Fertilizing Routine for Indoor Houseplants
One of my most requested Houseplant post: what is my fertilizing routine? Note: this is not necessarily be the most optimal methods of fertilizing but it works great for me. Soil health and nutrients can get very complex, so take this as a jumping point.
Reading Fertilizer Labels
A super short and quick read on what the 0-0-0 numbers mean in this post.
Organic vs. Synthetic
For indoor plants, I use both organic and synthetic. I'm currently finishing up a bottle of Schultz synthetic and will switch 100% organic afterwards but there are merits to synthetics: they're cheap, odour-free, and allow nutrients to be readily available to the plant right away to boost quick results.
Tip: The only time I don't recommend synthetic fertilizers is in self-watering or no-drainage containers! That's because the fertilizer won't properly be flushed out of the soil regularly (through the drainage hole) and therefore can accumulate at the bottom of the pot/reservoir. The pooled liquid can gradually become potent with high levels of salts and can cause chemical leaf burn.
Every houseplant is different: the best thing to do is to look up the fertilizer preference of each of your houseplant. Some plants like rich soil, some like nutrient-poor soil that don't require fertilizing at all. This is my general purpose routine.
For my plants, since I mostly have tropicals, I use an all-purpose balanced fertilizer in the 10-10-10 range. I omit my cactus/succulents and carnivorous plants. For cactus/succulents I use Schult'z Cactus plant food, and for carnivorous plants I don't fertilize mine at all.
So here's my routine! It's super simple.
❶ Do Nothing:
If I've just repotted my plant with a commercial bagged potting mix, I don't actually fertilizer the first year. That's because they're usually created with enough nutrients within the soil to last for a while (usually compost, food pellets or some secret proprietary concoction). If I'm not mixing my own medium, I use Pro-mix.
This also applies to my newly bought plants; if the soil from the nursery is appropriate, it's adequate for me to leave for the first year.
❷ Worm Castings:
At the beginning of the next growing season after the initial potting mix has depleted somewhat, I'll add worm castings (following package direction) layered on top of the soil for each of my plant. This allows slow feeding throughout the months. I've used Jocelyn's Soil Booster and Gro4 Organics with success, but feel free to experiment with different brands.
❸ Schultz Plant Food:
For my plants that aren't fussy I'll use this synthetic Schultz liquid plant food. I apply it at half-strength and only really fertilize 3-4 weeks. I use this stuff pretty sparingly. One bottle will last you absolute ages.
❹ Earth Alive's Big Blue (Fish + Alga):
Together, these two organic amendments make for a gentle balanced feeding (Fish: 2-2-0 / Alga 0.3-0.3-4). It's recommend to use this weekly and foliar spray as needed. I use these even less frequently: once a month. This brand is hard to find online (I buy it locally), so another organic brand others swear by is Espoma.
❺ MARPHYL Soil Enhancer:
Update: 09/17/18: after finishing my Earth Alive fertilizers, I started using MARPHYL Soil Enhancer, a 100% natural and organic substance enriched in marine phytoplankton that adds nitrogen, phosphorus, potassium and minerals to the soil. I apply this every 1-2 weeks at a diluted 1:20 water ratio.
Word of Caution
My general attitude with fertilizing is that you don't need much at all (unless the plant is visible suffering from nutrient deficiencies). If you're using quality potting mix, use fertilizers sparingly. When in doubt, use half strength or less. My indoor plants flourish and grow at a steady rate because they're properly given their primary source of food: light. Fertilizing does not replace good light! Fertilizing goes hand-in-hand with light: proper light means the plant is growing, intaking nutrients and therefore will need replacing of said nutrients.
Fertilizing also does not guarantee your plants will grow quickly. Some plants are simply slow growers: look up the growth rate of your plant if you're in doubt, you'll likely find some relief.
Why don't you fertilize as recommended?
I dilute or fertilize infrequently because my home gets quite bright. The light actually "feeds" my plants well and they grow at a steady rate as is. I actually don't want them to grow too fast or else I'd run out of room! I fertilize mostly to keep the current soil well fed but I don't want to actually encourage larger growth. Your goal may be different!
All-purpose Fertilizer (Synthetic): Schultz
All-purpose Fertilizer (Organic): Espoma
Cactus Fertilizer (Synthetic): Schultz
Cactus Fertilizer (Organic): ESPOMA
Soil Enhancer (Organic): MARPHYL
Worm castings: Gro4 Organics / Jocelyn's Soil Booster