concentrations. Whatever fertilizer you choose should contain all these elements and you should follow the instructions on the package for how to introduce them to your plant. In our shop we sell and use Maxsea All Purpose fertilizer as we have had the best results with it and it can be used in different concentrations for all the various plants we sell from tropicals to succulents to air plants, orchids and even carnivorous plants. For your standard tropical houseplants you can generally fertilize your plants every two weeks during the growing season. It is good to do a thorough watering in between fertilizer applications to rinse out any excess fertilizer before adding more.
Carnivorous plants: Most carnivorous plants don’t need fertilizer as they get their nutrients from the insects they trap. Some types of carnivorous plants can grow faster with very light and infrequent fertilization; often this leads to lots of healthy leaves but less impressive traps. If you choose to fertilize, use 1/10th the recommended amount of Maxsea. It is important to not fertilize the soil for these plants but instead to apply the fertilizer to their traps. For pitcher plants add it directly into the pitcher, for sticky plants lightly mist the sticky traps.
Cacti and Succulents: These plants generally do not need as much fertilizer as standard tropical house plants. During the growing season they will be happy with half the recommended concentration of Maxsea applied once a month. They don’t need any fertilizer in the winter months.
Tillandsia (Airplants): You can add your fertilizer directly to the water you soak your plants in every other time you water them during the growing season. If using all purpose Maxsea you should use a 1/10th dilution of the recommended amount. We have also had success with the fertilizer Epiphytes Delight which you can use as directed.
Orchids (most readily available species): Use ½ the recommended amount of Maxsea every third time you water during the growing season. Do not fertilize in the winter months. It is especially important to rinse the soil to remove excess fertilizer before adding more.