how big should sunflower seedlings be before transplanting outdoors

If you are planting (or have already planted) sunflower seeds, you are probably wondering just how long they take to sprout. You may also be curious about how you can speed up the seed germination process. So, how long do sunflower seeds take to germinate? Sunflower seeds take 4 to 11 days to germinate. Sunflower seeds germinate faster with optimal soil temperature, humidity, air circulation, and planting depth. Of course, you can germinate sunflower seeds indoors and transplant outside later, but it is difficult to do so, and so it is preferable to germinate sunflower seeds directly in the soil outdoors. Let’s take a closer look at some of the factors that affect how long sunflower seeds take to germinate. We’ll also see how we can optimize these factors to encourage faster seed germination. How Long Do Sunflower Seeds Take To Germinate? Sunflower seeds normally take between 4 and 11 days to germinate. This can vary a lot depending on soil temperature and other key germination factors. According to the Iowa State University Extension, sunflower seeds can take as little as 4 days to germinate when planted an inch deep in warm soil. On the other hand, Purdue University suggests that sunflower seeds can take up to 11 days to germinate. Sunflower seeds normally take 4 to 11 days to germinate under good conditions (warm, moist soil). It will all depend on various factors that affect time to seed germination – let’s get into some of those now! What Factors Affect Sunflower Seed Germination? The time a seed takes to germinate depends on several important factors, such as: Soil TemperatureHumidity LevelsAir CirculationPlanting Depth Let’s dive into more detail on these factors, starting with soil temperature. Soil Temperature For Sunflower Seeds According to the North Dakota State University, the minimum temperature for sunflower seed germination is 50 degrees Fahrenheit (10 degrees Celsius). If the soil is any colder than this, you will see low germination rates – that is, if you can get any seeds at all to germinate! This is nature’s way of protecting sunflower seeds from sprouting at a time when they will be unable to survive. (Note: You can find the germination rate on the seed packet itself. For example, if the germination rate is 95%, then you would expect 95 seeds to sprout out of every 100 seeds that you planted.) According to Purdue University, the maximum temperature for sunflower seed germination is 91 degrees Fahrenheit (32.8 degrees Celsius). If the soil is any warmer than this, germination rates will decrease. Combined with high humidity, high temperatures can encourage the growth of mold, which is another threat to your plants. The ideal (optimal) temperature for sunflower seed germination is between 70 degrees Fahrenheit (21.1 degrees Celsius) and 78 degrees Fahrenheit (25.6 degrees Celsius). Keep in mind that these temperatures refer to soil temperature, not air temperature. If you want to find out the soil temperature, use a probe-type thermometer to check. If the thermometer reads a temperature that is too low, then you have some options. One option is to wait until the sun warms up the soil. To speed up this process, clear away any debris, such as leaves or grass clippings, from the soil surface. Also make sure to choose a location for planting that gets plenty of sun, so that it can warm up the soil faster. If you are worried about a short growing season, you can also use a cloche (a plastic or glass cover) to trap some heat and warm up the air and soil near your sunflower seeds. A cloche can be made from a plastic water bottle, and will keep seeds or seedlings warmer than the surrounding air, especially on sunny days. A cloche can be made from a plastic water bottle to trap heat and moisture in a small area to help seeds germinate faster. The table below shows minimum, ideal, and maximum temperatures for sunflower seed germination. SeedTempTemp(degreesF)Temp(degreesC)Min 50 10 Ideal 70 to 78 21 to 26 Max 91 32.8 This table shows minimum, ideal, &maximum temperatures forsunflower seed germination. Humidity For Sunflower Seeds Humidity is another important factor to consider when germinating sunflower seeds. If the air is too dry, then the soil will dry out faster, and the seeds will have trouble germinating – they may even die! If the air is too humid, then the soil will stay too wet, especially if you over water the soil. This can lead to damping off, which occurs when mold or other pathogens affect seeds or seedlings. Damping off is more likely with high humidity levels, in moist soil, and at cooler temperatures. For more information, check out this article on damping off from Wikipedia. If you find that you have trouble keeping the air and soil humid enough, you do have some options. One option is to use a cloche (mentioned earlier). A cloche can be made out of a plastic water bottle to retain heat and moisture for seeds or seedlings. A cloche, if sealed, traps moisture in the air and soil so that seeds have the humid environment they need to germinate properly. A cloche will help your seeds to germinate faster, increase germination rates, and cut down on the time and effort needed to keep soil moist. Air Circulation For Sunflower Seeds Seeds need air, just like seedlings and established plants. If the soil is too wet and there is too little air circulation, it can spell death for your seeds before they even have a chance to sprout. To keep your seeds from suffocating due to lack of air, there are two key things you can do. To get healthy sunflowers, you need to germinate the seeds. One important factor is giving them proper air circulation - do not compact the soil or make it too wet! First, keep the soil moist, but not wet. Do not over water the soil, and consider using a cloche to help you to get the right moisture level. Second, keep the soil loose. Do not compact the soil by pushing down on it either before or after planting your seeds. When there is more space between soil particles, there is more space for air and water, both of which are necessary for seed germination. Planting Depth For Sunflower Seeds Sunflower seeds should be planted 1 to 2 inches deep for ideal germination. If you plant the seeds too deep, they may fail to germinate or reach the soil surface. You can learn more about proper planting depth for seeds in my article here. How Do I Make My Sunflower Seeds Germinate Faster? If you want to make your sunflower seeds germinate faster, there are several important actions you can take. First, protect your seeds from extreme heat and cold. As mentioned earlier, temperature is one of the most important factors that affect seed germination. If it is too cold to plant seeds outside, then start your seeds indoors. This gives you a head start on the growing season, and minimizes the danger of late spring frosts killing your seedlings. This is especially helpful if you live in an area with a short growing season. Second, ensure that the soil is moist (not wet!) and the air is humid. Seeds will not germinate if there is not enough moisture in the soil and air. Consider a cloche for this purpose. Third, make sure that the soil has enough air circulation. This means that you should avoid compacted soil both before and after planting. It also means that you should avoid over watering your soil. Fourth, remember that sunflower seeds do not need light to germinate. If you start sunflower seeds indoors, give the seedlings bright overhead lights after germination. Sunflower seeds do not need light to germinate, but you should provide overhead lights for seedlings after they emerge when growing indoors. Fifth, make sure to plant your sunflower seeds according to the proper depth and spacing. Sunflower seeds should be planted at a depth of 1 to 2 inches (2.5 to 5.1 centimeters). If planting in rows, space plants 6 inches apart (2 per foot). When the first true leaves appear, thin the plants to 1 per 2 feet to prevent competition between plants. For more information, check out this article on sunflowers from the Burpee website. Finally, you can scarify (scratch the surface) of your seeds in order to encourage germination. This can speed up germination and also increase germination rate (the percentage of seeds that sprout). For more information, check out this article on seeds and seedlings from the Penn State University Extension. Should Sunflower Seeds Be Soaked Before Planting? You can soak your sunflower seeds before planting to encourage faster germination. Put them in clean water and let them sit for up to 24 hours before planting. However, this is not required – as long as the growing medium is moist and warm, the sunflower seeds should germinate well. Can You Germinate Sunflower Seeds In A Paper Towel? Yes, you can germinate sunflower seeds in a paper towel. The paper towel holds moisture and allows the seeds to breathe, serving as an alternative growing medium. You can germinate sunflower seeds in a damp paper towel, but you will soon need to transplant them into soil so that they can continue growing. To germinate sunflower seeds on a paper towel, wet the paper towel until it is damp (not soaking wet). Then, lay out the sunflower seeds so that they are separated (not touching). Be sure to keep the paper towel and seeds in a warm place, to encourage faster germination and higher germination rates. The only drawback of this method is that you will need to transplant the sprouted seeds into soil by hand, since they will soon need nutrients from the soil to grow and establish stronger roots. Be gentle when handling the tiny sprouted seedlings! Germinating sunflower seeds in a paper towel may be helpful if you live in an area with a short growing season. Why Are My Sunflower Seeds Not Sprouting? There are a couple of possible reasons that your sunflower seeds are not germinating. Your Sunflower Seeds Are Too Old One common reason for a lack of germination is that the seeds you are using are too old. In that case, the germination rate may be low, or even zero. Sunflower seeds tend to last 2 to 3 years. Beyond that, you will see lower germination rates from planted seeds. Sunflower (helianthus) seeds tend to last about 2 to 3 years, and germination rates will naturally decrease with each passing year. For more information, check out this article from Clear Creek Seeds. Your Soil Is Too Cold Or Dry Another reason your sunflower seeds are not germinating has to do with soil conditions. If the soil is too cold, then your sunflower seeds might not sprout right away (whether you are growing indoors or outdoors). They may sprout when conditions improve and the soil warms up. The Old Farmer’s Almanac suggests planting sunflower seeds after the last danger of frost has passed (mid-April to late-May in northern regions. Wait until after the last frost to plant sunflower seeds outside. Don’t wait too long to plant, because if soil temperatures get warmer than 78 degrees Fahrenheit (25.6 degrees Celsius), then your sunflower seeds will germinate more slowly, and at lower rates. You can find information on frost dates on the Old Farmer’s Almanac website. Finally, remember that if the soil is too dry, then seeds will not germinate, and they may even die before you have a chance to correct the problem. Keep the soil moist, and consider using a humidity dome to help maintain the proper moisture levels in the soil and air. How Big Should Sunflower Seedlings Be Before Transplanting Outdoors? Generally, sunflower seeds should be planted directly in the soil outdoors. If this is not possible, then transplant them outdoors within 3 weeks of planting seeds. For more information, check out this article on sunflowers from the Cornell University Extension. Conclusion By now, you have a good idea of how long it takes sunflower seeds to germinate. You also know about the factors that affect time to germination, how to optimize for faster germination, and how to troubleshoot a lack of germination. I hope you found this article helpful – if so, please share it with someone who can use the information. If you have any questions about sunflower seed germination, please leave a comment below.