Starter's Guide to Sowing Seeds

A Starter's Guide to Sowing Seeds

Germination goes better when the soil is more than backyard dirt

Soil pH is just one of several factors that can determine whether a seed developers into a thriving plant or fails to grow at all. We explain here how the savvy gardener can give seeds a helpful head start in life:

When should I start seed?

Most seed packages come with full instructions on when to start the seed. As a rule or thumb, most annual vegetable and flower seed should be started about six to eight weeks before the average last frost date in your area.

What is the best soil medium?

Always use a germination mixture that has been specially formulated to spur growth. Homemade soil mixtures are easy to make and they are cheaper than buying premade ones, especially if you start large quantities of seed.

One of the best recipes is Cornell Peat-Lite, developed by horticulturists and agronomists at Cornell University. Its ingredients include: 1 bushel of shredded sphagnum peat meat; 1 bushel of horticultural vermiculite (no. 4-fine); 4 level table-spoonfuls of ammonium nitrate (a nitrogen source); 2 level tablespoonfuls of powdered superphosphate (20 percent); and 10 level tablespoonfuls of finely ground dolomitic limestone.

Never use soil from the yard or garden as your germination medium unless it is sterilized and combined with materials such as vermiculite, perlite, and horticultural sand. The mixture should be light and almost fluffy even after it is watered.

To sterilize a seed medium in an oven or microwave, you can use a medium-sized potato as your sterility gauge. Place the soil medium in the oven at the same depth as you would need to fill a seed flat. When the potato is cooked enough to be eaten, the soil should be clean enough for your seeds. Photo by Elena.

What is the right temperature for planting?

Most seedlings do best with “warm feet and cool heads.” Make sure soil temperatures are at least 70 to 80F. Air temperature can be about 10 degrees cooler at night. Heat cables or heat mats are placed under germination containers to ensure soil temperatures that are evenly warm throughout. They are inexpensive and can be found in many garden-supply catalogs and most garden centers.

How much watering is necessary?

Water immediately after sowing seeds. Use a spitzer bottle to evenly moisten the surface. The most common mistake is applying too much or too little water. Just keep seeds and seedling evenly moist and never allow seeds to dry out, even temporarily.

How much lignt do seeds need?

Some seeds need light to germinate, some need darkness, Once germinated, however, all seeds need bright light to develop. Light can come from a sunny window – south is best – or fluorescent lighting. Most seedlings need at least 12 to 16 hours of light each day.

To sterilize a seed medium in an oven or microwave, you can use a medium-sized potato as your sterility gauge. Place the soil medium in the oven at the same depth as you would need to fill a seed flat. When the potato is cooked enough to be eaten, the soil should be clean enough for your seeds.

If you are using fluorescent light, seedlings need about 15 to 20 watts per square foor of growing area. A double row of fluorescent tubes is enough for flats that are up to 16 inches wide. Place the light tube about 4 inches above the plants. Don't forget to raise the light tubes as the plants grow.

When should seedlings be thinned out or transplanted?

After the seedlings have germinated and developed at least two leaves, thin them out with scissors at soil level so remaining seedlings are an inch apart. If seedlings aren't thinned out, they will get crowded and become thin, weak, and disease-prone. Transplant seedlings to wider and deeper containers after they have developed at least two to four leaves. Transplanting allows seedlings to develop a stronger root system before being planted outdoors.

What kind of soil do seedlings need when they are moved outside?

Good growing soils are fertile, well drained, and well aerated. When you pick up a handful of earth, it should have a crumbly texture and be filled with worms and other enriching organisms. To prepare outside plots for planting, add at least 3 to 4 inches of organic matter to your garden beds every spring or fall. Work in the organic matter to a depth of at least 12 inches. If you are working with soil that has a lot of heavy clay or sand, add more organic matter and work it in several inches deeper, both in the spring and in the fall. If your soil is poorly drained, you may need to add sand or even put in drainage pipes.

What is the importance of soil pH?

A soil's pH number indicates its level of acidity (sourness) and alkalinity (sweetness). The pH scale ranges from 1 to 14 with 7 being neutral. Numbers below 7 indicate more acidic levels and numbers over 7 indicate alkaline conditions. Most garden plants, flowers, and vegetables prefer a slightly acidic soil pH of 6.2 to 6.8 – about the same acidity as pure water. The pH scale is logarithmic, which means that a soil pH of 5 is 10 times more acidic than a pH of 4.

How do I know what my soil pH is?

As a general rule, if you live in an area with little rainfall and high temperatures, like New Mexico or Arizona, you probably have alkaline soils. If you live in a region with a lot of rain and a temperate climate, as in the northeastern states, the soil is probably acidic. To get an exact soil pH reading, you will need to get your soil tested. Most county extension agencies will do such an analysis free of charge if you bring a sample to them. They are listed in the blue government services pages of the telephone book. Extension agencies can also analyze your soil's nutrient levels and let you know if you need to add any nutrients.

How reliable are pH home test kits?

Although they are not as accurate as soil-testing labs, home test kits will give you a fairly general pH measurement. You can buy such do-it-yourself soil testing kits from garden catalogs or from a well-stocked gardening center. Just be sure to follow all directions carefully to get the best results.

What should I do if the pH level is off?

Soil pH can be lowered – that is, made more acidic – by adding a combination of ground sulfur, aluminum sulfate, iron sulfate, and garden gypsum. In addition, pine needles, pine bark, and peat moss will slowly bring about slight drops in pH levels naturally. To raise pH, you can add agricultural or dolomitic limestone to your soil.