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10 Simple Tips for a Successful Indoor Seed-Starting Setup

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Hello Growers. It’s that time of year again. Spring is on the horizon, and it’s time to get our indoor seed starting setup figured out and our planting underway.

The tricky thing about growing seeds indoors is creating an environment that’s just right for germination and seedling growth. So the right indoor seed starting setup is critical. Below I’ll share my best tips for growing strong and healthy seedlings inside. And I’ll share my indoor seed-starting setup, which I put together for less than $230 with items from Amazon. 

The following tips all come back to the simple question: What do seeds need to germinate and grow into strong, healthy seedlings, ready to be transplanted into the garden? But it’s not all about the plants’ needs. Getting the right setup that is both affordable and convenient to use is also key to indoor seed starting success.

Tips for Seed Germination:

1. Pick the Right Growing Medium

For beginners, it’s easiest to start with a premixed commercial seed starting mix. The downside to this is that these mixes almost always contain peat moss, which isn’t great for the environment. If you’re new to gardening, pick one of these peat-based mixes and move on to tip number two.

If you’ll be starting a lot of seeds, and you’ve got some experience under your belt, consider using a peat-moss-free alternative.

The environmental problem with peat moss is threefold. First and most critically, peat bogs are huge carbon sinks, and when peat moss is mined, it releases large amounts of carbon into the atmosphere, accelerating global climate change. Also, peat moss is being mined at an unsustainable rate, and the mining process harms the ecosystem. For more information, check out A Case Against Peat, from the UGA Cooperative Extension.

When choosing a seed starting medium, avoid products containing peat moss. Here are my three best eco-friendly seed starting medium recommendations.

Finished, sifted, and sterilized compost

Use your own compost or some that you’ve purchased. Compost can be used straight or mixed with other things to improve drainage and water-holding capacity such as pearlite and coco coir (see below).

For indoor seed starting, you’ll want to sterilize the compost to keep fungus, pathogens, and gnats from becoming a problem. To sterilize, you have a few options, including a microwave, a conventional oven, steam, or even the sun. I go into great detail about how to sterilize soil in my post, How to Sterilize Potting Soil at Home.

Leaf Mold

Leaf mold is simply composted leaves. It takes some advanced preparation to get it in time for seed starting but is easy to make. Just rake up leaves from your yard (or take your neighbor’s) and leave them in a pile in a corner of your yard for about a year. The result is a crumbly soil-like material that’s great for starting seeds. Like compost, leaf mold should be sterilized before use as a seed starting mix.

Coco coir or coco peat

Coco coir is just coconut fibers. It’s widely available and affordable at garden centers and marketed as a peat moss alternative or seed starter. It comes compressed in a brick and rehydrates to many times its original size.

One warning about coco coir is that it may have salts in it that aren’t good for seedlings. Unless the package says it’s prewashed, it’s probably a good idea to rinse the coco coir with fresh water before sowing seeds into it. Coco coir also comes in pellets for easy planting. Just rehydrate the pellets in their tray, watch them expand, and sow your seed in the indent. 

2. Sow Seeds to the Proper Depth

If a seed is planted too deep, it could run out of stored energy before it breaks the surface and will die before it ever sees the sun. If a seed is planted too shallow or just dropped on the surface, it may not germinate because it’s either too dry or exposed to too much light.

Usually planting depth correlates to seed size. The bigger the seed, the deeper the planting depth. A rule of thumb is a depth equal to twice the seed diameter. But always check the seed packet.

Some seeds need darkness to germinate. Others germinate better with light. So know what your seed varieties prefer and, again, follow the seed packet instructions for planting depth.

3. Keep the Surface Moist without Over-watering

Seeds need consistent moisture for germination. Not enough water and they’ll dry out. Too much water and they’ll rot or develop mold. In the beginning, it’s important to keep the growing medium surface moist, so top-watering is better than bottom-watering.

Later on, once roots develop, bottom watering is effective, easier, and more foolproof.

How you apply water is just as important as how much. A standard watering can’s water droplets are too coarse and can disrupt small seeds, or even wash them away. Instead, use a spray mister for top-watering seeds and very young seedlings. A standard spray bottle set to the mist setting will do, but if you have many trays to water daily, it can get pretty tiring for your hand. A great alternative is a pump spray mister.

To keep the growing environment humid, cover the tray with clear plastic. Commercial covers are okay, but plastic wrap or a clear plastic bag set loosely over the tray or pot works even better. The goal is to keep the soil from quickly drying out, while still allowing airflow. You can reuse this plastic year after year.

If using a commercial cover, allow the containers to air out periodically to prevent mold from growing. A couple of hours a day with the cover off is a good idea. Or, just keep them cracked all the time.

Once the seeds germinate and you switch to bottom watering, a cover is no longer needed.

4. Apply Bottom Heat for Germination

One of the best things you can do to improve germination rates is to give your seeds a little extra warmth. You can get heating mats specifically for seed starting to put under the trays. This is important if you’re starting your seeds in a cool location, such as an enclosed porch, garage, or basement. But even if you’re starting them in a heated room, heat mats can be beneficial.

Sometimes seed packets will say what the optimal germinating temperature is. Some heating mats have adjustable temperature controls, but a basic one without fancy controls is fine.

After the seeds have germinated, a heat mat is no longer needed. Turn off the heat mats at this point because bottom heat is no longer needed and can even cause problems, like legginess in seedlings.

Tips for Healthy Seedlings:

5. Provide Sufficient Light 

After germination, all seedlings need light. A sunny window will work, but it’s not ideal. Seedlings grown this way get leggy and weak because they use their energy to grow long seeking better sunlight rather than growing thick and robust. You can mitigate legginess in seedlings grown on window sills somewhat by turning the tray every few days.

A far better way to avoid legginess is to get a grow light. These can be inexpensive and simpler to set up than you might think. For better energy efficiency, choose LED lights over fluorescent lights.

6. Maintain Moisture Levels

After germination moisture isn’t as critical as it is for germination, but you still don’t want your seedlings to dry out.

Check them daily and water them as needed, probably about twice a week if you’re bottom watering. Just pour a small amount of water into the bottom of the tray and it will wick up into the growing medium. Don’t fill it too high because it’s still possible to over-water this way. Pour out any water that isn’t absorbed after a few hours.

7. Provide Nutrition for Your Seedlings

Seeds contain all the nutrition required for the very beginning of a seedling’s life. But after the first true leaves develop, they will need outside nutrients. Especially if you planted in a nutrient-free medium like coco coir or most commercial seed starting mixes, you’ll need to provide your seedlings with nutrients.

Use an organic liquid fertilizer mixed in with water and use half the amount listed on the package.

Alternatively, consider making your own natural fertilizers. The Regenerative Grower’s Guide to Garden Amendments is a resource to learn more about this practice, with recipes for making amendments out of weeds, leaf mold, eggshells, bones, and other easily sourced items. These types of amendments are even better than chemical fertilizers because of all the micronutrients and living organisms they contain, which enrich soil well beyond just adding nitrogen, phosphorous, and potassium.

If you use compost or leaf mold for a growing medium, you may not need to fertilize, depending on how nutrient-rich your compost is and how long your seedlings will be inside before transplanting. Monitor your seedlings and if they look yellow or are slow to grow, consider feeding.

8. Harden Off Your Seedlings Before Transplanting

Before transplanting your seedlings into your garden, plan on taking a few days to acclimate them to the harsher outside environment. Skipping this step can lead to sun scalding and shock to the baby plants, and even plant loss.

Over a week, bring your seedlings outside for increasing lengths of time during the day. Put them up off the ground on a table or bench where it’s a little warmer and they’re safer from nibbling pests.

Ideally, start on an overcast day and put them in a shaded location. Each day, increase either the amount of sun or length of time outside or both. By the end of their hardening-off period, the leaves of the seedlings will have thickened noticeably. This thickening is a plant’s way of applying sunscreen, and it’s how you can tell they are ready for your garden.

Seed Starting Organization Tips

9. Make a Garden Plan

Having a plan for every plant you start indoors leads to greater success with your garden. Drawing a diagram of your garden and planting layout on a sheet of graph paper is helpful and can be fun, especially early in the season when spring growing enthusiasm is high but it’s still too early to start planting.

Learn more about planning your garden in my post, How to Plan Your Vegetable Garden Layout. In that post, you can also download my free printable garden planning PDF guide, which contains a dot grid sheet for drawing your garden layout and plant spacing guides.

Choosing Seeds

When you pick out your seeds for the year, consider which plants you like to eat the most and which ones are more expensive to buy. Choosing vegetables and herbs you eat often, or ones that you like but pay premium prices for at the grocery store or farmer’s market are going to be the plants you get the most value from growing in your garden. Of these plants, choose the ones that are suitable for your garden and climate.

To avoid stress at transplant time, make sure your garden beds are ready and each seedling to be transplanted will have a home. Plant a little more than what you plan to grow so that you’ll have enough in case some seeds don’t germinate or seedlings don’t make it. If you have extra plants, you can always give them to friends and neighbors, or even sell them.

10. Keep a Planting Record

It’s easy to forget what you planted where and when you planted it if you don’t write it down. At the very least, make plant tags and label them with the name of the plant and the date planted.

It’s also easy to forget to plant everything you planned on when the time comes if you don’t have a planting schedule. A paper or digital schedule and record of your sowing and transplanting activities is a great tool to keep you organized and your seed-starting activities on track.

To help schedule and record your planting, you can download my free printable seed starting tracker. Just enter your name and email address into the form below and I’ll send a download link to your inbox.

I made this tracker because I was unhappy with the other seed starting trackers available online. This one has all the information I need for keeping track of my seed starting, including a place to record the actual dates for each week before the average last and first frost dates.

My Indoor Seed Starting Setup

Now that we’ve covered my ten seed-starting tips, it’s time to show you my indoor seed-starting setup. I have a dedicated shelf on one wall in my dining room for all of my seed-starting and plant-rooting projects. See the image below.

The following list contains affiliate links to the products I used on Amazon. If you choose to buy these products to make your own seed-starting setup, I’d really appreciate it if you click through my links.

My simple setup for starting seeds indoors includes:

  1. Adjustable shelving organizer – easy to assemble, 30″ wide x 14″ deep with five adjustable height shelves.
  2. Full spectrum LED grow lights – This set includes eight lights that can be connected in serial and individually switched on or off. It includes supplies for three installation options: hardware, adhesive, and zip ties. I used the zip ties to easily mount one on the underside of three of the shelves, but you could do all four upper shelves. Update: If I were to purchase more lights, I’d get some with more lumens such as these T8 LED Shop lights with 4680 lumens. They are the same as the first set but put out more light for your plants.
  3. 24-hour mechanical timer for automating the grow lights so you don’t have to remember to turn them on and off. It’s simple, low-cost, and super easy to set by moving tabs up or down. It has two outlets, so you can plug in the lights and one heat mat at the same time.
  4. Seedling heat mats to improve germination rates. These are only needed until germination.
  5. Seed starting trays – these are the smaller trays shown in the picture (9″x14.5″). Note that three will fit on a shelf side by side, but only if you don’t put the clear covers on. That’s why I have a standard 72-cell tray (10″x20″) and a 40-cell tray together or two of the 40-cell trays together on one shelf. Update: I’ve since found that I don’t enjoy using the small 72- or 40-cell seed starting containers because I don’t like to pot up my seedlings before transplanting them out. Instead, I use 2.5″ or 3″ containers like these Extra Deep Landmark Nursery Pots.
  6. Hand-held pressure sprayer bottle – I got mine from my local nursery, so it’s different than the product linked here, but it’s very similar.

Conclusion

My best ten tips for seed starting are divided into three categories: germination, seedlings, and organization. For germination, choose the right seed starting medium, sow seeds to the proper depth, keep the surface moist without over-watering, and apply bottom heat. For healthy seedlings, provide sufficient light, maintain moisture levels, provide nutrition, and harden them off before transplanting outside. To organize your seed starting, have a good plan and keep a record of what you plant and when.

A good setup for indoor seed starting makes for happy plants and a happy gardener. The ten tips covered above will help you set up your indoor seed-starting area to get your seedlings and garden off to a great start.

Remember to grab my free seed starting tracker to help you stay organized this year.

Happy growing!


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