No-Fuss Supply List for Indoor Seed Starting

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If you’re thinking about starting your own vegetable/flower garden plants from seed this year, I’ll give you several reasons to go for it:

First, you have a lot more options to choose from when shopping for seeds than you do when buying seedlings. You can get your hands on rare and unique heirloom varieties you probably won’t find at a garden store or nursery, and you can search for hybrid cultivars bred for resistance to specific pests and diseases you have trouble with in your garden. That can give you a real advantage, compared to gambling with whatever seedlings are available on store shelves.

It’s also an uplifting experience to watch the tiny seeds you planted sprout and develop into productive plants. I believe it’s a proven fact these days that growing things and working in the garden has a positive effect on your mental health. Growing your own seedlings inside means you get to reap those benefits a lot earlier, while it’s still too cold to be out in the garden much.

Finally, starting your garden from seed saves you a significant chunk of money. Seeds are a fraction of the price of starts, at $3-$5 per packet. That’s the low end of what you’ll pay for a four-pack of nursery starts, and you’ll get at least 20 seeds, maybe more. You don’t have to spend much up front on equipment, either; you don’t need anything fancy or expensive to get started.

In this post, we’ll go through which supplies you absolutely need to have for your indoor seed starting setup, plus some optional things you might want depending on the space you’re working with.

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The Essentials

You can be as thrifty and creative as you want with your seed-starting setup, as long as you have the necessary framework. If you ask me, these are the non-negotiable supplies and equipment needed for successfully raising seedlings:

Seedling Pots/Containers

Obviously you’ll need containers to plant your seeds in, but let’s talk options and specs. While you can buy special seed-starting kits with features like domes and self-watering systems, using cheap or free/upcycled containers will work just fine. The most important things to consider when rounding up your pots are size and drainage.

The Importance of Container Size

The bigger your containers are, the more soil you’ll need to fill them. Hence, the more money it’ll cost. You’ll also want to think about how much space you have, since some container options are more space-efficient than others. Seedling tray inserts with multiple cells take up considerably less space than individual containers like solo cups. Just keep in mind that the smaller the container size, the sooner your seedlings will need to be transplanted or moved into larger pots.

Container size also plays a role in good germination and seedling health. For starters, small cells or containers can benefit seedlings that need consistent warmth to sprout and grow. That’s because a smaller amount of damp soil is easier to keep warm, either by room temperature or with a heat mat. Soil that stays too cold in the middle of a big container can cause cold-sensitive plants to struggle.

Smaller containers also lower the risk of over-watering, especially for seedlings that take longer to develop a strong stem and root system, such as peppers. If their pots are too big, the soil is more likely to stay soggy for too long after watering. That situation can smother delicate baby roots and cause stunting, yellowing, and even seedling death. I like to start slower-growing veggies such as tomatoes and peppers in 2-inch cells. Then, I’ll pot them up into larger containers once they’re big enough.

Small containers aren’t the go-to option for everything. Cucurbits like squash and cucumbers are fast growers that don’t like having their roots messed around with, and they’ll have a harder time bouncing back than other plants if those roots get too cramped. They do best when started in containers that are big enough to hold them until they can be planted out.

As you gain experience starting your favorite plants from seed, you’ll get a handle on what size pots work best with your process and setup.

Tips for Choosing Containers

If you’re going the DIY/upcycled route, your containers should be thin enough you can easily poke drainage holes in them. Test one and make sure your holes are big enough before you plant the seeds. Water should flow freely from the bottom whenever the soil gets a drenching.

Good picks for cheap or free/upcycled seedling containers are:

• Solo cups
• Dixie cups
• Egg cartons
• Recycled plastic containers like yogurt or pudding cups
• Really any small container you can easily poke holes in

A word on biodegradable pots:

Thinking about using homemade newspaper pots, cardboard egg cartons, or the little compostable pots sold in stores for seed-starting? While I generally love the idea of avoiding plastic, there are a few problems to be aware of.

First thing is, paper-based pots become little mold factories when they’re filled with damp soil. The several times I’ve used paper seedling pots, they were covered in fuzzy white mold within a few weeks, like the kind you might see on produce you forgot in the fridge. This happens because mold loves to grow on organic materials- in this case, the paper.

Mold like this usually isn’t harmful to the seedlings. But it is harmful to humans who have mold allergies (me) and it’s not great for aesthetics, either…

The second problem with paper pots is that they’re not great at maintaining moisture. Because of how porous paper is, the soil dries a lot faster and often needs watering more than once a day. This makes it easier to accidentally let your seedlings dry up completely. It also means they’re dealing with constant fluctuations in soil moisture, which causes plant edema and stress in seedlings.

Now, about those cute biodegradable seedling pots you’ll find in department store garden sections. The labels on these pots say they can be planted along with the seedling to prevent transplant shock, claiming they’ll break down as the plant grows.

That is straight up bad advice, folks. Young annual plants grow way faster than that thick paper will decompose in the soil, and they’ll get rootbound and stunted by these pots every time. It’s always best to peel the pots away from the root ball before planting. Trust me, do not plant the “plantable” pots!

If you get to a point where you’re starting dozens of seedlings indoors (you probably will), consider investing in higher-quality plastic pots and cell packs. In my opinion, something that can be re-used for many seasons is the most sustainable option when you raise a lot of seedlings.

Seedling Trays

For easier handling and watering, you’ll need trays to keep your seedling containers in. Standard nursery trays meant for seed starting are pretty inexpensive to buy. Some have holes in the bottom, and some don’t. You’ll need the kind without holes for indoor seed starting, since you don’t want excess water spilling everywhere at watering time. Hole-less trays are also a must if you plan to bottom water your seedlings.

If you’d rather use something you already have, a cookie pan or roasting pan will work as long as the seedling containers have a way to drain properly. Nursery trays usually have grooves and ridges on the bottom to prevent seedling containers from sitting in excess water. I’ve used a cooling rack in a shallow roasting pan when I was short on trays.

Seed-Starting Mix

Steer clear of garden soil or regular potting mix for your indoor seedlings. Soil from outside can bring in germs your pampered little plants aren’t ready to deal with yet, not to mention sneaky pest insect eggs. Bagged potting mixes are usually too “heavy” for potted seedlings. Some also have added fertilizers that are too intense for them in the first stage of growth.

For best results, get a bag of soilless seed-starting mix at garden or hardware store. This kind of mix is light and fluffy and will hold moisture without staying soggy, which is what newborn seedling roots need. Most options cost less than $10 per bag (and one bag goes a long way).

You can also DIY your seedling mix. However, the ingredients for that are only cost effective if you buy them in bulk. You might want to do that at some point, if you plan on raising hundreds of seedlings, but the bagged mix is more practical for anyone just getting started.

Unfortunately, the increased demand for gardening supplies has created some quality control issues in recent years. Some companies are using wood and bark chips to bulk up their soil mixes, calling it “compost.” This has mostly been an issue with bagged potting mixes, but lately I’ve found it in seed-starting mix too.

A proper seed-starting mix should not have large chunks of anything hard or woody, as this will cause poor seed-to-soil contact and low germination. It should be soft and even-textured. If you end up with something that looks like it’s mixed with landscape mulch, take it back and get something else.   

Grow Lights

You’ve probably heard you can put your seedlings in a south-facing window, if you don’t want to fool with grow lights. The problem is that seedlings have a tendency to stretch dramatically towards the light source whenever the lighting is uneven. A good example of uneven light is a bright window with a darker room behind it.

When they focus their energy on elongating to reach the light, your sprouts will become “leggy.” They’ll have weak, floppy stems and underdeveloped leaves. They may not outgrow these setbacks if the problem isn’t fixed quickly. Grow lights placed above seedlings give them even light coverage so they can focus on growing thick, strong stems.

Tips for Choosing Grow Lights

Grow light setups range from $15 for table-clamp lamps to $100+ for high-intensity LED panels and shelf systems with built-in light bars.

High-powered, expensive grow lights are only necessary if you’re growing plants to maturity indoors. You don’t need to spend a fortune on anything like that if you’re only planning to grow transplants for your garden. The budget options provide small seedlings with all the light they need until they’re big enough to go outside. You can also use T4 florescent shop lights (though they’re getting harder to find lately with the popularity of LEDs).

Cheap grow lights tend to have a smaller area of light coverage, which can cause seedlings on the edge of a tray to stretch inward some. It’s really no big deal. If you notice it happening, just shuffle the seedlings around once a day or so and let them take turns. I’ve found that when it comes to budget grow lights, the hanging bar lights tend to provide the most even lighting. Wire racks like the ones in my seedling room make hanging bar lights easy, and they’ll save you some space, too.

Seriously, don’t skip the grow lights, y’all. They are well worth the small expense.

Water-Soluble Fertilizer

Most annual seedlings will grow best with a fertilizer routine, especially those slow growers that have to be kept inside for longer. The first leaves that emerge- the seedlings’ cotyledons- provide everything a little sprout needs in the first stage of growth. But once it has its first set of “grown-up” leaves, it needs nutrients from the soil. Since most seed-starting mixes are sterile, soilless growing mediums, fertilizing is necessary at this point to prevent nutrient deficiencies.

Always use a water-soluble fertilizer, not a granular one. Granular fertilizers aren’t immediately available to the plants, and organic ones need soil organisms not present in a soilless mix to break them down. Water-soluble options are easiest for your seedlings to use.

Read this post to learn more about fertilizing your seedlings: How to Fertilize Seedlings (and Why You Should).

Plant Tags or Markers

Finally, you’ll need a way to label your seedlings. Otherwise, it’s really easy to get things mixed up, especially if you’re starting more than one variety of each plant. You can buy little plastic plant labels that stick down in the soil for this. Or, you can get creative and use what you’ve got laying around. I’ve used multi-colored paper clips when I ran out of plant tags (just don’t forget to write down what each color is marking).

Some Optional Stuff

While they aren’t required to grow healthy seedlings, here are a few things that might be helpful, depending on your situation:

Heat Mat

A seedling heat mat can help speed up germination for seeds that like higher soil temperatures. If you don’t have one, you can put your seedling trays in a naturally warm location in your house instead. Heat rises, so any area close to the ceiling, such as on top of a high shelf or your refrigerator, is often warm enough to work.

Most seeds don’t need light to sprout, so you don’t need to worry about grow lights while you’re waiting for germination (there are a few exceptions, so always read the seed packet before using the fridge-top method). Once you see sprouts poking through the soil, move the trays under your grow lights.

When heat mats are most helpful:

If you’ll be raising your seedlings in a drafty environment or somewhere that gets chilly on cold nights, such as a basement, a heat mat is probably worth the expense. You can use it for both germination and making sure the root zone doesn’t get too cold once seedlings have sprouted. Seedlings that don’t like cold soil will especially benefit from the added warmth.

My little “grow room” is in an older house that doesn’t have central heat and air. Since it’s not economical to keep it toasty warm during February and March, I use a heat mat to keep the soil temperature stable for my heat-loving seedlings. That’s a lot easier on the power bill than running a space heater on full blast. 

There is a small caveat to using heat mats post-germination. A typical seedling heat mat can easily run at 80F or so, when un-regulated. That much heat can cause seedlings to become leggy. If you want to provide your seedlings with bottom heat beyond germination, you’ll need to get a seedling heat mat with a soil probe thermostat. 75-80 is perfect for germinating heat-loving plants, but the thermostat should be turned down to below 75 once they’ve sprouted. 

Humidity Dome

These clear plastic domes fit over seedlings trays and are meant to hold in moisture and warmth to improve germination time. Think of a “greenhouse effect.” The drawback to humidity domes is that they reduce airflow around your seedling containers. That creates conditions that are ideal for mold development or, worse, damping off disease.

Personally, I only use humidity domes in very specific instances. I’ve found that they help speed up germination for superhot pepper seeds, which are notorious for taking forever. Otherwise, the domes cause me more trouble than they’re worth.

Humidity domes may be most useful if you have super low humidity in your house, which might be the case if you heat with a wood stove or electric heat pump. Still, you shouldn’t have any trouble germinating seeds without one as long as you keep the soil consistently moist.

If you do want to use a dome, the rule of thumb is to remove it as soon as you see the first sprout breaking the soil. Leaving it on for any longer can lead to damping off, a fatal seedling disease.

This post has some more info about heat mats and humidity domes: Using Heat Mats and Humidity Domes for Seed Starting: Everything You Need to Know.

Fan

An oscillating fan placed near your seedling trays can jump-start the hardening off process, since it simulates the wind they’ll experience outside. The added airflow can also help prevent mold and algae from forming on the seedling soil.

Any oscillating fan will work, but make sure to position it where it isn’t too intense on the seedlings. You’re going for a little breeze, not a windstorm. Running it a few hours per day should be plenty, if your growing area already has good airflow. I have my fan running on low 24/7, since there’s no central heat/air in the house, but I only direct it at the seedlings for three hours or so in the afternoon.

Final Thoughts

While this supply list applies to pretty much any plant that can reasonably be grown from seed and later transplanted, there isn’t a one-size-fits-all approach to the process. Different plants have different needs and preferences. The more plants you grow from seed, the more you learn about what works for them in your environment and what doesn’t. That being said, here are some common beginner mistakes you can avoid.

Do you want to raise your own seedlings, but you don’t have much space? Or, maybe you just don’t want to commit part of your house to grow lights and seedling trays? You can make a mini greenhouse out of a clear storage tote and keep them outside! This works for many types of plants, and I’ll show you how to do it here.   

If you’re ready to start browsing for garden seeds this post has some handy tips for decoding seed lingo and picking varieties that’ll work out best for you.