DIY Temperature and Humidity Monitor for the Garden

This week I’m building a temperature and humidity monitor to take measurements in the Cold Frame I placed outdoors.  This is mainly for my own curiosity and will help assess how well the Cold Frame is at maintaining stable temperature and humidity.  I will also be using this monitor in my seed germination station.  I will be using an ESP8266 WiFi Arduino module along with a DHT22 temperature and humidity sensor to collect data.


Last summer I built some multi-purpose sensors to monitor the temperature and humidity around the house to determine if we needed a repair or replace our home heating and air conditioning system.  I put together the multi-purpose sensor on a breadboard as you can see in the image below.

My DIY Multi-Sensor Project
My DIY Multi-Sensor Project

In this project, I used a NodeMCU V2 ESP8266 (a WiFi enabled microcontroller controller) and connected it to a DHT22 sensor (shown in white above), a motion sensor and a photodiode for measuring light.  Finally, the NodeMCU connects to a MQTT server I have running in the house and the data is plotted in home-assistant.

Next, I’ll walk you through putting together a simple wireless temperature and humidity monitor that you can use around the house or in the garden.

Simple Temperature and Humidity Monitor

These are the things you will need:

  • NodeMCU V2 (or any other ESP8266 enabled board)
  • A DHT22 or DHT11 temperature and humidity sensor
  • A Breadboard (Optional)
  • A 1K Resistor
  • Solder (Optional)
  • Hookup or Jumper Wire
  • A 6V battery holder

Assemble the circuit according to the schematic below.

Temperature and Humidity Sensor Schematic
Temperature and Humidity Sensor Schematic

The connections are as follows:

For the DHT22 Sensor:

  • 1 connects to the NodeMCU V2 3.3V Output
  • 2 connects to  the NodeMCU V2 D2 Input
  • 2 connected to the 3.3V Output via a 1K Pull-Up Resistor
  • 4 is connected to the common ground.

And for the NodeMCU:

  • D0 is connected to the NodeMCU V2 RST Pin (for Deep Sleep)
  • VIN connected to 6V positive
  • GND connected to 6V negative

Try putting this together on a breadboard first to make sure you get the circuit right and solder everything together for a more robust permanent solution.

Once everything comes together, the final product will look similar to this.

Wireless Temperature and Humidity Sensor Monitor
Wireless Temperature and Humidity Sensor Monitor

The Code

Use the code below to set up a basic temperature and humidity monitor system.  The code publishes a JSON packet to your MQTT server every 10 minutes.  You will need to edit the essid, password, and server fields to match your network configuration.

After the board has been programmed it will send an update to the MQTT server every 10 minutes and go to a low power sleep mode after.

To program the board you can use the Arduino IDE or my favorite, PlatformIO.

The Sensor in Action

I placed this sensor inside of my cold frame and have been monitoring the temperature and humidity for the past few days.  This will give me an ideal of how hot it gets inside the cold frame and whether or not I need to automatically vent the cold frame if it gets too hot.

Cold Frame Temperature Data
Cold Frame Temperature Data
Cold Frame Humidity Data
Cold Frame Humidity Data

And there it is, a portable DIY Temperature and Humidity Monitor.  Feel free to leave comment if you like this post or if you have any questions.

Cold Frames – Mini Greenhouse for Seedlings

Cold frames are like magical mini greenhouses for seedlings.  They are used for acclimating your delicate seedlings to the variable weather conditions outdoors.  If you’re starting your seedlings indoors, a cold frame will maximize your seedling’s chances of survival.

As previously mentioned in my post about starting a seed germination station, I picked up a couple of books to help me with my vegetable garden this year and both of them provide extensive information on Cold Frames and how to use them.  I will be following the steps recommended in these books to use a Cold Frame to transplant my seedlings into the garden.

Week by Week Vegetable Gardener's Handbook

The Vegetable Gardener's BIBLE

The Weather

Now is not the time to transplant directly into the garden.  Last Tuesday the weather was terrible, we had sleet and freezing rain that closed many major roads and closed most businesses for the day.  Since I’ve already started a few plants, they will need a safe home during such adverse weather conditions.  Although the last frost is not slated until the end of March, I hope to have a few plants in the garden before then.  Hardening them off in a Cold Frame will maximize their chances of survival.

What is Cold Frame

I like to think of Cold Frames as miniature greenhouses.  Their purpose is to provide controlled warmth and shelter.  As you get your plants ready for the outdoors, you can either set them outside for short periods of time and increasing their time out until their acclimated, or you can use a Cold Frame and leave them outdoors.


Here are a few examples of cold frames.  If you’re handy, you can build one yourself, or if you have other priorities you can buy a pre-made kit.

Large Cold Frame
Large Cold Frame
Home Made Cold Frame
Home Made Cold Frame

Purchasing a Cold Frame

I decided to buy one this time around and ended up getting this one.

Small Cold Frame
Giantex Garden Portable Wooden Protection Cold Frame

It took about 10 days for the cold frame to arrive but it was worth it.  The Cold Frame came in a large wooden box and needed some assembly.

Cold Frame Package Contents
Cold Frame Package Contents
Cold Frame Assembly Instructions
Cold Frame Assembly Instructions
Assembling the Box
Assembling the Box
Adding the Lid
Adding the Lid
Fully Assembled Cold Frame
Fully Assembled Cold Frame

Now that the cold frame has been assembled, the next step is finding a good location for it. From what I’ve read this should ideally be a place that gets plenty of sunlight and is also protected from the weather on one side.

Cold Frame in the Garden
Cold Frame in the Garden

I placed my Cold Frame near the garden against the house facing South to get the most amount of sunlight possible.

Stay tuned – The Cold Frame is almost ready to be used.  I will follow up with a post on preparing the bed of the Cold Frame and managing the temperature inside the Cold Frame.

Starting Seeds Indoors – Automated Lighting

Starting seeds indoors requires a seed germination station and a lighting setup.  You will need to ensure that the lights are on for about 15 hours a day and to make life easier, its best to use a timer or other automated lighting setup.  In this post I will detail how I use a TP-Link Smart Plug to automate my lighting which I then can control from my phone.

When to Start Providing Light

Your seedlings will need light soon after their true leaves appear.  The true leaves will be the first leaves that appear on the growth outside of the cotyledon.

How to Use a Smart Outlet for Automated Lighting

I picked up a TP-Link Smart Plugs on a Black Friday sale from Amazon last year along with an Echo Dot.  This smart plug also provides the ability to monitor energy usage which is useful if you’re on a budget.

TP-Link Smart Outlet
TP-Link Smart Plug

If you recall in my previous post on setting up a seed germination station I used 4 foot T5 Grow Lights.  T5 lights are one of the most energy efficient lights you can use for your seed germination station.

I use the TP-Link Plugs all around the house to remotely control things like my 3D printer, desk lamps, humidifiers and my favorite of all – the coffee maker.  Uttering the phrase “Computer Coffee Maker On” is quite satisfying in the morning.

Now back to the point, seedlings will need about 15 hours of light each day until they’ve grown large enough to leave the seed starting station and begin their transition to the outdoors.  The lights should be positioned ideally about 2″ to 3″ above the seedlings.  To do this, use adjustable hangers to hang the lights.

Automating Your Lights using a Smart Plug

First plug the outlet into the wall and subsequently the grow lights into the outlet.

The light on the smart plug will turn green once it has connected to your WiFi network.

Next open the TP Link Kasa app on your phone and create a schedule for the lights.

TP-Link Kasa App Device Selection
TP-Link Kasa App Device Selection

Next, select your Smart Plug.  In this case I named my Smart Plug “seed lights”.

Configure two separate schedules for turning on and turning off the lights.

TP-Link Kasa - Turn on Schedule
Turning Lights On Schedule
TP-Link Kasa Turning Off Schedule
Turning Lights Off Schedule

Make sure to select every single day so that the lights turn on and off every day of the week.

TP-Link Schedule - Enabled
TP-Link Schedule

Turn on the lights and adjust the height of the lights to be within 2 to 3 inches of the highest growth.

Automated Lights with Hangers Adjusted
Final Setup with Adjusted Light Hangers

Your final setup will look similar to this.  Note that I kept the domes on as I still have a few seeds germinating.

Remove White Mold on Seedlings – Part 2

In this post I will follow-up with how to get remove white mold from seedlings and the flats.  I followed the simplest step in how to remove white mold on seedlings by scraping it off with a clean spoon.

See my previous post on how to prevent white mold from re-appearing.

Removing White Mold


  • A clean spoon

Simply scrape the white mold off the surface of the soil and discard.


White Mold Present
White Mold Present


White Mold Removed
White Mold Removed

Ventilate your trays and allow it to dry out between watering. If the humidity is high in the seed starting room, try adding some fans to increase air circulation.

White Mold on Seedlings – Part 1

Today, I found some white mold on my seedlings which are only 4 days old.  The white mold is mostly harmless but try taking few simple steps to avoid it and prevent it from reoccurring in the future.

Sprouts Emerging from the Soil

In my previous post I shared how to start growing seeds indoors with a seed germination station.  Everyday I check on my seedlings to see how they’re doing.  It’s been about 4 days since I’ve started this batch of seeds and the sweet basil seeds are just starting to emerge.

Sweet Basil Seeds Germinating
Sweet Basil Seeds Emerging

White Mold On Seedlings

When I went to inspect the chives, I found what appears to be white mold growing in a few of the flats.  You can see in the image below just to the left of center the white fuzzy mold.

White Mold on Seedlings
White Mold (front left of center)

This is a common problem in starting seeds that is high humidity and/or over-watering. If not taken care of, this will cause your delicate seedlings to die and may spread to other seedlings. This is definitely something to be avoided.

Mold Fighting Strategies

There are a few strategies we can try to reduce the humidity.

  • Air circulation with a fan
  • Propping up the dome

I’ll start with trying with propping up the dome.

Use Popsicle sticks or in my case Chopsticks leftover from last week’s Sushi bender to prop up the dome.  This should reduce the humidity inside. Now that the dome is lifted, I’ll need to monitor the soil moisture closely as the soil will dry out quicker.

Continue reading in my next post on what to do about the existing white mold.

Starting Seeds Indoors – Seed Germination Station

Use a seed germination station to get an early start on your vegetable garden this year by starting your seeds indoors.  In this post I will detail how I set up my own seed germination station using the steps detailed in the “Week-by-Week Vegetable Gardener’s Handbook” and “The Vegetable Gardener’s BIBLE”.

Now, this is the first time I’ve attempted this type of setup so feel free to read along and learn how do it yourself.  I’ve included links to the books I referenced below.  Read them for useful tips on planning and managing your own vegetable garden.

Week by Week Vegetable Gardener's Handbook

The Vegetable Gardener's BIBLE

The Final Product

Once you’ve completed the steps detailed in this post your completed seed germination station will look similar to this.  A seed germination station will help you get an early start on your vegetable garden when it’s too cold to sow your seeds directly in to ground.

Indoor Seeding Setup
My Indoor Seeding Setup

I’m currently using this setup to start some organic herb seeds i’ve purchased: slow bolting cilantro, sweet basil, and common chives.  The sweet basil and common chives sprouts should appear in 7 to 14 days while the cilantro will take 14-21 days.

How Does it Work?

Now why would you want a seed germination station?  As it turns out sowing directly in the ground requires that the soil temperature is warm enough to support germination.  If you want to start early, the ground may not be ready for your seeds, but that doesn’t mean you have to wait.  To simulate ideal growing conditions, a heating mat is used to warm the bottom of the trays.  Once the seedlings emerge, the lighting simulates the spectrum of light required for photosynthesis to occur and encourages growth of roots.  The dome is used to provide humidity and prevent the soil from drying out while the seeds germinate.

Building Your Own Seed Germination Station

To get started you will need supplies and equipment, most of which can be found at your local garden center or hardware store.

Supplies Needed

  • 48″ x 24″ x 0.5″ plywood board (not shown)
  • 48″ x ~20″ heating mat
  • 2 x 1020 Tray without drainage holes
  • 72 cell flats in each of the seeding trays
  • Soil-less potting medium
  • Seeds
  • Labels
  • Humidity Dome
  • 4′ Grower’s Light with Cool White Bulbs
  • Plywood Board 2′ x 4′ x 0.5″ (optional)

I purchased most of my supplies online from a few reputable retailers.  Here’s a shout out to GreenHouse Megastore which has great prices on growing supplies.


GreenHouse MegaStore

Here are a few links to other equipment used in my setup:
Grow Lights

Heating Mat

Your Seed Starting Location

Before you assemble your seed germination station, you will need to locate a place indoors.  The following should be considered when selecting a site:

  • Access to water
  • Cleanliness
  • Humidity (less is better)

I chose to start in my garage as I had a clean counter available and it was relatively low humidity.  You may also consider a counter in your kitchen or a guest bathroom.

Assembling Your Seed Germination Station

I started with placing a .5″x2’x6′ sheet of board on the counter and then placed the heating mat on top of the board.  My thought behind this is that it will provide some insulation and will keep water from pooling up underneath the heating mat in case of spills (which will happen when I water the seedlings).

Next I hung the lights from the ceiling using some adjustable hangers.  This will allow the lights to be as close to the plants as possible to simulate daylight indoors.

Following recommendations, I prepared all of the tools, flats, and surfaces by cleaning with a 1/10 bleach solution.  The reason you will want to do this is to prevent any fungi or bacteria from growing in your flats which can in turn kill your seedlings.

Next, I moistened the seed starting mix and packed the soil into the flats.  I placed the flats into the trays and then moved them onto the seed starting mat.

I followed the instructions on the seed packets to sow about 1/4″ beneath the soil and then covered the flats with the humidity dome.  Next, I set the temperature controller to 75 degrees Fahrenheit and turned off the lights.  The lights will come on when the seedlings emerge from the soil.

Note that I wasn’t specific on how to sow the seeds.  You may want to look for some YouTube videos on how to do this, as it can be done in a variety of ways.

Check back with me next week to see how the seeds are doing.