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Humidity Dome for Seedlings: Do You Need It & How to Use It?

How to Use Humidity Dome for Seedlings

How do you increase a seed’s germination rate? Try using a humidity dome. 

Although humidity domes are not a requirement for germination, using them helps create the ideal environment for the seed to sprout. It traps heat and moisture that speeds up the seed germination.

So, if you’d like to know more about humidity domes and how they keep your seedlings healthy, keep reading to give your seeds the best possible start!

What is a humidity dome?

What is a humidity dome
Image: Crop King

A humidity dome is a clear cover placed on a seed tray to create and maintain a humid environment, which is ideal for germination. It retains moisture levels, which prevents the seeds from drying and traps heat to speed up germination. 

They are helpful gardening tools because they increase germination rates and result in healthier seedlings, especially when starting them indoors.

There are three common types of humidity domes according to shape: round, square and rectangular humidity domes. Here’s a table on which plants you can use each of them.

TypeBest For
Round Humidity DomeSeed traysSeeds in individual pots
Square Humidity DomeMedium-sized seed trays
Rectangular Humidity DomeLarge seed trays
Growing vegetables

Round humidity domes are this gardening tool’s most common and versatile type. They are best used for small seed trays or when starting seeds in individual pots. 

On the other hand, you can use square humidity domes if you have medium-sized seed containers. They’re a great choice to create a more organized and compact garden space.

Finally, rectangular humidity domes are recommended for large seed starting trays. They’re best for plants that grow tall or have long roots.

Advantages and Disadvantages of Humidity Domes

Advantages and Disadvantages of Humidity Domes
Image: Desert Cart
Faster GerminationLeggy Seedlings
Seed ProtectionFungal Disease
Higher Germination Rate

Ultimately, humidity domes maintain the ideal moisture levels in the soil that help seeds germinate quickly. Moisture keeps the seed coat soft, making it easier to break open and allow the seed to sprout. 

Humidity domes also help protect the seeds from pests and diseases as it serves as a barrier that prevents these harmful beings from reaching them. Since they prevent seeds from drying out, humidity domes effectively increase their germination rate.

On the other hand, too much humidity might cause leggy growth in seedlings because they will try to stretch and reach toward the light. So, you should still regularly ventilate your humidity dome to prevent leggy seedlings. 

High humidity can also be a breeding ground for fungi that cause plant diseases. To prevent this, the moisture level inside the humidity dome should still be regulated while the seedlings are watered from the bottom.

How To Make a Humidity Dome

How To Make a Humidity Dome
Image: Mall Five

You can create your humidity domes by just using household materials. Here are different ways to make a humidity dome. 

1. Container and Plastic Wrap

Container and Plastic Wrap
Image: Mess for Less
DifficultyEasy ●○○○○
Duration5 minutes
Things You Need

Clear plastic containers, such as a plastic food container or plastic cup
Sheet of plastic wrap
Rubber band or tape

How To Do
1. Wash the plastic container and wait for it to completely dry.
2. Cut a sheet of plastic wrap. Make sure it’s larger than the top of the plastic container.
3. Place the sheet at the top of the container. Secure the sheet in place using a tape or rubber band.
4. Use it to cover a seed starting container or tray.

2. Paper Towel and Plastic Bag

Paper Towel and Plastic Bag
Image: Garson and Shaw
DifficultyEasy ●○○○○
Duration5 minutes
Things You Need
Paper towel
Plastic bag
Rubber band or tape

How To Do
1. Get one piece of paper towel and fold it in half lengthwise.
2. Moisten the paper towel.
3. Place a few seeds in the paper towel.
4. Place the paper towel in a plastic bag. 
5. Expose the plastic bag in a sunny place and seal it with a rubber band or tape.

3. Egg Carton and Plastic Wrap

Egg Carton and Plastic Wrap
Image: Valley Vet
DifficultyEasy ●○○○○
Duration10 minutes
Things You Need
Egg carton
Sheet of plastic wrap
Rubber band or tape

How To Do
1. Cut off the top of the egg carton.
2. Cut a sheet of plastic wrap.
3. Make sure it’s slightly larger than the bottom of the egg carton. 
4. Place the plastic wrap at the bottom and cover up to the top of the egg carton. 
5. Secure the plastic wrap using a rubber band or tape.

4. Tray and Plastic Bottle

Tray and Plastic Bottle
Image: Reddit
DifficultyEasy ●○○○○
Duration15 minutes
Things You Need
Shallow seed tray
Plastic bottle
Knife or scissors
Rubber band or tape

How To Do
1. Cut off the bottom of the plastic bottle using a knife or scissors.
2. Place the bottle upside down on your shallow seed tray. 
3. Secure the bottle using a rubber band or tape.

5. Food Container and Lid

Food Container and Lid
Image: Sometra
DifficultyEasy ●○○○○
Duration10 minutes
Things You NeedFood container with a lid
Rubber band or tape

How To Do
1. Wash the container and the lid. Wait for it to dry out completely.
2. Punch a small hole in the lid.
3. Cover the container with the lid. 
4. Secure the lid in place using a rubber band or tape.

How to Use a Humidity Dome

How to Use a Humidity Dome
Image: Grow Wherever

Now that you’re done making your humidity dome, it’s time to follow these steps to make sure your seeds will germinate fast and grow into healthy seedlings. 

DifficultyEasy ●○○○○
Duration5 minutes
Things You NeedHumidity dome
Seed starting mix
Potting tray
Spray bottle

How To Do
1. Fill the potting tray with your chosen seed starting mix.
2. Sow the seeds by lightly pressing them into the soil.
3. Mist the seeds with a spray bottle once or every other day.
4. Do not overwater the seeds. 
5. Place the humidity dome on top of the potting tray.
6. After a few days, vent the humidity dome for a few hours each day to prevent the humidity from getting too high.
7. Once the seeds have germinated, remove the humidity dome. 
8. Keep the seedlings watered and fertilized.

How do you prevent mold when starting seeds using humidity domes?

How to prevent mold when starting seeds using humidity domes
Image: Grower’s Solution

Although humidity domes are an excellent way to help seeds germinate, humid environments are also ideal for mold growth that can kill seedlings. 

But don’t worry because we’ve listed some tips on preventing mold growth when starting your seeds under humidity domes.

1. Punch holes in your humidity dome.

Punch holes in your humidity dome
Image: Etsy

Mold grows when the air is moist and stagnant. So, by using a humidity dome with holes, there will be better air circulation, and you can prevent the humidity level from becoming too high.

Just make sure that these holes are small enough to prevent pests, bacteria, fungi and viruses from entering the dome and attacking the fragile seedlings. 

2. Vent the humidity dome.

Vent the humidity dome
Image: Amazon

Ideally, you should vent your humidity dome every after watering because the humidity level increases under the dome when you water the seeds. 

So, venting them will reduce humidity and eventually prevent mold growth. You can do this by opening the vents or lifting the lid slightly once or every other day.

3. Avoid overwatering the seeds.

Avoid overwatering the seeds
Image: From Soil to Soul

Too much water will not only drown your seeds or make your soil soggy but also create a perfect environment for mold growth. 

So when you water the seeds, make sure to mist them just until the soil is moist. A good practice will be sticking your finger into the soil and checking if it’s still moist or dry to touch. 

4. Use a sterile potting mix.

Use a sterile potting mix
Image: Plant Care Today

Mold spores are commonly found in the soil, so using a sterile potting mix is highly recommended when starting seeds. This will help prevent mold growth in your seed starting tray or container. 

5. Clean the humidity dome regularly.

Clean the humidity dome regularly
Image: GFloutdoors

Keeping your humidity dome clean will also remove any mold spores that may enter your seed starting tray or container. Using a mild bleach solution and a damp cloth, just wipe down the inside of the dome regularly. 

When do you remove the humidity dome for seedlings?

When do you remove the humidity dome for seedlings
Image: Plus Manga

You should remove the humidity dome when the seedling develops their first set of true leaves, when they’ve grown about two inches tall, or when you start hardening off the seedlings or see any mold or mildew.

When the seedlings develop their first set of true leaves, it means that they’re already strong enough to survive outside the humidity dome. 

On the other hand, when they grow about two inches tall, you’ll need to remove the humidity dome to give the seedlings more space to grow and prevent them from becoming leggy and susceptible to wind damage or pest infestation. 

Another instance of removing the humidity dome is when you start hardening off the seedlings. Removing the humidity dome will help the seedlings adjust to the cooler temperature and drier air outdoors. 

Finally, when you see mold or mildew, remove the humidity dome immediately and clean the seedlings to prevent damage. You can also add fungicide to the potting mix to block the growth of other harmful pathogens that might kill the fragile seedlings.

FAQs on Humidity Dome for Seedlings

Does a humidity dome need holes?

Generally, humidity domes do not need holes because they primarily trap heat and moisture under the cover. However, when humidity domes have holes, it allows for proper ventilation, preventing high humidity, fungi and mold growth. 

Do seedlings need airflow?

Seedlings need airflow to distribute heat and moisture evenly. Proper air circulation also prevents the growth of mold and mildew that kills seedlings.

Do grow lights increase humidity?

Grow lights do not increase humidity but lower humidity by drying out the air. So, regularly mist your seedlings when placing them under grow lights.

What are the three conditions necessary for germination?

For effective seed germination, seeds should get enough water to absorb nutrients, adequate heat to activate enzymes that signal the germination process, and oxygen to start their food production processes.

Do seeds need sunlight to germinate?

Seeds need only indirect light to germinate. Sunlight helps in the germination process by warming up the soil.

Do you need light to germinate seeds in a humidity dome?

Seeds need light to germinate seeds, even under a humidity dome. However, they only need indirect light or grow lights to start their photosynthetic process and get the energy they need to grow. 

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