Late winter and early spring are ideal months to start your spring and summer vegetable plants indoors, giving them a jump start, so they are ready to be moved outdoors once the chance of frost has passed. This article contains tips for successful seed starting and saving money while doing so.
Seed starting can be expensive. After buying seeds, starter trays or flats, plugs, pots, and packaged seed-starting mixes, the costs add up. There are several solutions to minimize costs. You can make seed starting mix and use everyday household items to plant your seeds.
Not all plants need to be started indoors or in a greenhouse. However, peppers are tomatoes are best started from seed indoors and transplanted outside after the last chance of frost and once the soil is warmer. Especially in the case of tomatoes, getting a jump start on the growing season ensures a good harvest 1) before it gets too hot for fruit to set and for the plants to survive the summer (if your garden is located in a hot climate) or 2) to ensure a good crop before fall frost, in areas with shorter summers.
Lettuces, artichokes, asparagus, broccoli, cabbage, and cauliflower are also often planted outdoors as transplants. Check the publication AZ1005-2018, Vegetable Planting Calendar for Maricopa County, for details on vegetables to be started from transplants.
Reduce Expenses: Mix Your Planting Media & Use Recycled Containers
One method of keeping costs down is to make your media mix. The mix can be soilless or contain soil and compost. If you use soil or compost, it should be heat pasteurized (heat sterilized) to prevent damping off and other seedling diseases caused by viruses, bacteria, and fungi. More on that later.
Soil-based media mixes
Research has shown that organic materials that have been adequately composted can be used in potting mixes. (1)
While it is possible to use 100% compost for container-grown seeds, there are drawbacks to this method. A commonly accepted recommendation is to use compost at about 30-40% by volume. Compost and supplies nutrients and other compounds that promote plant growth and health. However, most composts are too heavy, hold too much water or drain too much (inconsistency), or have too high a starting Electrical Conductivity (EC) to be used 100% in a seed-starting mix. (2) EC is the most common measure of soil salinity.
Simple 1:1:1 Soil mix recipe
1 part finely screened compost
1 part field or garden soil
1 part sharp sand* or perlite
Limestone (if needed to increase pH)**
*Sharp sand is also known as river sand or builder’s sand. It is different than playground-type smoothed-grain sand.
**For optimum seed germination, most crops prefer a growing media with a pH of 5.7 to 6.2.
A soilless mix typically contains peat or coconut coir, perlite, vermiculite, and sand. Soilless blends help prevent disease and fungus gnats. Peat is one of the most useful of substrates because its fibrous structure helps it retain water and air. However, there is concern over the ecological effects of excavating peat moss. It can take 25 years for an inch of peat to form in a bog, so peat is not easily “renewable.” Ground-up coconut husk fibers (coir) is a popular alternative, though the sustainability of harvesting and shipping this material from the tropics is also debated. (3)
What’s the difference between perlite and vermiculite?
Perlite and vermiculite have similarities. Both are processed volcanic rock. Heat or steam is used to expand the minerals which drastically reduces weight and creates pores in the pieces. Both products are inert and sterile.
Vermiculite is usually a shade of brown. It helps Improves soil structure through soil aeration, holds water well, holds nutrients in the mix, and contains some calcium and magnesium. Vermiculite helps regulate the amount of water available to seeds to prevent the saturating, drying out, saturating process that can occur with compost and soil. It has a near-neutral pH. Vermiculite comes in different grades; medium or fine grade is usually used for starting seeds. (4)
Perlite looks like tiny white balls of Styrofoam. It improves aeration and drainage by preventing the caking or compaction of other materials. Perlite provides space for roots and shoots to move through the soil. It is lightweight, sterile, and has a neutral pH. (4)
Perlite and vermiculite are both dusty; avoid breathing the dust by dampening the mix before using it.
Vermiculite (left) and Perlite
Another method of saving money is to skip buying plugs, flats, and pots, and use your own recycled or common household materials. Almost any clean container may be used for seed starting provided it allows for good drainage and is at least 2" deep. Save money by re-using cottage cheese and yogurt containers, foam and plastic drink cups, paper towel and toilet paper rolls, milk and water jugs, cartons, aluminum pans, and clear clamshells from grocery stores. I often re-use plastic or foam cups, poke a few holes in the bottom, and use a cat food can underneath to catch water runoff.
Preventing Seedling Disease: Dampening Off
“Dampening off” is a collective term for diseases that beset seedlings. Dampening occurs when young seeding sprout but then die rather suddenly. Viruses, bacteria, and fungi that are present in the soil infect the young plants and cause damage or death. The moisture and heat in the substrate – which we apply for the benefit of the seeds – helps pathogens multiply as well. Harmful nematodes may also be present in the soil.
Diseases are more likely to be present when garden soil or compost is used in the seed media, but they can also be spread by infected tools, pots, containers, hands, anything that contacts the substrate.
If you are using soil or compost in your media mix, pasteurization is a method of killing most pathogens and nematodes. In their book Cutting Propagation: A Guide to Propagating and Producing Floriculture Crops, John Dole and James Gibson describe an effective method of pasteurization for substrates. Heat the media to 140-150° Fahrenheit for 30 minutes. (5) This process can be completed in your oven using an old baking pan, or outdoors on a sunny day using a plastic bag. If heating with the sun, insert a thermometer to ensure the 140-degree minimum is obtained.
Ideal conditions for seed starting (heat, light, air & water)
Seeds remain dormant or inactive until conditions are right for germination. All seeds need water, oxygen, and proper temperature to germinate. The reason for adequate attention to the planting media is to create the ideal conditions for water and oxygen. As for heat, if you start seeds indoors, most plants will have enough warmth to germinate. Peppers, for example, need a minimum of 60°F soil temperature with an optimal 65-75°F. Tomatoes need a minimum of 50 degrees, with an optimal of 65-85°F. For other vegetables, refer to this chart, based on publication GN 154 from the California Cooperative Extension - Sacramento County.
If you are starting seeds in an outdoor greenhouse, monitor day and nighttime temperatures inside the structure. Supplemental heat may be necessary and can be provided by a heat lamp or heating mat.
When to Fertilize Seedlings
Seedlings draw energy for germination from nutrients stored in the seed and do not need fertilizer until they have several sets of true leaves. At that point, seedlings will benefit from a weak general-purpose water-soluble fertilizer mixed 1/4 strength. Fertilize only once a week. (1)
Plants started indoors will not have been exposed to full sun, wind, or fluctuating temperatures. If seedlings are not gradually accustomed to the outdoor environment, a process called "hardening off," their leaves may be scorched by sun or wind. They may wilt and die.
Two weeks before planting outdoors, it is time to start hardening off your plants. Start by putting them outside a few hours day, in the shade, during the warmth of the afternoon, protected from the wind.
Bring the seedlings inside before temperatures start to drop in the evening. Each day leave the plants out longer and expose them to more direct sunshine. By the end of two weeks, unless freezing temperatures are forecast, the seedlings can stay outside in a sunny area until you are ready to transplant them into the garden. (1)
Another option is to plant the seedlings outdoors earlier (or set their containers out earlier) and use a temporary cloche or cover to prevent damage from wind, heavy rains, and cold or frost while the plants are adjusting.
Finally, Don’t Forget to Check your Seed Packets
Many of us gardeners have an extensive collection of seeds and have difficulty resisting buying or collecting more. However, the viability of seed deteriorates over time, so if some of your seeds are older than a year or two, you can do a germination test before planting a large group.
Seed germination test:
Spread a paper towel on a waterproof surface.
Wet the paper with water and allow excess water to drip for about a minute.
Count a set amount of seeds (20, 50, etc.) and place them on one half of the wet paper towel. (Mix the seed well to ensure the sample is representative of the whole seed lot.)
Fold the sheet over so that the half without the seeds is on top of the seeds.
Roll the towel into a moderate tight tube.
Put the tube into a zip lock bag and place the bag in a warm spot (70 to 85°F).
Make a count of germinated seed every two to three days and remove seeds with a visible radicle.
Most vegetable seeds will germinate within one to three weeks depending on the species.
At the end of the germination test, the number of seeds that germinated divided by the total tested results in a percent germination rate. (6)
Finally, check the “date to maturity” on your varieties. Shorter time frames are beneficial in our area, because we have four distinct growing seasons, unlike more northern parts of the country. For example, we want to get the tomato harvest maximized before the heat gets too high for the plants to set fruit. Although with care and lots of shade you may be able to baby some tomatoes through summer, they won’t produce much, if any, fruit after the heat is consistently over 90°F day and 75°F at night.
University of Minnesota Extension. (“Reviewed 2018”). Starting Seeds Indoors. Retrieved 1/13/2020 from https://extension.umn.edu/planting-and-growing-guides/starting-seeds-indoors.
University of Massachusetts - Amherst, Center for Agriculture, Food and the Environment. (n.d.). Retrieved from https://ag.umass.edu/greenhouse-floriculture/greenhouse-best-management-practices-bmp-manual/effects-of-growing-media-on
University of Maryland Extension, Home and Garden Information Center. (n.d.) Containers and Growing Medium for Seed Starting. Retrieved 1/10/2020 from https://extension.umd.edu/hgic/topics/containers-and-growing-medium-seed-starting
Marion, L. [MIGardener]. (2019, Apr 11) Perlite vs. Vermiculite Uses, Differences, and Misconceptions [Video file]. Retrieved from https://youtu.be/E4J2L0Hi_fk
Dole, J.M. and Gibson, J.L. (2006). Cutting Propagation: A Guide to Propagating and Producing Floriculture Crops. West Chicago, IL: Ball Publishing.
Ngouajio, M. (2009, May 13). A simple seed germination test may be a deal breaker. Michigan State University, MSU Extension. Retrieved Jan 13, 2020 from https://www.canr.msu.edu/news/a_simple_seed_germination_test_may_be_a_deal_breaker