Do Humidity Domes Work? [+ Best Ones in 2021]

by Chenell | Last Updated: January 25, 2021

Starting seeds indoors for this years garden? The thing about seed starting is that you can make it as simple or as complicated as you want.

humidity domes

You can put seeds in dirt, water them and hope for the best – or you can get a full-blown seed starting kit with a heat mat, humidity dome, and high quality propagation tray, along with some soilless starting mix.

The difference is going to show in the length of time it takes to germinate, as well as the seed germination rate you end up with.

If you’re already putting in the extra effort and starting seeds indoors, you clearly want to get a head start on the growing season. So why not put in just a little more effort and get a higher yield and bigger harvest of plants for your garden?

Each of these components, while not necessary, have a specific purpose and help increase the germination rate so more of your seeds turn into seedlings. Let’s talk about that clear piece of plastic that looks like something commercial growers would use – the humidity dome.

What is a Humidity Dome?

A humidity dome is a clear piece of plastic that sits on top of a seed tray to capture moisture and keep your seed warm during the germination process.

Most seeds sprout best between 70-85 degrees Fahrenheit, and since the average home is not this warm your seeds might need a little help to get started.

Note: you can still germinate seeds at lower temperatures, but the process will take quite a bit more time to get going.

Many people turn to seedling heat mats as a way to help keep the temperature up, but using a humidity dome in addition to the heat mat will trap moisture that would have otherwise evaporated. This means you won’t have to water your seeds as often during the seed starting process.

The Benefits of Using a Humidity Dome

There are a few reasons you might want to use a humidity dome when seed starting indoors:

  1. Increase germination rates for your seed
  2. Maintain moisture levels so you don’t have to water every day
  3. Setup the perfect environment for seeds to germinate

Using a humidity dome is a great way to help your seeds germinate, especially if you’re using older seeds that might have a lower chance of germinating than newer seed.

Now you know what humidity domes are used for and some of the benefits of starting seed with them, but there are a few common questions that come up as well.

Is a Humidity Dome Necessary? Should I Cover My Seed Trays?

A humidity dome is not necessary for germination. A seed will still germinate without a humidity dome – however, using a dome on top of your seed trays can help you get higher germination rates with your seed.

They can also help speed up the germination process and reduce the need for you to constantly ensure your seeds have enough water to grow.

Domes will keep the relative humidity levels in the tray at ~98%, which is ideal for seed starting.

Does A Humidity Dome Need Holes/Vents?

The simple answer is that a humidity dome doesn’t need holes.

The holes are helpful if you need to vent the humidity a bit. Too much humidity can lead to mold in your seed trays, which is definitely not something you want.

Generally, you’ll only have the dome on for a few days until seeds being the process of germination. If you’re starting seeds for a plant that takes a little longer to germinate, then mold might be a problem you can encounter and you’ll want to consider getting one with ventilation holes.

In that case, you’ll want to get a dome with ventilation holes to help avoid moldy soil and fungus on your seed.

When To Vent Humidity Dome

You’ll want to start thinking about venting the tray if it takes more than 5-7 days for your seed to germinate. At that point, mold and fungi might be creeping in so you’ll want to get some air flow going and release a bit of that humidity and heat.

When to Remove Dome From Seedlings

Remove the humidity dome once your seed germinates, i.e. once it starts turning green. These domes are used to help with germination rates, so once that happens, their job is done. You’ll want to check the seeds every day for signs of germination, and when you see green sprouts coming out, it’s time to remove the dome.

If you leave the dome on too long you can kill your seedlings by causing rot and/or fungal diseases.

Similar to the hardening off period where you gradually expose your plants to the outdoor elements, you might want to do the same here. The first day you can open the vents, and then leave the tray propped open for a day or two before removing the entire thing.

This will help make sure your plants don’t go into shock after going from a warm, humid environment to one with a little less heat and a lot less humidity.

How Do You Prevent Mold When Starting Seeds With Humidity Domes?

Preventing mold is definitely something to consider when you’re using a plastic dome to trap moisture in. Since you’re only keeping the dome on the tray for a few days, you shouldn’t encounter mold. But problems do come into play if you leave it on longer than that.

You can start opening the vent holes if you need to keep the dome on longer, allowing some air to flow around the tray and reduce the probability of mold.

Do You Need Light To Germinate Seeds In A Humidity Dome?

A seed does not need light during the germination process to actually turn into seedlings. Germinating seeds can be done in the dark, as they only really need water and heat to start growing.

However, once the seeds being germination, they are going to need quite a bit of light to turn into healthy seedlings for your garden. In addition to a heat mat to bring the temperature up, you’ll want to start considering getting some grow lights for your seedlings to keep growing strong and healthy. A seedling needs more light than you think!

DIY Humidity Dome: How To Make Your Own

When using a humidity dome, it’s a good idea to only plant one variety of plant in the tray. Germination rates are very different for each variety so if you plant all of the same kind in a tray, you won’t have to worry about removing the dome too soon once one germinates.

Egg Carton

This method almost requires you to sow your seed in the bottom of the egg carton and use the lid as the humidity dome. Plastic egg cartons will keep more of the water in, as a typical egg carton is going to absorb a lot of that water.

The problem with this method is that your seeds don’t have as much space to grow. After they germinate, they’re only going to be able to stay in that container for a short time before needing to be replanted into a larger pot with more space.

Plastic Wrap or Plastic Bag

You can use plastic wrap or plastic bags to create this effect as well. Simply cover your seed tray with plastic wrap, making sure there are no spaces being created between the tray and the plastic wrap.

Because the height of the wrap wont allow much air circulation to happen, you’ll want to keep a really close eye on the environment to avoid mold.

Moist Paper Towel

This is probably the easiest type of solution. Using a moist paper towel helps keep the humidity high, but also have some more ventilation than plastic does so you wont have to worry about fungi and mold as much.

Things to Keep in Mind When Choosing a Humidity Dome

  1. Buy the humidity domes from the same brands you get your propagation trays from. A lot of 10×20 trays are not actually 10 inches by 20 inches – they’re often a quarter or half inch wider or longer. This will become problematic if you don’t get the domes from the same place you get your trays.
  2. Get a dome with vent holes if you’re going to be growing a seed that takes more than 5-7 days to germinate.

Best Humidity Domes for Seed Starting

There are a few options when it comes to humidity domes that you can buy. You can get some that are really tall or more shallow, some have vent holes and some do not.

The most common type is a 2 inch dome, but you can find them as tall as 7-8 inches high. For most gardeners, the height really wont matter too much as you’ll be remove the dome once seeds begin germination.

Here are some of the best humidity domes I’ve found.

EarlyGrow Domed Propagator Kit

This dome has all kind of vent holes and will be great if you’re growing plants from seed (or clones if you’re a different type of gardener 😉 that needs a high humidity environment for longer than just the germination process.

This dome kit allows you to buy extensions to make the dome even taller as your plants grow.

EarlyGrow Domed Propagator with Vented Sides
$32.39
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06/19/2021 02:17 pm GMT

Hydrofarm 7.5″ Humidity Dome

Jump Start Germination Station with Humidity Dome

Jump Start Germination Station w/Heat Mat Tray with 2" Dome
$30.13
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06/19/2021 02:20 pm GMT

This is a great option if you need a full seed starting kit. It comes with:

Bootstrap Farmer Humidity Dome

This is going to be a higher quality starter kit, but you will still need to buy a heat mat separately as it doesn’t come with one.

Top Pick
Bootstrap Farmer Seed Starting Kit

Bootstrap Farmer is a brand that has high quality products for home gardeners and growers. This kit includes:

  • 2 Extra Strength Microgreen Trays With Holes
  • 2 Extra Strength Microgreen Trays No Holes
  • 2 Humidity Domes Extra Strength


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This dome comes with vent holes to allow you more control over the moisture levels inside the seed tray.

The Bootstrap Farmer products are always of a high quality, so you can’t go wrong here. They will last you a long, long time. However, their are quite a bit more expensive than other options, and since gardening can get quite expensive already you’ll have to make that decision between quality and price.

Super Sprouter Propagation Kit

This is a seed starting kit that comes with a humidity dome. As I mentioned above, you’ll want to get your domes from the same place you get your cell trays, so you might as well buy them together.

Super Sprouter Premium Propagation Kit with Heat Mat, Tray, 7" Dome & T5 Light
$79.95
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06/19/2021 02:17 pm GMT

Starting seeds in trays is a great way to get a jump start on your growing season and produce bigger plant yields that you can transplant into your garden.

While using humidity domes to germinate your seeds isn’t necessary, it can be a big help in terms of getting more plants to grow.

Chenell lived in a big city for 9 years and loved it. But ever since she was a little kid watching her grandfather raise cattle and pigs, she's always wanted to live on a farm. Once the pandemic hit, she bought a house with her partner on an acre and half of land and started planning a 50 foot by 50 foot garden....with no experience. This site is the place where you can follow along as this millennial tries to learn to grow her own food (and eventually make her own avocado toast).