Vegetable Seed Propagation Strategies

By Louise Placek

Seeds are the way to go if you need large numbers of plants in a relatively short period of time. Many herbs, flowers and vegetables are best started from seed because they sprout and grow quickly for the volume sales of spring and fall. Many perennials also may be grown from seed but generally tend to be slower to germinate and grow out. The biggest advantage of seeds is economy. Compared to the cost of buying plugs, seeds are cheap.


A seeder setup in a plug tray.
A seeder setup in a plug tray. Photo courtesy Made from Scratch.

288 Plug Tray

Unless you are going into the plug growing business or you have ten acres of greenhouses, a simple vacuum seeder is all you need to do enough plugs to keep you in business. There are several companies that make them, but they all operate on the same principle: A small vacuum motor is attached by a flexible hose to a metal box, which has a metal plate on top with small holes. Your seeds will adhere via suction to the metal plate until you turn the vacuum off, after inverting the box over your plug tray.

The plates come in hole patterns that match the plug tray you have decided to use so that when you invert the metal box, (with attached metal plate), over your plug tray, each seed will drop into one cell. They also come in different sized holes to match the seeds you are working with. Most growers use the plug tray with 288 cells, but they range in size from 72 to 512 cells. That is probably clear as mud, but you get the idea.

If you were the real­ly handy type you could make one. But if you aren’t, then the entire setup with several sizes of plates will cost you in the neighborhood of $1,000. That may seem like a lot of money, but I have used the dickens out of mine and it is still rolling along. It has paid for itself many times over considering the cost of purchasing plugs from someone else. You might as well put it in your budget.

There are also trays that have little rows built into them for doing those tiny little seeds the size of dust. I have tried just sprinkling the seeds over the 288-plug tray, which gives you a small bunch of seedlings in each cell, but unless you have a remarkably steady hand you will end up with some cells stuffed with seedlings and some with only a few. I have also tried an open tray, just lightly broadcasting the seeds over the soil surface. Usually this is disastrous because no matter how lightly I think I am broadcasting, I still end up with this mass of seedlings that have to be laboriously teased apart, which is hard on them and on my patience. For really minia­ture seeds, lightly sprinkling in rows will give you something a little easier to work with.

The thing to remember is that some of those tiny seeds turn into rather large plants and so must be transplanted indi­vidually. If you plant something like thyme or Greek oregano in clusters you will have serious crowding in the pot.

The soilless mix I use for my seed trays (and also for some cuttings) is a mixture of 50 percent peat moss, 25 percent medium vermiculite, and 25 percent perlite. I also throw in a little soft rock phosphate and bat guano but that is not abso­lutely necessary. I think it just makes me feel better as I imag­ine I am giving those baby plants a little something to munch on when they put on a show of leaves. The mixture should be slightly moist when you are ready to use it. If it is dry, add water until you get a moist cake consistency.

Fill the plug tray by heaping the soil over the cells and tap­ping the sides to make sure there are no air pockets in the cells. Do not pack it in. You can lightly firm the soil in, but pressing too hard will remove the small air spaces between soil particles which are necessary for good drainage and healthy root devel­opment. Smooth the topsoil off and you are ready to seed your tray. After seeding I use some of the loose plug mixture to lightly cover the seeds that need darkness or soil depth for bet­ter germination. The tiny seeds and the ones that specifically need light for germination I just leave on top of the soil. They will nestle in when you water.

Water your tray immediately with a mister or fogger. Droplets any bigger than this might displace the seeds and/or pack them in too forcefully. Do not ever let your plug trays dry out. They must be watched vigilantly. Misting benches with timers are great if your weather conditions are exactly the same every day. Around here, a very humid, sunny day might follow a humid, cloudy day, which might follow a dry, sunny day. Each of those days will require different water­ing strategies. If you let the plug trays dry out when germina­tion first occurs, you will most likely lose the whole tray. If they dry out severely after the cotyledon stage, the plants that do survive will likely be weak, stunted and generally perform poorly. You might as well start over.

It is a good idea to have a written record of what seeds you sow, when they germinated, and when they were planted. I have developed several different kinds of logs over the years, trying to come up with something that made it so easy that I would have no excuses for not recording my work. The one I am currently using is by far the easiest, but I still procrastinate about logging. The thing is, it is really nice to look back over a season or two to see the patterns of germination. It can be very useful when you are trying to work out your growing plan. It is also an excellent way to track varieties of plants and how they have performed for you.

Source: Made from Scratch