Starting Seeds Indoors for Spring Planting

Starting Seeds Indoors for Spring Planting

It’s spring and it’s time to begin starting seeds indoors. Spring is here! Some of the birds have returned with their courting songs.  As the days get longer we feel the warmth of the sun on our faces. The tulips are up, the tress are budding.

But the reality is for most of us that we have a another month or more of frosts before its officially time to enjoy gardening outdoors again.

Luckily, you can get a taste of spring by starting your garden now. In fact you should start your garden now, because an earlier start means an earlier harvest!

I just lamented that it’s not time yet to start gardening. Then I encouraged you to start your garden?


Here’s the thing: we may not be able to start plants outdoors yet, but we can begin by starting seeds indoors. In this blog post, I’ll show you how to get a head start on the spring growing season by doing just that.

Starting Seeds Indoors for Spring Planting

When to Start Seeds Indoors

Most seed packet labels suggest when to plant based on your growing zone. But in case your seed packet doesn’t – or you’ve lost the packet – here are some general suggestions for a few popular crops.


  • Broccoli, kale, lettuce and other frost-tolerant greens, start seeds six weeks before your final frost date, and transplant seedlings outside four weeks later.
  • Cucumbers, melons, squash, and other hardy fruiting crops, start seeds a couple weeks before your final frost date, and transplant seedling outside four weeks later.
  • Eggplant, peppers, tomatoes, and other frost-sensitive fruiting crops, start seeds about four weeks before your final frost date, and transplant seedlings outside six weeks later.

If you’re not sure when to expect the final frost for your area, try this frost date finder tool.

Tower Garden Tip: With the Vertical Garden Grow Lights Kit, you can garden indoors any time of the year. That means you can start your plants as early as you like and simply move them out once spring arrives. Click here for a blog post about using grow lights on your vertical garden.

5 Things You Need to Start Seeds Indoors

Make sure you have the following tools and supplies to improve your odds of successfully growing strong, healthy seedlings indoors.

1. Quality Seeds

If you want to start your own plants from seed, you’ll first needs seeds. For the best results you should use a high quality seed.

When it comes to sourcing seeds, I’m partial to Territorial Seed Company. They offer organic and heirloom seeds. Two other companies that I recommend are Seeds Now and High Mowing – both offer organic, non-GMO seeds.

Seeds for basil, cucumbers, eggplant, lettuce, peppers and tomatoes ship with every Tower Garden. If you ever want to restock your supply of these same seeds, you can find them here.

Recommended reading: 17 Sources for Seeds and Seedlings

2. Growing Medium

Next, you’ll need something to put our seeds into. Our vertical garden uses rockwool – which helps plant roots efficiently absorb both water and oxygen – and vermiculite as a growing medium.

If you’re using rockwool, it’s a good idea to soak it in pH-balanced (shoot for the 5-6 range) water before planting, as rockwool tends to favor the basic end of the pH scale.  I use water that I have let sit for a couple of days in a bucket to let the chlorine evaporate from it. After 30 minutes of soaking the rockwool, you can plant your seeds.

[Update: I have installed a RV water filter on the garden hose line near my vertical gardens. I no longer have to keep buckets of water for several days to allow the chlorine to evaporate. Click here to read about this.

Wondering how many seeds to plant in each rockwool cube? Generally speaking, the smaller the seed, the more of it you should plant.

When in doubt, reference your seed packets. Instructions for planting are often included on the label.

After planting your seeds, lightly cover them with dry, coarse-grade vermiculite. (This helps keep moisture around the seed, improving germination rates. Seeds also need total darkness to sprout.) Then gently sprinkle a little of the pH balance water you prepared over the vermiculite.

Tower Garden Tip: For Smaller seeds, fill rockwool cube holes only half full with vermiculite.

3. Propagation Container

Seeds – check. Growing medium – check. Now where are you going to plant your freshly planted seeds?

If you order a Tower Garden, it comes with a propagation tray. Which is pretty handy.

But, if you’re startimg your seeds without it, here are a couple of other options:

  • DIY – Most any container that can hold a little water should work. I often use an empty plastic container that originally held salad greens from the grocery store.
  • Buy – If you’re starting lots of seeds at once make a trip to your local hydroponics store. The have propagation trays and plastic dome covers that fit over the top to make a miniature green house. I also use a heat pad under my propagation container which improves germination significantly. The heat pad evaporates water in the tray, and the dome cover holds the moisture in. This creates the humid environment that seeds love.
Starting Seeds Indoors for Spring Planting

4. Water and Nutrients

Is your container of planted rockwool cubes ready? Add less than a half inch of the pH balanced water that your prepared to the tray.

Check your seeds daily and add more water as necessary to ensure the tray doesn’t dry out.  Be sure to use the water that has allowed the chlorine to evaporate.

After my seeds have begun to sprout (which can take a few days to a week or two depending on the plant and propagation conditions – again, reference your seed packet label), you can start to feed them with a 50% diluted Tower Garden Mineral Blend nutrient solution. I add twice the amount of water to the nutrient solution to make my diluted blend.

5. Light

Before your seeds germinate, they don’t need light. So you can put them anywhere convenient. I do my propagating in my greenhouse.

But, as soon as you see sprouts, you should put your plants where they’ll get lot’s of light. In most cases this means using grow lights.

You may be wondering, “I’ve got a sunny window, so do I really need grow lights to start my seedlings?”

Simply check your seedlings, and they will tell you. Most modern windows have UV filters built into the glass blocking the full spectrum light that plants need to thrive.

Either they are rich in color and compact in stature, or they are pale and spindly. If your seedlings look more like the later, they probably aren’t getting enough light.

I recommend fluorescent grow lights. You can purchase a 2 foot grow light at your local hydroponics store or use your Vertical Garden LED Grow Lights if you are starting several trays of seedlings. Your local hydroponics store has the correct color spectrum grow lights for the plant types you are using. If you are growing a flowering bud plant start it will need a red spectrum grow light. Most grow lights are not red spectrum lights.

Here is a photo of a stand my friend Mike DeWayne made from PVC pipe to hold his grow light above his propagating trays.

Starting Seeds Indoors for Spring Planting
Mike DeWayne Photo

Another nice thing about fluorescent lights is that they do not put off much heat, so you can place them as close three inches away from your seedlings. Always keep your lights close to your seedlings, adjusting them as the grow, to keep them growing compactly.

Moving Seedling Outside

When it comes to moving your young seedlings outdoors, a couple of items make the process go a little smoother. The following will protect your plants should you get an unexcited, light frost.

  • Manage the temperature inside your Tower Garden with a submersible heater. Go to your local pet store and purchase an aquarium heater to put in the vertical garden reservoir, click here to see my blog post on its insulation. When set to its lowest setting this should keep your water in the 65 degree range, the perfect temperature for roots.
  • Cover your seedlings with a Weather Protection Blanket to shield them from chilly nights. (Bonus: This UV-resistant blanket can also protect your plants from heat stress in hotter months.)  You can also use row cover material from local nurseries.

How to Harden Off Seedlings

If you’re like me, you’ll eagerly await the day you can transplant your seedlings outdoors. But for best results, you should introduce your plants to the outside world gradually. This is a process called “hardening off.”

When you start seedlings indoors, they know only the stable, safe conditions of your home, where they enjoy consistent temperature, ideal lighting, and protection from pests.

If you pluck them out of that little utopia and stick them into an environment with wind, rain, temperature fluctuations, insects, and so on, they’ll get stressed.

That stress can stunt your seedlings’ growth. In fact, it could even kill them. And clearly, if that happens, your reasons for starting seeds early become rather moot.

So hardening off is important. Fortunately, it’s pretty easy, requiring only a few minutes each day starting one week before transplant day.

Just follow these steps:

  • For seven days, set your seedlings outside in a relatively protected area (e.g., somewhere with indirect sun and little wind exposure).
  • On the first day, leave your seedlings out for only an hour. Then each following day, add an hour and start to expose them to more sunlight.
  • On the final day, your seedlings will have experienced seven hours outside. After that, they should be hardy enough to transplant.

Tower Garden Tip: To start the hardening off process even earlier, aim a small fan—set on low—at your seedlings as they grow indoors, and gently touch their leaves and stems a few times each day.

How to Transplant Seedlings

Once you’ve hardened off your seedlings and they’re about three inches tall with roots growing from the rockwool, you can transplant them. Plant one seedling per growing port in your Tower Garden by gently pressing the rockwool cube in until it touches the base of the net pot.

Vertical Garden Tip: Starting a vertical  garden full of new seedlings? Be sure to use half-strength nutrients for the first month. That formula is: 10 mL of Mineral Blend A + 10 mL of  Mineral Blend B / gallon of water.

In as early as a month, you will be enjoying the first harvest from your vertical garden.

Here is a short video about how to plant your seedlings into your vertical garden.

Your questions and comments are always welcome. Just use the comment box below.

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Other posts of interest:

How to Plant Your Perfect Tower Garden

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