Knowing when and how to fertilize your houseplants can be a tricky topic but there are a few simple rules to follow that will keep your houseplants lush and healthy.
Rule 1 – know your plants
All plants are different and need different things. From light to soil to watering and feeding, the biggest killer of houseplants is being uninformed about your plants needs.
Rule 2 – know your fertilizer
There are also many different types and balances of fertilizer and making the right choice for your plants can make all the difference.
The first main distinction is organic vs. inorganic
Inorganic fertilizers are synthetic compounds made using only primary nutrients sourced from minerals and gasses. The main advantage to using this type is that the nutrients are already in their base forms and can be absorbed by the plants immediately. The disadvantages are that the nutrients are easily leeched away by quick draining water, and they lower the overall quality of the soil by introducing salts which can build up over time to fatal levels.
Organic fertilizers are sourced from organic material such as compost, guano or manure, bone and blood meal, fish meal or fish emulsions to name a few. The benefits to using organic fertilizers are more long term. They contain not only the macronutrients nitrogen, phosphorus, and potassium but are also rich in other nutrients like calcium, magnesium, sulfur, copper, iron, and zinc. In addition organic fertilizers actually improve the soil structure. The downside is that the nutrients have to be broken down into more basic forms before they can be absorbed by the plants.
Choosing the right nutrient balance
When you are shopping for a fertilizer there are three numbers that distinguish different balances from each other, but what do they mean?
The first number indicates the percentage of nitrogen (usually labeled N) present in the compound. Nitrogen promotes vegetative growth, which is green foliage. Plants that make up most of their mass in foliage like grasses, spider plants, and leafy vegetables like spinach or kale usually need a lot of nitrogen.
The second number is phosphorus usually labeled P. Phosphorus is mainly used by plants for root growth. Plants like carrots, turnips, and other root vegetables need lots of phosphorus. Most all young plants can benefit from an application of phosphorus but keep in mind that young plants can be quite fragile so be careful.
The third number is for potassium usually labeled K. Potassium helps keep plants healthy in general, it is the nutrient that is converted into sugars and starches. Potassium fertilizers are used to encourage flowering and to build the plants immune system and increase disease resistance.
There is one more factor to consider, the delivery method. Inorganic fertilizer comes in a few different forms.
Liquid feed is the most commonly used on indoor houseplants. This type is easily mixed to whatever strength is desired for any particular application and has the fastest results. The downside is that it is the most easily washed away. When using liquid feed we recommend using a half strength application two times during the growing season instead of one full strength application. This prevents most overfeeding problems and lengthens the time the nutrients are available. Before the second feeding of the year and before winter sets in we also recommend flushing the soil of salt deposits left in the soil by the fertilizer by overwatering a few times.
Time release fertilizers come in two types pellets, and spikes. Pellets are becoming more widely used than spikes because of the ability to more effectively control the amount and distribution in the pot.
Rule 3 – don’t use full strength applications
Recommended dosages on fertilizer packages are usually an overestimate, this is mostly a result of manufacturers desire to sell more product. A two thirds strength application should be sufficient with most brands or we recommend two half strength applications over the course of the growing season.