How to Feed Hydroponic Bok Choy
Look at these things! I think my Bok Choy might be on steroids. They’re growing so fast that I can barely keep up. In order to head off nutritional problems before they start, I have devised a “touch” test in order to determine when it’s time to give them more nutrients, which I will describe in this post.
At then end of this post I have also included recommendations for an E.C. nutrient increase schedule, recommended nutritional ratios, and pH level.
These Bok Choy are Out of Control!
Just 8 days ago they looked like this…
2 days ago, they looked like this…
Is it me, or did these Bok Choy get even bigger between now and Saturday?
These Bok Choy are Shanghai Green Choy. They are the most successful plant that I have grown to date. In the past 10 days their growth rate has increased massively.
Shanghai Green Choy Nutritional Needs
This is a small variety of Bok Choy. They will grow to be 8 inches tall. Today, they are 3–4 inches tall. Most sources say that Shanghai Green Choy take 50 days to grow to maturity, not including germination time. Mine probably have 18 days to go.
You can see that they have thick stems and thick and bushy leaves that have strong veins. They are big in comparison to say, Arugula, which is more delicate and grasslike. These plants need a higher level of nutrition than Arugula.
It’s been difficult however, for me to keep up with their needs. Just a week ago they were pretty small (see the photos at the top of the blog post) and about three weeks ago they were literally seedlings, just graduating from their germination trays to the big buckets!
The “Touch” Test: How to Detect Nutritional Deficiency Before It Stunts Your Plants’ Growth
The nutritional requirements of my Bok Choy seem to grow in a non-linear fashion. Increasing their nutrients during their once-a-week water change was not enough. I had to improvise a little bit in order to figure out the right nutrient schedule for them.
In order to keep up, I devised a “touch” test, which I use along with some other indicators, in order to help me determine when it’s time to increase their nutrients.
Brush your hand across the leaves and feel for “floppiness”. When you find a floppy leaf, it will be obvious. The floppy leaves will have one or more of the following characteristics:
- they will be paler than healthy leaves
- they will probably feel unusually soft
- they won’t resist the pull of gravity that well and they will tend to curve downward
- they may be relatively “featureless”. They will tend to be flat, like they haven’t developed properly
The next thing to do is to verify that nothing else is affecting your plants’ abilities to absorb nutrients like incorrect pH, and also that your water levels are high enough, i.e. your plant isn’t simply “drying out” due to lack of water.
Why do “Floppy” Leaves Mean that My Plants Might Need More Nutrients?
Floppy, soft leaves indicate that your plant can’t hold onto water very well. Your plant is technically “wilting”.
Nutrient salts inside of your plant attract water. Your plant retains more water when it has higher levels of nutrient salts running through it. It’s a lot like how high sodium foods make the human body retain more water.
As plants grow, their leaves get larger and their requirement for water is higher. Big plant leaves however, won’t retain enough water if they don’t have enough nutrients to help them hold onto that water. The water will evaporate out of the plant more easily in this case. Lower water levels in a plant leaf, means that the intra-cellular pressure will be lower, and the plant leaf will tend to “flop”.
The nutrients are also important for development, which is why we don’t just check for softness and floppiness, but we also check for lack of features in the leaves.
Recommended N-P-K and Nutrition Schedule for Shanghai Green Choy
I recommend an NPK ratio of 2–1–3 for this kind of Bok Choy. Here is a really easy to use and really affordable 2–1–3 ratio feed by General Hydroponics.
I personally like the 3 part system by General Hydroponics, because it controls pH balance better. It however, requires more calculation and is harder to use. I will do a post later about how to calculate the ratio of nutrient solutions properly in order to achieve a certain NPK ratio.
Also, keep the pH between 6.0 and 6.5. I use the General Hydroponics pH Up and Down solutions for this.
The Nutrient Increase Schedule
This schedule is exactly what I have done for my Shanghai Green Choy up till now and what I believe the schedule will look like for the next 2 weeks of their growth. You should still use the touch test to help you determine “how you’re doing”. This is because lots of things affect the growth rate of your plants like light level, heat, cold, water level, bacteria, algae, or (shudder) bug infestations.
All nutrient measurements are in millisiemens/cm, which is a measurement of E.C. (electrical conductivity). This is the Apera meter that I use to measure E.C. and pH, which also measures ppm and tds.
day 0: 0
day 5: 0.35
day 10: 0.6
day 14: 0.8
day 30: 0.9
day 34: 1.0
day 36: 1.1
day 39: 1.2
day: 46: 1.35
day 53: 1.35
UPDATE
I just harvested a couple Bok Choy.
They’re 7–8 inches tall with large leaves that are a little bigger than my palm. Their stems grew up to be strong and crunchy. I turned these ones into a stir fry. They were big enough that I only used two for two people.
The Shanghai Green Choy were really easy to grow. They were harvestable as baby Bok Choy after 39 days. The above pictures are of 56 day old Bok Choy.
