My 2021 Spring Garden Seed Starting Plan

Getting ready to plant a garden can be an overwhelming task, especially when a lot of your seed packets come with instructions to start indoors a certain number of weeks before the last spring frost. I put together a little guide for how I am learning how to handle seed starting, since I’m starting a new growing season with a greenhouse for the first time! I am by no means an expert in the area, but it’s always helpful to get tips and tricks from others when starting out, so I thought I’d share my info!

Round 1 is complete!

1: When to start seeds

When to start your seeds varies depending on seed type. Usually the envelopes that your seeds come in give you starting recommendations, but if for some reason it does not, you can always Google that information! I’ve definitely had to do that myself this year. The general range for seed starting can be between 2-12 weeks before last spring frost. A few types of seeds require starting 2-3 months in advance, such as artichoke and celery seeds! Others suggest that you sow your seeds directly into its permanent location in the ground. Sometimes this is because the plant is susceptible to transplant shock.

2: Choose your seed starting soil

There are lots of pre-made seed starting soil mixes on the market, but they are not all created equal. Each one has a different ratio of materials, but they all have one major thing in common: they are not mainly composed of actual soil! Pretty surprising considering it’s called soil, but it’s actually a combination of other materials that allow the seed the air and moisture necessary to germinate. Germination occurs when the tiny seedling begins to emerge from the seed, and in the course of that process the new plant has no need for the nutrients contained in soil. Within a seed is a structure called an endosperm, and it provides the nourishment necessary for the seedling. As a result, plants cannot be sustained in their seed starting mix for the long-haul. Eventually that endosperm runs out of nutrients and the plant must begin relying on its environment for nutrients. 

Last year I bought a block of expanding seed starting mix because it was easy and cheap, but I was not impressed with the results. To be fair, however, I did probably leave my seedlings in their starting mix far longer than they should have been left, but the more I’ve learned from research and watching others, the more I saw the flaws in that mix. I believe that what I used was 100% coir coconut fiber, and it lacks the variety that an actual mix would provide. This year, I am trying the following recipe:

  • 1-2 part(s) peat moss/coir coconut fiber
  • 1 part perlite 
  • 1 part vermiculite 
  • A little compost if using a soil blocker to help the soil hold together

When I mixed mine up I really based the amounts of coir and composed on look and feel of the soil. You want it to pack together somewhat, especially if you’re making soil blocks, so you have room to play with the proportions.

This mix is a combination of a few recipes I have found online that I modified to fit my needs. The original mix I started with did not include compost, but I feel like a little is necessary to help keep the mix held together with my soil blocker. More on that in a minute.

Everyone has different preferences when it comes to seed starting mix, but the major takeaway from my research on it is that drainage is crucial to the mix. If seeds don’t have light and airy soil, they will have a harder time germinating.

3. What to plant your seeds in

If you go to the store and buy a seed starting kit, you’re probably going to find yourself buying a plastic container of little cells with a lid. This can be a fantastic place to start, but there are other options out there besides the (usually overpriced) premade options. 

There are also many size options with the plastic cells. Larger seedlings may need larger cells to germinate and harden off. If you regularly buy the small cells of flowers at nurseries and garden departments, save those cells and reuse them!

The issue that can arise with using plastic cells for seed starting is that oftentimes those cells get damaged as you remove the seedlings and they become single-use. This causes you to have to buy new every year or so, as well as adding to the unfortunate amount of plastic in our landfills. I’m not anti-plastic by any means – my garden is currently covered in plastic! – but I do like to reduce my use of it when it is convenient. 

Another option that is also more ecofriendly, if you’re looking for that, is using biodegradable peat moss cups. I love a good peat moss cup because you can just stick the whole thing in the ground when it comes time to plant and it will decompose as the seedling grows. However, if you want to do this, there are a few things to consider from my experience. 

  1. Don’t buy cheap. I found a big pack of them on Amazon last spring for really cheap and they were not good quality cups. While they may decompose eventually, they do not do so fast. They also would not drain water AT ALL. I had to punch holes in the bottoms to get the soil to drain…definitely not what you want with delicate little seedlings trying to survive. 
  2. If you get a good brand, the decomposition process does happen quickly depending on how much you water. I’ve gone to pick up a pot and a piece of it break off in my hand. This is a sign of a good brand cup, but they also require more delicate handling. 

The newest option I’ve been introduced to this past year, and the option I am trying out, is using a soil blocker. A soil blocker is basically a soil mold that will create little cubes of your soil mix with a small indentation in the top for your seed to be placed in. I bought mine off Amazon, but I’m sure you can find them in garden supply stores as well. Mandi over at Wild Oak Farms uses a soil blocker and was who I got the idea from, and she doesn’t have any issues with the mold not holding its shape. This is why I am adding compost to my mix – I’m afraid the coir, vermiculite, and perlite won’t hold together well on their own.

I started my first round of seed starting this past weekend and used my soil blocker for the first time. The biggest thing I saw is that packing your soil into the cells tightly is the key to a good little block of soil. If I shoveled the cells full of soil first and then packed it down, I had soil blocks that fell apart easily. If I went in stages and added a little soil, packed down, then added more, packed, etc., I was able to get a much better block of soil. Because of my large amount of vermiculite and perlite, I’m going to be very careful about how I water my seedlings. That much aeration is great for those little seeds but not so great for keeping a mold together!

The reason I love the idea of soil blocking is that you don’t have to worry about having enough pots or cells, you aren’t wasting any plastic, there’s no worry over whether your soil is draining, and the only supplies you have to replenish each year is the soil. I also bought a stack of plastic trays for the soil blocks to sit in so they are easier to transport and if they do break down, they will still be contained. 

4. How to care for seedlings

I think one of the most intimidating aspects of indoor seed starting for me is what to do once the seeds have germinated. You’ve got these tiny, delicate little plants that you now have to keep alive. Again, I am no expert in this field, but from what I’ve researched there are 3 major factors to keep in mind when caring for seedlings:

  • Water 

Water your seedlings gingerly. Don’t use a watering can that you normally water full-blown trees with or you may beat the poor things into the soil. Sometimes using a water hose nozzle with a mist setting is a great way to water delicate seedlings. Some seedlings are strong enough to handle it, but I killed several seedlings last spring with my watering technique. Even the mist setting on my hose pummeled them into the dirt. In my defense, they were poppy seeds and you really should only direct-sow poppies, but I digress. 

  • Temperature 

This is the one that concerns me the most personally. says the temperature needs to be no higher than 80 and now lower than 50 while seeds are germinating. If you’re starting your seeds inside your home, that’s no big deal. If you are starting in a greenhouse like I am, it requires some planning and attentiveness unless you’ve got a climate controlled greenhouse. The better insulated your greenhouse is, the less of a concern this is for your seedlings. 

  • Sunlight

Lots of light is vital for healthy seedlings. Light requirements for germination vary depending upon the type of seed, but once those little plants start growing they need plenty of light to get going. Grow lights are great options for indoor seed starting, winter seed starting, etc. We initially believed that our greenhouse would have adequate sunlight, but we think that at this point in the year a grow light will be a lot of help.

5. What does it mean to “harden off” your seedlings?

Hardening off seedlings is really just another term for letting your seedlings get acclimated to the outside environment. Burpee has a great article on how to harden off your seedlings once it’s time to move everyone out to their respective garden spaces ( The basic idea is to gradually introduce the plants to the outside environment by bringing them out for a short period of time and slowly adding more outdoor time, sometimes hour by hour, each day until they are outside 24/7. Be mindful of their needs for water during this time, because whether they were in a greenhouse or a sunny spot in your house they are not getting 100% unfiltered sunlight and can be susceptible to sunburn and dehydration. It’s a lot like us – if we spend the whole day in the sun the first hot day after months of cold, gloomy weather, we will burn and be more prone to dehydration because our bodies are not yet acclimated to the climate change that occurred as the seasons shifted. 

So there it is! My not-so-professional guide to seed starting. I hope it was helpful to someone! Feel free to ask me anything or make suggestions. Gardening is a lifelong learning process, and I personally love to learn more about it!

2 thoughts on “My 2021 Spring Garden Seed Starting Plan

  1. For me, the biggest factor for successful seedlings is LIGHT, not water or temperature (although of course freezing temps are disastrous for most seedlings and over or under watering does cause problems.) Best of luck in the coming season with your new babies.

    Liked by 1 person

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