Home Gardener’s Quick Start Guide to Starting Seeds in Soil Blocks

Step 1:

Gather supplies: labels, pens, seed dishes, and toothpicks. I use a lab labeling system to keep all my supplies organized and to make the process faster when I have multiple trays to label. The lab tape I use is oil, acid, and water-resistant and can withstand extreme temperatures. Ultimately, this means it will not wash off the tray no matter what I do to it. Despite its toughness, when you purposefully remove the tape it lifts magically leaving no sticky residue. Painter's tape is pretty much the same stuff and can be used the same way (but I do find lab tape sticks better). I always use a designated garden pen since they are light, water, and fade-resistant. I made the mistake of using a sharpie one year and unfortunately found out they are not fade-resistant. I also use two ceramic condiment dishes, one for water and one for seeds along with a toothpick to pick up those tiny little rascals.

Step 2:

Put on a good podcast. Admittedly seeding trays takes a bit of time and patience. There are newer soil blocking systems out there to speed up the process for commercial growers which I have and love (you can find them here), but I find the process of seeding rather meditative, especially when I have on a good podcast or some music.

Step 3:

I dip the tip of the toothpick into the water and then pick up a seed. Avoid using plastic dishes since they hold static electricity and you will end up chasing the seed all around while it deftly outmaneuvers you.

Step 4:

To cover or not to cover. If the seed requires light to germinate, I place the seed in the divot at the top of the soil block and firm it into place (good seed-to-soil contact is important for rooting). If the seed requires darkness, I ever so slightly push it into the soil block with the toothpick and then cover the top of the soil blocks with vermiculite. Usually, the seed pack will indicate what the seed requires.

Step 1:

Maintain moisture. It is important during the germination process not to let the blocks dry out too much. They should be damp to the touch. I don’t mess with humidity domes and have never experienced poor germination. If you are just waiting for germination, you can mist the blocks with a misting bottle, but I find it most efficient just to pour a bit of water in the tray for them to soak up and pour off any excess. I have read some say that doing it that way can cause seed rot/fungus but I have not encountered this.

A little note here on "dampening off". "Dampening off" is a disease caused by a fungus or bacteria that cause the seedling to not germinate or abort after sprouting. It is called "dampening off" because the bacteria and fungus that cause the disease thrive in cool and wet conditions. To avoid this happening make sure you are using a good quality potting medium and not garden soil, keep the soil temperature within germination range by using a heating mat during germination, and clean all your trays and seeding utensils thoroughly. Please see the resources at the end for more information.

Step 2:

Give them the proper temperature and bottom heat with a designated germination heat mat. Seed packets will usually tell you the ideal temperature range for that seed to germinate. Some flower seeds are not as picky and will generally germinate at a wide range of temperatures, but some I have found are very picky and need precisely what the pack says without a degree change in either direction. For these cases, I use a temperature probe that I gently insert between the soil blocks. Some temperature probes just monitor the temperature and that is all, while others allow you to plug your heating mat into them and set a range of temps. This causes the heat mat to turn on and off based on the range you have set. I have noticed that when I do not use bottom heat I generally do not end up with uniform germination. In this picture, you can see the ambient temperature in the garage is 58.8 while the soil temp of the blocks is 68.3 due to the heating mat.

Step 3:

Watch closely for signs of germination and once 50% or greater have germinated move them under the lights. Any fluorescent/LED shop lights will do if you are just starting seeds and plan to move them out to the garden, but if you plan to grow to the point of flowering/ fruiting then you will need to have full spectrum lights. You can go down a rabbit hole when researching lights for seedlings. I can only speak from my experience, but I have found that the standard LED’s from the local big box store do the trick (almost) as well as my more expensive “grow lights”. What will NOT work is putting them in front of a window, doing this leads to leggy seedlings that are using up all of their energy bending & stretching to find the sun. One important thing to note is that the light source needs to be incredibly close to the seedlings (like 2 inches close). I was stunned at this, but the fact is that the lights we use are nowhere near the strength of the sun and dissipate quickly the further away they are placed. To avoid stretched & leggy seedlings it's important to place them very close to the light source and move this light source up as the plants grow taller. The other thing to note here is "day length". Plants need periods of daylight and darkness to develop properly, but again because artificial lights are not as strong as the sun, they need a little extra "daylight" time. A pretty good rule of thumb is 16 hours of daylight under artificial light. I find it super helpful to use a cheap timer that turns my lights on and off since I'm just too prone to forget.

Step 1:

As discussed in the previous section proper lighting is important to prevent weak seedlings. Continue to move the light up with a pulley (see picture) as the seedlings grow to keep the light about 2 inches above the canopy (see picture).

Step 2:

As the plants grow, they will need to be watered (usually) daily. I do this by pouring water into the bottom of the tray and leaving it for a few minutes (see picture). Whatever excess is not absorbed I pour off the tray into a bucket that I empty daily (sitting water can attract unwanted insects). Your environmental conditions will affect how often you need to water your seedlings. Sometimes in the humidity of the summer, I can skip a day of watering because the blocks do not dry out. Once seedlings are established, I do allow them to dry out a little bit in between waterings. This helps prevent algae build up on the blocks. But if you live in an arid climate you may need to water more than once a day. For the most part, I only visit my seeds twice daily. Once early in the morning when they get watered and once in the evening to see how the day has treated them.

Note: Whatever you use for your tray make sure the sides are low enough that you can easily pour the water off the tray without dumping the soil blocks.

Step 3:

Nutrition becomes more important once the seedlings have germinated. The soil medium I use has some nutrients in it but once the seedlings develop their first true set of leaves I begin to feed them with fish emulsion every once or twice a week. I just mix it up according to the instructions on the label and use it in my watering can. If you start to notice discoloring of the leaves (yellowing or purplish appearance) this may be due to a nutritional deficiency.