INDOOR SEED STARTING WITH SOIL BLOCKS
Starting seedlings indoors is my go-to process for almost everything that I grow in the garden and greenhouse. For the short season here in our high altitude location, this is especially important. It allows a head start on plants that need time to grow, and starting seeds in the warm, protected conditions indoors makes for healthier plants. There are many ways to do this, using greenhouses, grow lights, grow mats, seedling trays, plugs, peat pots, etc. Everyone has their favorite method, as do I.
I use “SOIL BLOCKS” to start all my seedlings indoors under grow lights. The only seeds I will direct-seed outdoors are peas & carrots. Although it is usually recommended to start beans, beets & corn outside (it is said that they don’t transplant well), I’ve had great success by starting all of these indoors. Although the greenhouse is quite conducive to starting things directly in the beds, I normally begin my greenhouse vegetables in the soil blocks also, which allows me to get new plants started while other plants are still filling the beds. After plants are harvested, I’m ready to re-plant the spot with something that’s already gotten a good start.
The soil blocks are made with block makers made by Ladbrooke Soil Blockers. They can be found at several garden supply websites such as GrowOrganic.com or JohnnySeeds.com, along with information about using them. It’s a bit of an investment, but these blockers make great plant starts with a high success rate and the block makers last a long time. I’ve been using mine now for 9 years. If you don’t want to spend the money, there are instructions for making your own DIY block makers found on several sites on the internet. Making the blocks takes a little practice and some trial and error, but after a little practice, it’s “as easy as pie” — mud pie, that is. The blocks are easy to transplant—no trying to remove them from small pots or carefully separate them out of seeding trays. My experience with peat pots or newspaper pots are that they work ok, but it still takes time for them to break down for roots to get through. The soil blocks make transplanting easy both for you and for the plants.
It’s helpful to read the booklet, “Transplants in Soil Blocks” by David Tresemer. He did a lot of research using this method, and explains which seeds can be started in soil blocks, as well as how many seeds can be planted in each block (for multiplanting), etc. To make the blocks, I use a recipe which uses peat or coco, perlite, compost, and some various minerals and nutrients. The soil block mix recipes I use can be found here.
Update: I used to start many seedlings in the “micro” blocks shown here, but over time I’ve abandoned this method mostly because I am growing fewer things at a time and find it just as easy to start directly in the “mini” blocks. I’m leaving my thoughts about the micro blocks here fyi.
Germination can start for many of the smaller size seeds (flowers, herbs, etc.) in the 3/4″ MICRO blocks shown here. This gives them a chance to start in a cozy, warm, small space, with very little soil. The Ladbrooke blocker to make these makes 20 small blocks at a time. I put them in these inexpensive cake pans, or other plastic containers saved from frozen meals. The seeds start more quickly in these small blocks and nutrient-rich soil than they would outside. One benefit of starting seeds this way is that when seeds don’t sprout, you haven’t wasted much space or material. It’s important to keep these small seeds & seedlings moist, but not too wet while in these blocks. I usually keep a sprayer handy and spray them a couple of times a day, with some extra water in the tray for bottom watering. Until the seedlings emerge, I keep a lid on loosely, and keep the trays on TOP of my grow lights, to allow for bottom warmth. Once they emerge, they go under the lights, which are kept about 2” above the seedlings. If they do get too dry, not to worry, they’ll usually perk up just fine after some water is applied.
Update: These 2″ blocks, the “mini” blocks, are now what I use exclusively rather than starting with the micro blocks. I simply start the seeds directly in these to transplant later either directly to the garden or to the “maxi” blocks shown below. To start directly in the mini blocks, there are interchangeable plugs for these block makers to make different size indentations to place the seeds. I use a smaller one than the cube-size shown here to start seeds directly in the mini blocks. The micro-to-mini block instructions are here fyi.
After the seeds sprout in the micro blocks and appear to be established, they can easily be transferred to blocks slightly larger, where the roots will have more room to grow. This shows the micro blocks placed into the mini blocks. After seeds have begun to grow, they are transplanted into 2″ MINI blocks, The 2″ mini blocks can be made with a cube-shaped hole in the middle just the right size to fit the ¾” micros. The photo here shows how nicely they fit. This gives the seedlings a chance to grow more before being transplanted either outdoors or into MAXI blocks for further growth indoors.
Larger seeds, or seeds that grow very quickly, such as tomatoes, peppers, beets, squash, and even corn & beans can be started directly in the 2″ mini block, which can be made with a ½” or 1″ dimple in which to place the seeds. With this method I even start my corn and beans in blocks, although most garden resources indicate they should not be started indoors and that they don’t transplant well. In our short growing season it gives them a nice head start, and when transplanted outside I have nice, even rows of things that have all germinated–no empty spaces from sprouting failures. I also use aluminum cake pans for these, with 20 blocks per tray, loosely covered with the plastic lids that come with the trays, until seedlings are too large for the lid. Many seedlings can stay in this size block until being planted in the garden, others may need to be transplanted again, into larger blocks.
After plants begin to outgrow the 2” mini blocks but need to remain indoors for more growth, they can be transplanted into the 4″ maxi block until they are ready to be transplanted outside. These blocks are made with a 2″ cube indentation, just about the right size to fit the 2″ blocks.
I feel that the cube indentation is a bit short for many of the seedlings, such as tomatoes, which can be buried more deeply up the stem. To make more space I will dig about 1/4-1/2″ of the soil out with a kitchen fork from the bottom of each block’s indentation. After putting the smaller block into the larger, I add some soil at the top and bury the stem just a little more.
The seedlings grow fast under lights. See how healthy they are after being started and transplanted to the maxi blocks under lights! These tomatoes (2013) were started at 8 weeks before the last frost, and were ready to go outside, but the outside wasn’t quite ready for them. They got a bit taller than I’d like prior to planting out. They don’t really gain much by being started too soon before going outside. I believe 6-7 weeks is plenty of time for tomatoes to get a good start, and if the weather should be too nasty for them to be planted out, another week inside won’t cause any harm. See how nice and leafy these plants are?
Many plants started indoors or in greenhouses in small pots get too tall and leggy. At the right is a photo of my first year’s tomato plants, before I began to use the soil blocks. A good way to keep them from getting too tall indoors is to keep the lights just a couple of inches above the top of the plants. It’s also helpful to put a fan on them a portion of each day, or to wiggle them with your hands a bit, to strengthen the stems. This is particularly helpful if your location is windy—they need to get ready to withstand that wind outside!
Below is a photo of one of my tomatoes in 2017, just prior to planting. It is not too tall, dark green, and it should grow well after being planted outside.
After getting a good start indoors, planting out is a cinch, and there is a better chance of a good harvest in our high altitude short season.
KEEPING TRACK OF SEEDLINGS
When using these micro and mini blocks it can be difficult to know which blocks are which seeds! There is no container to mark on the side, and no room for a name-stake. The aluminum cake pans I use will hold 20 mini-blocks, or 120 micro-blocks. I have made up sheets I can use to pencil in the seeds I have planted. They will look something like this. Each sheet shows 3 trays of seeds. I mark the side of each tray with the date and tray # so I know which side is up. They look something like this.
Now that I have the greenhouse going year-round, I’ve found that it is quite a project to see that it is put to its full use. I want to be ready to replant each area as they become ready for new plants. I make a guess as to how long each plant will remain in place until harvested and removed, and use my grow lights to start seedlings that will be ready to put in place of those plants.
The greenhouse and its soil are warm enough to start seeds directly in the beds, and in some cases, after plants are harvested, I do that. But the grow lights are a handy way to keep the greenhouse full!