Starting Seeds

This post is a bit early in the year for some folks, but may be just-in-time for others. It will explain how to start seeds indoors, including timing, soil prep, hardware required, etc. It is not exhaustive and I could go into much more details, however, the post is probably too long for most internet browsing people’s attention to begin with. As I may have said before, I will try to be verbose enough to answer questions before they are asked. There are many people that will actually appreciate the details in my blogs.

A tray of cells planted with onion seeds for the 2016 season.

A tray of cells planted with onion seeds for the 2016 season.


So… you (maybe) took my advice and purchased your seeds for 2016. Now what do you do?

It all depends.

Hopefully you put them in a Ziploc bag and placed that in the refrigerator. Just be sure you do not place them against the vent where the cold air comes in or they may get frozen. We’ll go on the pretense that you have your seeds and they are stored away properly.

The next thing to do depends on what your goal is. If you are after simplicity, then wait until one to two weeks after the last average frost date for your area and then plant your seeds in a well prepared garden spot. By well-prepared, I mean an area that has at least 8 hours of sun, does not hold excess water, and has been tilled. If it is heavy clay or mostly sand, you will need to amend the soil with some peat moss, compost, or composted farm manure. Work that in before planting. (I know, permaculture people, you can plant without tilling, but remember I said simplicity at this stage.) The seed packet will give you instructions for planting each type of seed.

A map for frost dates can be found at Cornell to assist you with your planning:

Some seeds really do need to be planted indoors to get a jump on the growing season. And that is the topic of discussion in this blog post. This is especially important for those in northern growing zones that have shorter growing seasons.

The first thing you need to do is determine the timing for planting your seeds indoors. In general, you want to plant seeds indoors 6 weeks before you transplant your seedlings out in the garden. The date you plant them in the garden is determined by your average last frost date. (See link above for New York State) You generally want to transplant your seedlings two weeks after the average last date of frost. In simple terms, plant your seeds indoors 4 weeks before the average last date of frost.

If you plant them indoors to early, they may get leggy and root bound. That will stunt their growth and/or force them into bolting when they are planted.

Not all seeds should be planted indoors and for those seeds that should, the timing is different for certain plants. Here is a non-exhaustive list of seeds that will tell you if they should be planted indoors and if so, when they should be planted relative to the average last date of frost:

  • Lettuce – Plant indoors 6 weeks before the average last day of frost. They also do well direct planted into the garden on the date of the average last day of frost. If the weather is good, a week earlier will be fine.

  • Radishes – Plant outdoors on the date of the average last day of frost.

  • Peas – Plant outdoors as soon as soil can be worked. That means BEFORE the average last date of frost, but AFTER the frost is out and the soil is not saturated.

  • Beans – Plant outdoors one week after the average last date of frost.

  • Corn – Plant outdoors when soil is at the temperature required according to the seed packet. Some corn seeds require different soil temperatures for planting.

  • Tomatoes – Start indoors 4 weeks before the average last day of frost.

  • Peppers – Start indoors 6 weeks before the average last day of frost.

  • Petunias – Start indoors 6 weeks before the average last day of frost.

  • Marigolds - Start indoors 4 weeks before the average last day of frost.

  • Many flowering plants – Start indoors 4 weeks before the average last day of frost.

  • Beets – Plant outdoors on the date of the average last date of frost.

  • Carrots - Plant outdoors on the date of the average last date of frost.

  • Broccoli – Start indoors 4 weeks before the average last day of frost.

  • Cabbage - Start indoors 4 weeks before the average last day of frost.

  • Squash/pumpkin/cucumber – Start indoors on the average last date of frost OR alternatively, plant outdoors two weeks after the average last date of frost. If planted indoors, do not let these plants get larger in their pots before transplanting or they will become stunted. The most you should hold them is two weeks before transplanting. If I plant them in pots, I will leave them on the porch and not even bother germinating them in the house.

  • Kale – Plant outdoors on the date of the average last date of frost.

  • Spinach - Plant outdoors on the date of the average last date of frost.

  • Dill - Plant outdoors on the date of the average last date of frost.

  • Onions Seeds – In New York State, plant indoors mid-January to early February. Transplant outdoors as soon as soil can be worked. That means BEFORE the average last date of frost, but after the frost is out and the soil is not saturated.

  • Onion sets/plants – Plant outdoors as soon as soil can be worked. That means BEFORE the average last date of frost, but after the frost is out and the soil is not saturated.

  • Arugula - Plant outdoors on the date of the average last date of frost.

  • Rutabaga - Plant outdoors on the date of the average last date of frost.

  • Parsnips – I’m still learning the optimum time for this root vegetable because it germinates VERY slowly and then grows very slowly. Last year I planted the seeds directly in the soil at the time of the date of the average last date of frost. I harvested them a few weeks after the first frost of the fall. The root was not very large. This year I will plant them indoors 8 weeks before the average last date of frost and hedge my bets by direct seeding them outdoors as well. I have also switched varieties this year to see if that helps. Remember; some varieties will work for other people, but not in your environment. Don’t be afraid to try new varieties if one does not work out well.

  • Rosemary – Don’t bother planting seeds; it is not worth it. Buy a plant at a nursery or learn how to bring the plant indoors for the winter and then start cuttings for new plants at the end of January. Keeping Rosemary in a continuous cycle is not difficult and will even give you fresh Rosemary through the winter months when it is growing in your house.

  • Basil - Start indoors 4 weeks before the average last day of frost. This will assure you of getting seeds for next year if you want to try your hand at collecting seeds. (And I strongly suggest that you do) Basil can also be direct seeded outdoors two weeks after the average last date of frost; however, the plant may not reach maturity to produce ripened seeds.

  • Herbs (in general) – Start seeds 4 weeks before the average last date of frost.

That should cover the most popular plants. Now let’s get planting our indoor seeds!

Seeds will need a tidy home to grow in, good soil, and plenty of light. Firstly, procure a tray/flat for starting the seeds. There are a few options:

  • 72, 48, or 32 cell plastic tray kits. They will come with an open tray, sections of plastic cells that will go in the tray, and a clear humidity dome. The more cells in the tray, the smaller the cells will be. I use the 72 cell trays because the larger sizes (with less cells) use more soil and the plant does not need the extra root space if planted at the correct time. I can actually plant 288 onion seeds in a 72 cell tray. Each cell gets 4 seeds. Planting 4 seeds per cell is not recommended with other plants. My experience with onions has taught me that I can get away with it with onions. Plastic trays and cells will last for many years. Do not throw them away! I have been using mine for 10 to 15 years. Sometimes a corner of the tray will get a hole. You can put a dab of silicon sealer on it for a fix. What I do is to keep the carrying trays I get at nursery stores when I buy plants. They are heavy duty and are net-like. The planting trays fit perfectly into them and they protect the edges.

  • Peat pots. They will, however, require you to purchase trays to put them in. It is difficult to buy just a tray these days. Most come with plastic cells. (See above)  Furthermore, peat pots are significantly more expensive than using plastic cells and will need to be purchased every year. Peat pots are generally larger than plastic cells and require more soil per plant, and thus, more trays to hold the same amount of plants. From my experience, the peat pot does not help with the roots. In-fact, it makes them root bound most of the time after being planted. I do not recommend these.

  • Peat pellet kits. Many people like these because of the simplicity. They come with a tray, plastic cells and compressed soil plugs that are already in the cells. I do not use peat pellet kits because I mix my own soil. Mixing your own soil is VASTLY less expensive over time, and gives you better control. If you are new to gardening, peat pellet kits may be a good option for you. The trays can be used again the following year and you can decide then if you wish to switch to your own soil mix or not.


The plastic cells and peat pots need soil and the peat pellet kits do not. You can purchase “seed starting” soil in many garden centers and big-box stores. DO NOT buy potting soil for indoor house plants! It is too dense for starting seeds. Also, do not buy coco coir. I tried coco coir last year and was VERY disappointed. It dries out quickly and appeared to not hold nutrients. Do not use garden dirt. It is too heavy and is not sterile enough. You may be able to buy a LARGE bag of seed starting soil from a local garden/farm center that sells farming supplies and feed. I did that for years and it was very economical. This year I did more research and I’m trying my own custom mix of 50/50 peat moss and vermiculite. So far it is doing the best of all soils I have tested. It will be the most cost effective solution, and from what I am seeing, it may be the best medium to use. The down-side will be that you will need to store a big chunk of peat moss and a large bag of vermiculite. That is not a problem for me.

Note: Do not use hydroponic rooting plugs or rockwool for outdoor planting. You could use them, but my experience is that there are much better and less expensive ways to do it. The better ways are explained here.

You have your seeds, you have your trays, and now you have your soil. We need to hydrate the soil and get it into the cells/pots.

If you selected peat plug kits, simply follow the directions that come with it to hydrate them and then plant the seeds according to their instructions. I do not know if they use fertilizer in the pressed peat plugs, so I cannot recommend hydrating with fertilizer water (as seen below) or not. If they provide fertilizer within the plug, then only use water. You can skip the next few paragraphs because it will not pertain to you.

If you selected peat pots, you will need to soak them in plain water until they are saturated.

If you selected plastic cells and they are not new, then you will need to sanitize them. Otherwise they will be contaminated from fungus/mold spores from last year that are still alive on the plastic. Don’t worry, it is easy. Simply soak the used plastic cells in bleach water for 10 to 15 minutes and then rinse off. The ratio of bleach to water is not too particular. About a cup to a kitchen sink of water would be fine. Used flats should also undergo the same sanitization. Do not skip this step for used plastic cells and trays; once the humidity dome is placed on, the little fungus buggers will breed quickly and set your plants back or kill them if you do not sanitize your trays and cells. This is where most gardeners fail and later wonder what happened. Do NOT sanitize peat pots!

Sanitizing used planting cells.

Sanitizing used planting cells.

For peat pots and plastic cells it is now time to prepare the soil. If you mix your own soil, mix it well while it is dry. Put the soil mixture or seed starting medium into a plastic container that will hold enough soil for a complete tray.

Prepare a weak solution of liquid plant fertilizer for indoor plants. This is done by using either granular indoor plant fertilizer or liquid indoor plant fertilizer in some water. Read the instructions for mixing with water, but use only half the recommended dosage of fertilizer for the regular amount of water. Shake after mixing the water and fertilizer together.

Pour the fertilized water into the soil a bit at a time and then mix well with your hands. If you do not like dirt under your fingernails, then wear rubber kitchen gloves. Here is how to tell how much water to use: Squeeze a handful of soil tightly. If you hear the water “squish” between your fingers, but it does not drip out, then it is good. If it drips, then add more dry soil. If it makes no sound, then it is too dry, so add more water.

Pack the soil into the peat pots or the plastic cells. The level is determined by how you will plant your seeds. There are two methods:

  1. Fill to within ¼ inch of the top of the pot/cell. Use this method if you want to place the seeds on the soil and then top it will soil afterwards. If you top with soil after placing down the seeds, be sure to read the seed packets as to how much soil to use. Some seeds are VERY tiny and may not be able to push through ¼” of soil.

  2. Fill to the top of the pot/cell. Poke hole(s) into the soil and place the seed in the hole. Push the surrounding soil into the hole to seal it over.

When I say to “pack” the soil into the pots/cells, I do not mean to pack it hard. You want the soil to be tight enough so if you water from the top, the soil does not wash down. If you pack it too tight, it will be more difficult for the roots to grow through. I made myself a wooden packer from a junk piece of wood that I trimmed to the shape of the cell. It allows me to pack quickly. That is important if you are doing hundreds of cells.

Bin of mixed and wetted seed starting soil with packing wood block and filled cells.

Bin of mixed and wetted seed starting soil with packing wood block and filled cells.

When planting the seeds, you can either plant one seed per cell/pot or plant multiple seeds per cell/pot. Do not use the same hole for multiple seeds if you go that way. Space the seeds apart. I generally plant two seeds per cell because I have a lot of my own seeds and can spare them. My goal is to be sure every cell has a seedling. Not every seed will germinate. If you have limited seeds and want the maximum amount of plants from them, then only plant one seed per cell/pot.

Once the seeds are planted you can place the clear plastic dome on. It is not necessary, but if you do not plan to mist the trays with water then the dome is helpful. You can also cover the top with plastic wrap until you see the first seedling germinate. You DO NOT want the top of the soil to dry out during germination. With that being said, you also DO NOT want to saturate the soil. It should look damp, but not really wet.

The dome can be left on for two days after the seeds begin to germinate. Remove it after this time or you will risk damping-off fungus. That is where the seedling begins to grow, the stem withers, and then the seedling topples over dead. If you sanitized correctly, you will have less of this problem. Some plants are more sensitive to this than others. Furthermore, if you did not use good potting soil (not sterile) then you will see more of this problem.

Most instructions tell you to put the seed trays in a dark location until the seeds germinate. I am going to tell you that is non-sense. Plants want light as soon as they pop out of the soil because they need to begin photosynthesis immediately. The sooner the plants have good light, the stronger they will grow. With that being said, placing them in direct sunlight for several hours with a dome in place may create a greenhouse effect and heat the soil too much. Be sensible and check to be sure that inside the dome is not hot. That generally is not much of a problem when starting seeds in late winter.

Try to keep your seed trays warm at 70-75 degrees. However, I do not use heat mats and mine do fine. If you are a perfectionist, you can buy heat mats. I heard that they do not last for many years, though. Room temperature will work fine. If you place your trays next to a window for light during the day and it is drafty, I would move it away from the window until the plants have their second leaves. Some people put their trays on top of their refrigerator for some heat. The heat rising from the back of the refrigerators rises upwards.

The next subject is light. Seedlings require a lot of light. A south facing window will suffice. Otherwise, consider purchasing a grow light. You can buy florescent grow lights inexpensively at the big box stores or you could get a regular florescent light at a big box store. If you purchase a florescent light, be sure to get it with a “cool” temperature light spectrum.  A 6500k florescent light tube will do best. Do not buy LED shop lights. Their color spectrum is too narrow.

In regards to florescent lights, you can get T12, T8, T5, and T5 HO fixtures. The best are the T5 HO fixtures, but it is difficult to get the correct tubes for plants unless you order them through the internet. Therefore, the T8 fixtures might be the next best thing. Generally you can get them in stores like Home Depot or Lowes. Walmart does not carry many florescent tubes or fixtures, but they do carry grow lights. Their T8 grow lights are not very strong and will require two per flat. At $11 each, that is not too bad. Stay away from their new T5 HO grow light. It is a hazard and could cause a fire or a broken tube. It is cheap beyond use. Furthermore, it has a metal housing, but only has a two prong plug. That could be an electrical hazard around water.

Once the seedlings are growing, be sure to keep them watered with fertilized water. Use the half strength water for two weeks and then possibly switch to full strength. Let the plants tell you when they need more nutrients. They will generally yellow and possibly show green veins with yellow in-between when they are deficient. The top of the soil should begin to dry out slightly, but not completely, before watering again. You can water three different ways:

  1. Fill the tray with ¼ inch of fertilized water and let it be. That is generally enough for the plants unless they are larger and outside. This is what I do mostly when they are still in the house.

  2. Fill the tray with ½ inch of fertilized water, wait 30 minutes, and then pour out the excess water. This works well when the plants are getting larger and using more water. When I put my plants on the porch to harden them I use this method because it is easy to dump the overage outside.

  3. Water from the top. This is the least recommended way because the water pattern is irregular and some plants may not get enough water. I only do this if I am in a hurry and I see that they need water quickly.

Onion seedlings! It really is worth the little bit of work to get them started.

Onion seedlings! It really is worth the little bit of work to get them started.


About a week before the plants are to be transplanted outdoors, you will need to “harden” them off. That means we need to get our indoor plants acclimate to being outside without shocking them. We can do that by putting them in a shaded area that only gets one or two hours of morning sun for the first two days. If the nights get cold, be sure to bring them indoors. Some seedlings are a bit sensitive to the cold until they are hardened. The exceptions are onions and possibly leeks. (I’m new to leeks this year) Increase their sun exposure each day for up to a week. By the end of one week, they can be out in full sun. If the weather turns bad, you can extend the time period for two weeks. However, if you wait longer, your plants will become root bound.

To transplant do the following:

  1. Overwater your plants and let them set in the water for a half hour. You want them saturated in their cells/pot.

  2. Be sure that the garden area is ready. It should have loose soil that is not clumpy or saturated.

  3. Stake out a row with two sticks and some string or fishing line.

  4. Work a little 10-10-10 fertilizer into the soil along the string line. (for tomatoes, you may want a 5-10-10 or none at all until they begin to develop fruit)

  5. Bring the plants out to the garden. Dig a hole, pour water into the hole, and then put the plant into the hole so the garden soil line will be slightly higher than the top of the plant's soil. Fill the hole with garden soil so it covers the plant’s potting soil. I often will bury the plant up to its first set of leaves. It is okay for the hole to be muddy unless the soil in the garden is very wet. If it is very wet, then skip watering the hole. DO NOT LEAVE THE PLANT OUT OF ITS CELL/POT! Some people will pull the plants out and lay them down on the ground to “plan” how they will look. Do not do this! The roots are VERY sensitive to air and sun at this point. You will set them back for a week or permanently if you do this. Furthermore, it is always best to transplant on a cloudy day. A hot day in full sun is the worst, but if done correctly will be fine.

  6. Water the plants after you are done planting them. Be sure they do not dry out; the first couple of days are critical. If you see them wilting, give them more water. With that being said, do not make it muddy with too much water. Within a few days they will “take” and will look perky.

I wrote a lot of instructions because most new gardeners have a lot of questions and I tried to answer them beforehand. Planting seeds is VERY easy and enjoyable. And the best part is the anticipation of the germinating seedlings. You may find yourself looking at them several times a day to check on their progress. That is a good thing. Anything to get people off the couch or away from their electronic devices is a good thing.

Presently, my onions and leeks have germinated already. Yes, it is the end of January and my garden is already on its way. Growing plants is a real comfort to our spirits.

I also have some apple seedlings that are growing. That is a special project just for my mental health. The seeds came from my own apples. Generally speaking, apple seeds will not produce an apple tree with really good apples. They will NEVER have apples like the parent plants. There are just too many genes in a state of heterozygosity for that to happen. It is like rolling the dice. One in a thousand will be a great apple tree. I’m in! I find things like that to be exciting. In 7 years I will tell you how they taste.

(Actually, because I have an orchard with only good apple trees, my odds are slightly better and a LOT better than using seeds from store bought apples.)

These three seedlings began life in a damp paper towel in a Ziploc bag beginning in the fall of 2015.

These three seedlings began life in a damp paper towel in a Ziploc bag beginning in the fall of 2015.

I wish you well in your gardening!

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