Determine what to Automate

To start off, let’s break down automation into some logical groups of systems by function:

  • Watering
  • Sunlight & Grow Lights
  • Nutrient Replenishment
  • PH Level Regulation

Each of these four groups can be implemented in phases if you so choose.


Watering is probably a good first phase choice to automate. Watering needs must be tended to more so than PH level regulation or nutrient replenishment. If your trees have ample natural sunlight while indoors, your yearly care taking time required will go down astronomically with a self watering system in place. Once calibrated and programmed well enough, you can much more easily identify problems with your trees since overwatering and underwatering can be ruled out as causes.

Sunlight & Grow Lights

Citrus trees require at minimum six hours of sunlight a day. Ideally, there should be eight or more hours of direct sunlight each day. While housed indoors, you may find that your trees aren’t getting enough sunlight. Not to worry! Purchase a full-spectrum grow light online or at a local retail store. There are many options available with varying sized fixtures, bulb types(florescent or LED), number of lumens produced, and home placement options(hooks for hanging from ceiling or integrated as part of a shelving unit).

Do your homework!

Florescent light bulbs burn out much more quickly than LEDs, more easily heat, and have higher kilowatts per hour (KPH).

Do have one or two plants or a small forest like me? Do you plan on buying more trees in the future? If so, the cost of buying a larger grow light with more bulbs and artificial sunlight may be cheaper than having multiples ones that produce an equivalent amount of light.

Do you intend to store your citrus plants in one central location or will they be multiple spots around your home? The answer to this question will aid in determining how many lights and their size you should purchase.

Keep in mind, no matter what anyone else tells you, there is no artificial replacement for actual sunlight.

Nutrient Replenishment

There are couple different strategies for nutrient replenishment you can employ with varying degrees of automation. You may be asking yourself, “if nutrient deficiencies are mostly spotted via the visual observation of the leaves, how can our microcontroller figure it out?”. Great question! We fundamentally need to make assumptions if you are feeding via your automated nutrient replenishment system.

Strategy 1: Semi-Automated: LED Light Indicators guessing soil deficiency

For most people, feeding isn’t a strenuous activity to do by hand. People just need to know when fertilizer should be applied and which kind. Using LED lights to represent the Arduino’s best guess at nutrient deficiency. Take a look at the leaves. If you agree with your Arduino, use the right fertilizer for the deficiency. If you disagree, no harm done.

I recommend this strategy for must people. It leaves total control in your hands.

Strategy 2: Automation with Assumptions; Human-triggered Specific-feeding

This strategy is for the most adventurous type of citrus enthusiast. You’ll need to be tech-savvy with a willingness to go through trials and tribulations of experimentation.

By human-triggered specific-feeding I mean that the citrus grower will be able trigger a specific type of feeding from a menu of options to each individual tree. Simply said, you choose the plant and tell it what it gets feed.

PH Level Regulation

Nutrient replenishment and PH level regulation are interdependent systems. There can be issues when you introduce too many nutrients to the soil, making the PH level rise.  There is no universal rule across all citrus species on the appropriate PH level for citrus growth and fruiting. There is variation between different types of citrus.  Research what the ideal PH level is for ideal for each species of citrus you own. Maybe put on the container the plant is in so you don’t need to look it up again when you program your Arduino or other device.

In reality, citrus trees aren’t some stupid plant that can’t manage to adapt to changes in environment including soil composition and nutrient balance. In other words, you don’t have to be spot on the money accurate. You can have a having producing orange tree at a PH level of 6 or a PH level of 8.  How precise you want to be is up to you.  Generally speaking, a PH range in-between 6.5 and 7.5 is preferable.

You can choose to program your microcontroller using this rule of thumb range or you assign each plant its own range giving you total control. When programming down the individual level you add another layer of complexity dealing with being able to change the PH Level ratio “on the fly”.

One solution to this problem is to start with the highest PH level plant and work down to the lowest PH level tree. In this way, you can apply more soil acidifer as the PH Level decreases without the need to add something else to increase it after potentially the beginning of the batch.

Another solution is to calculate the ratio of water vs soil acidifer content given the volume of water used for one duty cycle of a plant. This ratio tells you how much soil acidifer you would need to mix into the water used for watering to alter the PH level to the desired range for this specific plant. Initially, you would read what the PH sensor from the pot to figure out how much the level needs to decrease.

Both solutions together create a streamlined and efficient process that’s completely automated except needing to replenish your soil acidifier supply periodically.