Starting Seeds Indoors

Starting Seeds Indoor Photo by John Cappadonna

By John Cappadonna – Master Gardener

It is time to start seeds indoors for spring planting. When you get seeds from a supplier, they are dry and dormant. Typically, moisture and temperature are the factors that break that dormancy, but sometimes light or darkness play a role.

Until the seedling forms true leaves, the endosperm portion of the seed, along with oxygen in the soil, furnishes the nutrients for the seedling to grow. This is why it is essential to use a light-textured seed-starting mixture that drains well when starting your seeds. Be careful not to overwater. Too much water displaces oxygen and promotes the growth of pathogens that can cause damping-off disease.

A study from North Carolina State found that covering seeds with fine vermiculite rather than the planting medium yielded the best results. Regardless of the seed-starting mixture, covering with vermiculite worked better than any of the mixtures alone. Perhaps it is the ability to hold moisture while maintaining the tiny spaces that contain oxygen that is the reason. I do know it works, and I make sure to have it on hand when seed starting time comes around. I think another reason it works well is that vermiculite does not form a crust, and emerging seedlings push through easily while the root grows down into the planting medium.

Some plants, like tomatoes, have seeds with well-developed embryos that germinate very quickly. Often, tomatoes under optimum conditions will germinate in just two days. Not all seeds germinate quickly. Parsley, for example, has seeds with embryos that require some time to develop more before sprouting, so it takes longer for the seedlings to emerge. Some seeds, like spinach, contain natural chemical compounds that inhibit germination, and these compounds must break down in the soil before germination occurs. Some seeds require light to germinate. A couple that come to mind are thyme and oregano. Both their seeds are very small and germinate best when sprinkled on the soil surface. On the other side of the coin, some seeds need darkness to germinate best. Peas are an example of this.

In addition to water and light, temperature is very critical for optimum germination. Optimum means conditions most conducive to a favorable outcome. So, the optimum temperature is the one at which the seeds germinate best. Most seeds have a range of temperatures at which they will germinate, but the farther the temperature is from the optimum, the lower the germination rate will be. I like to buy seed from companies that publish this information. Seed companies test lots of seeds, and some publish the germination rate and the optimal germination temperature.

Using a heat mat with a thermostatic control will enable you to control bottom heat in the soil precisely and, consequently, the seed. I use 50-cell plug trays and shallow humidity domes to start my seeds, but as soon as germination begins, the domes need to come off.

Good LED grow lights are a must. Once the seedlings develop true leaves, they begin to manufacture their own food, but they need adequate light to do it.

Once you learn the requirements of each seed, starting and growing your own seedlings becomes easier, and it is a fascinating facet of gardening that I enjoy.

If you have questions, call the AgriLife office in Odessa at 498-4071 or in Midland at 686-4700.   Additional information and access to past articles are available at westtexasgardening.org.  Click on “Resources.”