Flower Farmer's Study Club Part 1: Seed Starting

This is one of a series of posts that are aimed to help new growers understand the basics of growing. The information is comprehensive and will help you understand how to grow - even if you’ve never grown anything or gardened or farmed before!

One of the most important and most basic skills a flower farmer can have is seed starting. As I’ve mentioned before, seed starting is the way that a flower farmer can economically and effectively obtain the quantity and variety of plants required for creating the volume and diversity of material to sell.

While it seems rather intuitive, seed starting can be a bit tricky depending on the species so I wanted to cover a couple basic concepts that are important to keep in mind when starting seeds.

Germination Basics

Germination (a fancy term for what happens when your seed starts to sprout) is an almost mystical process. You take this hard, brown, dry seed that looks more like a rock or pebble or grain of sand than anything living that suddenly explodes into a living real life plant.

How does this happen?

Seeds are dormant plants just waiting to start to grow - inside every single seed there is a plant embryo that is asleep, just waiting for the right conditions to be met in order to start growing. Once those conditions are met, you’ll see a little sprout start to form - that’s usually the tail end of the root - and that’s the sign that your seed is starting to grow!

Generally speaking there are three things that trigger the germination of a seed

1) Water

2) Heat

3) Light

That’s it.

It’s pretty simple, but by providing these three things, the majority of seeds will go on to germinate and grow into plants.

You’re basically telling the seed that it is time to start growing, since the combination of water, heat and light signals that the growing season is starting.

You can have a lot of water and light (such as during the winter with snowpack or rain) but if it isn’t warm enough, the seed won’t sprout. Alternatively, you can have a warm and bright summer but if there isn’t water to soak the seeds, they won’t germinate either.

Seeds have this built-in mechanism to prevent them from sprouting randomly during times when it wouldn’t be conducive to growing a plant. Yes, the mechanism isn’t perfect, but it works the majority of the time.

There are exceptions to this ofcourse. Light isn’t always needed as a trigger - violas, bupleurum, and Chinese forget-me-nots are three examples of plants that actually need the absence of light in order to germinate, but they are more of the exception than the rule.

Some seeds aren’t easy to germinate

There are some seeds such as cress, zinnias, sunflowers and marigolds that are very easy to germinate. You can toss them into some moist ground and they will take off very quickly.

Not all flowers or plants are the case with this. Fancy rudbeckias like ‘Sahara’ and ‘Chim-Chiminee’ have lower germination rates for me as well as trickier perennials like Jerusalem Sage (Phlomis tuberosa) and Bugbane (Cimicifuga).

On your packet, there usually a statistic known as a germination rate that comes as a percentage. For instance, on a zinnia packet it will say something like “98% germination rate” that comes from the seed company testing out seed to determine the percentage of seeds that germinate.

You can test the germination rate if you’re having problems starting a seed very easily - and you don’t even need to get any soil!

1) Simply take a paper towel, place some seeds into it, moisten the paper towel (you want it slightly damp, not sopping wet) and place it in a plastic bag

2) Set that plastic bag in a warm area and then check every couple of days to see how many seeds have germinated

3) Once you have a final tally (around a week or so for most seeds) divide the number of seeds that germinated by the total number of seeds - that will give you your germination rate.

You can try it on 100 seeds if they are small and economical to do so, or you can try with 10 seeds (which is easier to count and handle)

Cold Stratification

There are some seeds - mainly perennials - that will have really sucky germination rates, hovering around the 10-20% germination rate.

You may get frustrated that they never seem to sprout, even if you wait several weeks, and most people end up giving up on these seeds.

What’s going on? Did you get a batch of bad seeds? Do you have a “black thumb”?

Chances are that you don’t - it’s usually the case that low or no germination rates on seeds, especially perennials are because the seeds need something else to trigger their germination.

Perennials generally want to ensure that they are growing in the spring after a winter. They definitely don’t want to start sprouting in the fall during those days or weeks where it starts getting a bit warmer and almost feels like summer again - that won’t allow the perennial to get established before the winter.

Instead, perennial seeds have a built-in mechanism to sense when they’ve gone through winter, and they won’t sprout until that mechanism has been tripped.

The way to trip that mechanism is to chill the seeds in a moist environment for a certain period of time - anywhere from 30-90 days. This would be obtained out in nature by the seed lying dormant on the ground and being covered by snow and ice and rain for a good length of time during the winter season.

You can do that - throwing the seeds out into the wild and letting mother nature chill them, and it works well for some species like larkspur, or occurs naturally if you have plants that are reseeding such as rudbeckia and echinacea.

On the other hand if you’re a control freak like myself and want to ensure that you can keep track of your seeds, you can perform cold stratification through one of two ways: outdoors in containers, or indoors in the refrigerator.

If I’m sowing a lot of seeds that I want to be ready in the spring, I’ll sow them outdoors - but into containers I’ll do this at the end of the season once frost hits to get them ready for the winter chill, sowing them into sturdy pots or cell trays in order to allow them a good place to grow into. I’ll keep them moist during the fall and then during the winter let the snow and ice pile on top of them (the more the merrier!) and then wait for germination in the spring.

This method I actually learned from the gardening phenomenon known as “wintersowing” - made famous on Gardenweb back in the early 2000’s that involved planting seeds into milk jugs to create mini-greenhouses for seeds to cold stratify themselves. The concept is the same, but I don’t drink enough milk to generate enough jugs for the plants I want to grow, so quart pots it is!

A word of warning - I don’t sow into small cell trays (like 128’s) because I find they tend to dry out too quickly. A 4” pot is actually pretty perfect for sowing a large amount of seeds that I can then divide out into individual plants later on.

If you’re really wanting to do things the right way, you can also wrap the seeds in moist paper towels (or coffee filters) place them into a plastic bag (similar to what you would have done for the germination percentage exercise) and then place the into your refrigerator (NOT THE FREEZER) for the set amount of time. We’ll write on the bag the name of the species (ECHINACEA PARADOXA) and the number of days needed for cold stratification (90 DAYS) and the date when they should come out.

This is a great method to use if you’re trying to start seeds during the growing season when ambient temperatures outside are not cold enough to stimulate the germination. That way you can simulate a “winter” in April, May, and June and then get your perennials going fast and strong for a good fall planting.

Direct Sowing

Direct sowing is exactly what it sounds like - sowing your seeds directly into the ground.

This is the way that most people think about growing seeds, sprinkling them onto the ground and letting nature take of the rest.

It’s not quite that easy, but the concept is the same - placing the seeds directly into the area you want to grow them is a quick and easy and efficient way to skip the whole work of growing out seedlings. We generally only use them for growing out quick growing species with big seeds - ornamental grasses, zinnias, sunflowers, calendula and marigolds to name a few.

Advantages

Easy - you just sprinkle seed onto the ground
No extra setup or equipment - no dealing with trays, lights, humidity domes etc.
No transplanting needed
No hardening off required
Direct sown seedlings many times are much stronger and vigorous than transplanted seedlings

Disadvantages

Lower germination rate most of the time due to extenuating factors
Seeds can be eaten by animals, washed away, blown away in the wind, buried under soil, outcompeted by weeds
Less control over germination environment - have to deal with weather and precipitation
Difficult many times to maintain enough moisture to achieve germination
Hard to direct sow fine seed like foxglove and poppies

Seed Starting Containers

There are many containers you can start seeds into. I’ve seen everything used from soil blocks to toilet paper tubes to newspaper pots to coco coir pellets, and all of these you can have good success with.

However if you’re looking to grow a large quantity of plants, you’re going to be left with three options really - soil blocks, cell trays or pots.

Soil Blocks

Soil blocks are these handy-dandy compressed pellets of soil that come out of these little hand-held presses. Similar to the coco or peat pellets that you can start seeds into, the compressed blocks are a very eco-friendly option. You can place a seed onto the top of this cube of soil, and they will grow into some pretty fantastic little plants.

Advantages

Great for starting a lot of seedlings in a small amount of space, especially under shop lights
Great root development - natural air-pruning occurs on the outside of the soil blocks
Quick growth and quicker to transplant than planting into flats
Reduced plastic waste - only the trays or flats are usually plastic, which can be reused over and over
Easy transplanting - you just pick the block up and transplant

Disadvantages

Can dry out very quickly - can be too hard to keep up with watering when the weather gets hot
Takes more effort and time to make soil blocks than it does to fill a flat
Cannot be overhead watered - must be bottom watered, which can lead to uneven water distribution and takes longer
Soil blocks can start crumbling before the roots can fill it, which can make growing them out difficult
Tend to develop algae much quicker for us than cell trays
Will not survive being knocked over or knocked off a bench - you’ll be left with a tangled mass of roots, stems, leaves and soil!

We tend to use soil blocking when we’re growing hardy annuals and perennials in the wintertime. Growing space is at a premium, and soil blocks allow us to cram a lot of plants into a very small growing space under lights.

It’s not bad when you just have a couple flats that you’re growing out - but when you start getting dozens and dozens of flats of soil blocks, it gets much more difficult to keep up with watering and transplanting. And when the weather gets warmer, tiny soil blocks dry out very quickly to the point where we have to water the seedlings two, three times a day.

Cell Trays

Cell trays (otherwise known as flats) are the little plastic doodads with multiple little cells that you can grow plants in. If you’ve ever bought a six-pack of plants at a nursery, then you already know the type of container I’m talking about.

Cell trays are the way a lot of flower farmers grow their seedlings. It’s been the way plants have been grown in the industry for decades, and its the one that all the major suppliers of perennials, annuals and houseplants all use.

Advantages

Easy and quick to fill - you can have one filled in a matter of seconds, smoothing off and tamping down the soil into the cells
Cell trays transport very well, holding plants in place even when flipped upside down or shaken or knocked off benches
Easy to water - either overhead or bottom watering
Hold up well in the weather, even in the winter
Encourage good root system development
Works well with vacuum seeding systems - which can be a gamechanger depending on your setup and volume!

Disadvantages

More plastic waste
Bulky to store
Can break or melt in full sun, especially the cheaper/thinner cell trays
Need to be washed out between seeding (and can be a major pain to do so)
Difficult to extract seedlings - may require a chopstick or dowel to push out seedlings from the bottom
Can be difficult to grow good root systems sometimes if the cells aren’t draining properly ( can cause waterlogging)

Pots

Although we don’t use pots too frequently - most plants we prefer to grow out as small seedlings before transplanting since the smaller plants usually adapt more readily and quickly to the environment - there are occasions in which we will start plants in pots. As previously mentioned, we sometimes use pots to start large amounts of wintersowing perennials and annuals - the pots stay moister much longer than cell trays or soil blocks and are easier to handle and allow for a larger root system to form.

Advantages

Quick to fill - usually you have less pots than cell trays or soil blocks
Good for species that take a long time to germinate like phlomis - the soil stays moist and is less vulnerable to drying out and requires less watering
Excellent for seeds that are best sown as a clump such as ornamental grasses or large pots of quick growing annuals like gypsophila or cress
Great for winter stratification of seeds - allows you to keep all the seeds contained in one pot

Disadvantages

Pots are generally more expensive and take more potting mix to fill - may not be economically feasible for growing out a lot of seedlings
Generally don’t come with flats, so each pot has to be moved around individually
May be more prone to waterlogging and developing algae or fungus due to larger volume of soil and increased moisture retention
Take up a lot of space for the seedlings you get in return

Equipment for Seed Starting

Heat Mats

Heat mats are electronic devices that are used to warm up the soil. Warm soil is a great thing to have because it helps with more uniform germination, helps seeds start to sprout more quickly, and then helps those seedlings to grow more robustly after they sprout.

Heat mats keep the soil between 60-85 F, which are the perfect temperatures for most seeds to start sprouting. There are more expensive heat mats that can have more control over the temperature, but generally speaking even the cheaper heat mats will keep the seeds warm enough to start germinating well.

If you are doing a lot of seed starting, you may want to look into a germination chamber - essentially a large box or enclosure that keeps the air and soil moist and warm - that will help to grow seeds quickly and uniformly and give you excellent germination of thousands of seeds.

If you don’t have a heat mat, that’s still OK - seeds will do well with a warmer ambient temperature even if its not right on the soil - but know that your seeds may sprout and grow on a little bit slower.

You also will want to turn off the heat mat after your seeds sprout - especially if they are hardy annuals that actually do better with cooler temperatures like sweet peas and gypsophila so they don’t get super leggy.

Humidity Domes

Another useful item for seed starting are humidity domes.

The clear, plastic domes that go over seedling trays, they are very important for starting seeds.

Remember that we need water (or moisture) as one of the three triggers for germination? Humidity domes play that very important role of keeping up the general humidity of the seeds.

This plastic dome goes over the top of the tray and increases humidity to 99% which allows for the seeds to rest in a nice and moist environment that is consistently at the same humidity and moisture level. Seeds love this, and will start growing very vigorously when popped into a nice and humid environment.

It makes it much easier to keep your seedlings watered - taking off the humidity domes, most seedlings wilt within a day or two while the humidity domes keep plants moist and perky for weeks on end while they’re growing.

Artificial Lighting

Sunlight is the best light of course - it’s natural, it’s powerful and doesn’t require you to plug it in or set it on a timer - but in order to use sunlight you usually have to either have a heated greenhouse in winter or start your seeds outdoors during the growing season.

If you’re not using the sun, don’t worry! There is another option - you can use artificial lights to stimulate the sun.

What kind of lights do I use?

The lights don’t have to be the special grow-lights with red and blue and purple LED’s that you generally see - I think that those LED lights are gimmicky more than anything else - you can use the regular shoplights that are used to light garages, barns, sheds and utility rooms all over America. The simple T5 light bulbs will work just fine to grow just about anything as far as seedlings go.

It doesn’t even really matter as far as what type of light bulb you use either. Cool, warm, daylight, plant, bathroom - it doesn’t matter so long as it is producing a good amount of light.

What kind of bulbs are best for seed starting?

Yes, you can get into the specifics of wavelengths of light being optimal for plants - but for the purposes of growing seedlings most colors of light will work just fine so long as the output (lumens or luxe) is high enough.

I prefer to choose light bulbs that are pleasant to look at, so avoid the reds and blues and purples - going with a standard daylight bulb (6500K) .

A single shoplight that holds two T5 light bulbs will grow a lot of seedlings, especially if you’re able to cram them into soil blocks and cell trays.

Keep your lights close to your seedlings

You don’t want your lights to be more than 6” away from the top of your soil. In fact, the closer the better - the light intensity drops off exponentially the further that you move the object away from the light source.

If you keep your lights far away from your seedlings, they’re going to try and stretch to reach the light- and that’s when you get long, floppy, thin, fragile stems that are easily broken in the wind or when moving them around.

We like to keep our lights really close to our seedlings - 3-4” inches, and we let them grow as close to the lights as possible - this creates nice short, stocky, healthy seedlings that will grow on to create nice healthy and solid plants.

Do I have to keep my lights on a cycle?

You can - but to be honest, I usually just skip the timers on lights.

I’ve been growing plants under lights for years, and I’ve experimented with keeping them on and keeping them off. I’ve never seen much of a difference as far as plant growth and productivity, so we just make it simple by keeping the lights on 24/7 for seedlings.

SELF TEST

What is germination? What are the the three triggers that start germination?

Can you name a flower that doesn’t require one of the three triggers for germination?
What is a germination percentage? How can you test germination percentage for your seeds?
What is cold stratification? What type of flowers need cold stratification?

Name two ways that you can provide cold stratification for your seeds
What is direct sowing?

Name one advantage of direct sowing for a flower farmer

Name one disadvantage of direct sowing for a flower farmer
What are soil blocks?

Name one advantage of soil blocks for a flower farmer

Name one disadvantage of soil blocks for a flower farmer

What are cell trays?

Name one advantage of cell trays for a flower farmer

Name one disadvantage of cell trays for a flower farmer

What are heat mats? How can they be helpful in seed starting?

What are humidity domes? How can they be helpful in seed starting?

What kind of lights can you use for seed starting? Do you have to use special “growing/plant” lights for seed starting?

BONUS: How can you provide cold stratification for seeds during the months of June, July and August? Explain below

WriterNovember 7, 2019