Early to mid-March is the best time to plant early season cold-tolerant plants like broccoli, cabbage, and head lettuce, and long-season heat-loving plants like peppers, okra, and eggplant. If you mainly just start tomatoes at home, you can wait until early April.
In general, you should start seeds indoors 6 to 8 weeks before the average last frost date in your area. For example, our average last frost date here in growing zone 4b (Minneapolis, MN) is May 15th.
Fall Planting Results in Earlier Blooms
Like fall-seeded lawns, fall-planted wildflower seed has a chance to "settle" into your site during the winter, and is ready to burst into growth in early spring. This is why fall-planted wildflower seed is up and in bloom about two weeks earlier than spring-planted seed.
The closer the temperature is to optimum, the quicker germination will occur. Most seeds germinate when the soil temperature is between 68° and 86°F. Once germination occurs, the optimum growing temperature for the seedling is about 10°F cooler than the optimum germination temperature.
When should you start seeds indoors? Start seeds six to eight weeks before the last frost in your area. 2 Most plants are ready to go outside four to six weeks after you start the seeds.
Most seeds will not germinate without sunlight and will perform best with 12 to 16 hours each day. Indoors, place seed containers in a sunny, south-facing window and give the container a quarter turn each day to prevent the seedlings from overreaching toward the light and developing weak, elongated stems.
All seeds need water, oxygen, and proper temperature in order to germinate. Some seeds require proper light also.
Temperature influences the moisture content, hormone function, and enzyme activity that occurs during seed germination. Warm temperatures accelerate the chemical reactions in seeds and accelerate cell formation for development.
Soaking your seeds in hot water held to a specific temperature will also break down the seed coating. But this one is a double-edged sword. Soaking seeds in hot water will help speed up germination but can come at the cost of lower germination rates.
Fall is the best time. The autumn season comes with a mix of warm soil and cool air, perfect for planting grass seed and allowing time for new grass roots to develop before winter sets in. It is also a good time to fertilize to build stronger, deeper roots for winter, resulting in a thicker, greener lawn next spring.
By midsummer you should be knee-deep in tomatoes, beans, zucchini, and peppers, so it can be hard to remind yourself to shop for seeds for your next season of vegetable gardening. However, July and August are the best time to get a start on fall and winter food gardening.
Most of the seeds germinate best in dark environments. The presence of light tends to inhibit their growth. The light decomposes carbonic acid gas and expels oxygen which leads the seed to harden. These gases are key factors that promote germination.
Until seeds have sprouted, keep the seed bed moist, never allowing it to dry out. Water with a fine-spray hose nozzle or watering can which will provide a fine misty spray and not wash away the soil. Water often enough (usually about once a day) so that the soil surface never dries out, but remains constantly moist.
Some are quick to germinate, taking 1-2 weeks at most, such as chillies, beans, sunflowers and pumpkins. Some seeds take more like 2-4 weeks, such as mango and parsley. Others, depending on how warm/cold it is, take closer to 2 months, for example avocado.
Not all seeds have the same light requirements. Most seeds germinate best under dark conditions and might even be inhibited by light (e.g., Phacelia and Allium spp.). However, some species (e.g., Begonia, Primula, Coleus) need light to germinate (Miles and Brown 2007).
Paper towels, filter paper or even newspaper provides an excellent medium for germinating seeds. They are pathogen-free and make it easy to control the moisture content for proper germination. This method also takes the guesswork out of knowing if your seeds have germinated since you can easily observe them.
Some seeds take a long time to germinate, and seed soaking can help to speed up the process. By soaking seeds in lukewarm water for 8-12 hours (some can go up to 24 hours, but never more than that), you help the seed to break dormancy and germinate faster.
Germination depends on several environmental factors, e.g., water, oxygen, temperature, and often light and nitrate as well. Of these, water is the most essential factor.
Any soil can be warmed up by covering it over with black plastic, row covers or garden fleece. This technique is particularly useful for heavy or clay soils that retain a lot of moisture. Black plastic works best because dark colours absorb more sunlight, creating warmer conditions beneath.
One of the most popular ways to germinate seeds is the paper towel method.
Some seeds like Allium 'Purple Sensation' and Eryngium giganteum need a long period of cold-moist stratification with alternating temperatures. These are the most difficult seeds to germinate.
Soaking can accelerate germination and increase the proportion of seeds that successfully germinate. Seeds have evolved a protective coating around the embryo so the embryo can survive being dispersed by some means. The coating protects the seeds until they find themselves in a suitable place to grow into a new plant.
As a general rule of thumb, your seeds will sprout even if you don't soak your seeds before planting, but with soaking, the germination time decreases, and the germination rate increases. Seeds that have a continual flow of moisture to uptake have much higher chances of success.