Chris's Development Blog

Growing Peppers with a Raspberry Pi

Background

So last year I attempted to create my first vegetable garden. I ended up getting cucumbers, peppers, and several different types of squash and planted them mid-summer. The cucumbers and squash are known as Cucurbits and are closely related, meaning that they all are very prone to the same kind of pests.

Anyways, because of the area I live in they were absolutely annihilated by every single type of pest that exists against them (this is not an exaggeration.) The only plants that produced anything were my pepper plants. So this year I decided to solely plant peppers and tomatoes to be safe.

I decided that I wanted to put about 36-40 plants in the ground this year so that a usable amount of vegetables were produced. In order to maximize the amount of peppers and tomatoes I would get I'd need to plant them before the beginning of spring indoors.

Early March I bought 5 varieties of pepper and 1 variety of tomato:

* Italian Pepperoncini Pepper
* Sugar Rush Peach Hot Pepper
* Leutschauer Paprika Pepper
* Jimmy Nardello Italian Pepper
* Pantano Romanesco Tomato
* Mammi Huber's Stuffing Pepper

Looking for the most cost effective way to grow a large amount of seedlings I landed on using a standard 1020 tray (these are trays that are 10x20in) and found some very cheap grow bags online which are normally used to start trees. I was able to fit 60 seedlings in a single tray and planted 8 of each pepper and 10 tomato seedlings, the rest of the spots I filled with basil and some melons from seeds I saved in the fall from cantaloupe and golden honeydew.

On the side I have another container made out of an old cardboard box with 20 spots that I filled with basil.

Problem

The basil sprouted in about a week, and the tomatoes followed closely behind, but after checking the peppers they hadn't even began to germinate and after doing some research I found out why they were taking so long. Peppers like it hot, very hot. The place I had the seedlings hovered at night around 60f to 70f during the day and in order to get peppers to germinate/sprout fast they need to be heated to around 85f.

Solution

Although a Raspberry Pi did not need to be used for this, I decided to regulate the temperature of the plants with a thermometer and heat mat. This was the sensor I decided to use, it uses a 1-wire interface and requires a 4.7k resistor between the data and voltage.

I also use a 5v 110v relay to enable or disable the heatmat. This is controlled by a GPIO pin on the raspberry pi.

This effectively adds a thermometer to the /dev/ directory which is pretty great because it can be used pretty easily in software.

A script I use to control the temperature ended up looking like this:

target_temp = 85
if temperature() < target_temp:
    state(true)
elif temperature() > target_temp:
    start(false)

I did notice that the temperature oscillates and never really quite hits the target, I think it is good enough for my application.

Overall, everything worked and within 5 days of using the heat mat the peppers finally emerged. I'm guessing they germinated before using the heat mat but were sped up by the heat. Everything else began to grow much faster with the heat as well. This was all very unscientific, however, and I cannot say for sure whether or not anything was changed by using a heat mat.

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