How to Start Seeds Indoors: Seed Starting Supplies

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“The home gardener is part scientist, part artist, part philosopher, part plowman.” -John R. Whiting

John Whiting was right. Gardening requires a diverse skillset, and research into many other areas of life outside of botany and biology. In fact, to the serious gardener, gardening actually starts long before you can plant seeds in the ground!

While planning their crops for the upcoming year, many gardeners rely entirely on seedlings grown at a local nursery or chain store. It’s a great way to get started, but it also severely limits your options, forcing you to plant only common varieties according to someone else’s planting schedule instead of your own.

That’s why once you’ve gotten the basics down, or you want to grow heirloom varieties that are 100% organic, you should start your own seedlings. Plant what you want, and you will know exactly what you’re getting and when they’ll be ready. Here’s how to start seeds at home.

How to Start Seeds at Home

Supplies Needed

Seeds
Containers – most commonly, gardeners use 1020 trays with humidity domes
Seed starting soil mix
Labels/way to track plantings
Watering can or another method of irrigating plants
Heat mat
Grow lights (w/timer is especially helpful, though technically optional)

Seeds

Of course, you can’t have plants without high-quality garden seeds first! 😉 Pick varieties that grow well in your climate, that benefit from a headstart indoors (beans and corn are planted directly in the garden, so you don’t need to start them inside), and that you will eat or preserve. Also, when choosing seeds, make sure you aren’t relying on very old seeds without testing their germination before planting. Plant a few of them in a moist paper towel, to make sure they’ll sprout properly.

You can learn more about choosing your garden seeds here.

Containers

You can start seeds in many different kinds of containers. If you look around at other growing systems, you might see growers using tray inserts, peat pots, peat pellets, and even soil block makers. You can also make your own custom containers, if you’re ambitious. Most gardeners just use use 1020 trays with humidity domes, depending on what you’re growing.

Tray inserts are usually made from plastic and come in two pieces. These “cells” contain drainage holes, so you place these cells in a solid plastic container for growing. (These are most commonly used for seedlings.)

Photo Credit: Steven Depolo on Flickr.

Peat pots are small pots that are made from peat. When you plant seedlings from peat pots, you plant the entire pot with the seedling, since peat breaks down into the soil. Peat pellets are little peat pots that expand when they become moist. (You can also plant the entire peat pellet with the seedlings, like a regular peat pot.)

With a soil block maker, you can eliminate the need for a container altogether. The soil blocks provide the form, while the roots provide the strength. These are easy to handle when transplanting, though soil blocking does use half or more peat moss in the soil mixture. and it does require proper moisture levels and mixing techniques in order to work properly.

Quick Tip: As you plant, you’ll also need a method for tracking what you’ve planted where. You can use plant labels or popsicle sticks that can be written on with a marker and then poked into the soil. Grid paper is also very helpful for tracking what you’ve planted in each cell. Don’t take it for granted that you’ll remember! Life gets busy, especially in the spring, and you don’t want to second-guess yourself later. 😉

Soil & Growing Medium

What kind of seed starting soil mix should you use? Different gardeners use different things, but here is the recipe we use:

Homemade Seed Starting Soil Mix:

4 parts screened compost (screen it through 1/4-inch screen to remove large bits)
1 part perlite
1 part vermiculite
2 parts sphagnum peat moss and/or coir

While purchasing seed starting soil mix in small bags gets expensive, greenhouse supply companies provide 30-40lb bags. Watch for sales (especially year-end sales) on sterilized seed starting mediums. (If you’re using a soil blocker, you’ll use a different mixture. Read more in our pottiong soil & soil block mix post.)

Germination Requirements

Germination requirements are conditions that must be met in order for your seeds to germinate.

Germination requirements will be listed on seed packages, and some seeds have more requirements than others. Strawberry seeds, for example, need very bright light. (Most seeds need light to grow, but there are probably a few plants that require dark conditions instead.)

Also consider required soil temperature and seed treatment. Tomatoes and peppers, for example, need very warm soil, 70-80 degrees! Occasionally, seeds may require soaking, stratification (a period of cold before germination), or scarification before they’ll germinate properly. Rhubarb, and morning glory seeds, for example, need soaked being planted. Though not very common, you’ll occasionally discover seeds with a tough outer shell that must be scratched (“scarified”) before they will germinate properly. This is easily done by rolling the seeds gently in folded sandpaper before planting. (This isn’t a common requirement, but you may run across it with some flower seeds.)

Just remember, your seed packet will usually mention if your seeds need special treatment before planting. Most seeds have a germination rate of 80% or more, but it does depend on how well you follow germination conditions.

Remember that regardless of germination requirements, it’s always better to have too many seedlings than not enough. Don’t be afraid to plant more than one seed per cup/cell/container. If too many seedlings grow, just plant the best seedlings and prune the weakest. You should always allow extra seedlings for transplant shock. And if you end up with too many extra in the end, you can always give them away or sell them!

Temperature

Most seedlings require warm, regulated temperatures to grow, so you’ll need to start your seeds near a heat source like a furnace. Some gardeners use heating mats that contact directly with plastic trays and keep the seedlings a consistent warm temperature. (One source suggests soil temperature should be 75 to 90 degrees F, but that if using heat mats, you should turn them off after the seedlings are mature.)

Light

In addition to the right soil and temperature, your seedlings need light to grow strong. Indirect sunlight is best if you’re already using window light, because direct sunlight is too intense and could bake your plants!

Many gardeners use fluorescent shop lights instead. They’re the cheapest lighting option and you can set them on a timer. (They work great, but they do need to be very close to your plants, within a couple of inches being ideal. Keep in mind you’ll have to adjust them as the plant grows.) You can also purchase commercial grow lights that produce a very bright light, though they are considerably more expensive.

There are many different kinds of grow lights available, including LED lights, which have become more accessible in recent years.

Once you determine what artificial lights you will use, you need a way to exposure your plants to the light. We use a shelving unit or a grow light stand.

Some Quick Tips & Considerations:

You’ll have to adjust the height of the lighting above the plants. You can do this with screw hooks and chains/paracord. (When your plants are small, they require more light, but you don’t want the plants to actually touch the bulbs either. Be careful and think ahead.)
Seedlings should get 16 hours of light/day to get the best start. This is where a timer comes in handy, especially if you’re not home or busy enough where you think you’ll forget.
Cover your seed trays with plastic dome covers, or the entire grow shelf with plastic, to help control moisture and humidity levels.

Moisture

Speaking of moisture, seeds and seedlings need water…just not too much, or they’ll rot and/or drown! To keep seeds moist during germination and maturation, provide consistent moisture. During their early days, you may want to lightly cover the soil too, so the moisture doesn’t evaporate and the soil remains warm. (This is why seedling trays often come with clear plastic covers on top.)

Use a pump sprayer or automated tools found a greenhouse supply company. One such tool uses a long, 8-foot PVC tube with emitters every foot or so. This is automatic, though you may have to check and adjust it from time to time. You can also use drip irrigation kits set on timer to flood the trays, dripping for 20-30 minutes at a time. You could even use a spray bottle! Or just a plain ol’ watering can works too.

Whatever system you use, you should always water from the base of the plant to prevent damping off.

Conclusion

You will need to order a few basic supplies, including seeds and containers, so shop around locally or online and see what you like best before you start seeds at home! Once you get them up and growing, you might be surprised just how easy it is to grow your own seedlings at home.