Sunflowers are an iconic plant with the ability to add a pop of color to any garden or area. Gardeners love them because they’re fairly straightforward to grow with little maintenance needed, they look great, and they attract bees and birds.
If you’re thinking of growing your own sunflowers at home, it’s important to understand the basics of sunflower watering from seed to maturity in order to produce the healthiest, most vivid blooms.
How Much Water Do Sunflowers Need?
On page 17 of this pdf about sunflower production there is Table 7 that lists the amount of water a sunflower plant should get based on the week of growth the plant is in and the average air temperature.
The numbers in the graph are based on air temperatures between 70-79 degrees. If during weeks 6-9 air temperatures were between 80-89 degrees it would call for 1.75 inches of water per week and if temperatures were above 90 degrees, 2.1 inches of water per week.
So, if there’s hot weather you probably should water more. Mulching on top of soil can mitigate this by keeping soil cool and helping it to retain moisture.
The amount of water a sunflower needs varies depending on multiple factors. The life cycle stage that the plant is in as well as the temperature and how much rain has fallen all play a key role in determining how much water your sunflowers will need.
In this pdf on sunflower care you can see that the critical stage for watering is from day 45-85 after sprouting. This is the time when the flower head starts to develop to when it is in full bloom.
This is similar to most garden plants in that the most need for water and nutrition is during the flowering and producing fruit phase, or seeds in the sunflowers case.
The numbers above include rainfall. To get an idea of how much rain is expected we use wunderground.com. To know the actual rainfall amount you can use a container around the house or a wide mouthed rain gauge.
The Department of Agronomy at the University of Missouri recommends keeping the soil very moist while a sunflower is germinating. Moisture is critical for a seed germination as it activates catalysts within the seed, mixes with starches or proteins within the seed to from a soluble that will feed the small plant embryo, and softens the shell of the seed making it easier for the seedling to sprout.
How Often To Water Sunflowers
With their tall stems and large blooms, one might think that sunflowers need near-constant attention and watering. Luckily however, this is not the case. Sunflowers are actually quite drought resistant due to their long, branching roots.
This means that they can continue accessing water even when it is deep down in the soil, making them less high-maintenance than your typical garden plant.
When you first plant your sunflowers, water the soil lightly and regularly to retain near-constant moisture until the seeds germinate.
You should water sunflower plants 1-3x a week depending on air temperatures, rainfall, and the stage of growth the plants are in. To know if you need to water or not feel the soil about 3″ down. If it is mostly moist let it be and if it is mostly dry, water.
Feel the soil between your fingers to get an idea of the consistency when it is mostly dry and wet. Monitor your sunflowers for signs of drought or overwatering and adjust the frequency of irrigation as needed.
How Deep Do Sunflower Roots Grow?
Sunflowers need to put down long, branching roots in order to support their tall height and access as much water and nutrients from the soil as possible.
A sunflower will grow one long, primary taproot which extends deep down into the soil, while having many smaller, secondary roots branching off of it.
The sunflower tap root has been known to reach up to 15 feet down into the soil but will regularly be between 30-50″ down! (The US Sunflower Industry, Page 2)
Of course, if you are growing sunflowers in a home garden or container, this imposes space restrictions on the plant. Your sunflower’s roots might not grow as deep as they would if they had unlimited soil depth to access.
Also different cultivars or types of sunflowers tend to have different average root depths; for example, a dwarf cultivar’s roots will never grow as deep as those of a giant cultivar.
If you’re deciding on a sunflower to plant at home, research the particular cultivar you want to grow to determine what root depth you can expect. Then, make a decision based on how much space you have allotted for your sunflowers.
Can You Overwater Sunflowers?
Like any other plant, sunflowers need water to grow and thrive. However, sometimes too much of a good thing is a bad thing.
When the soil is oversaturated with moisture and not draining your sunflower’s roots will constantly be water-logged. Soggy roots lead to problems like root rot, mildew, and diseases that can lead to the death of the plants.
Always keep an eye out for standing water around the base of the plants. If there is standing water 24 hours after the last rainfall or watering something is wrong and you’ll likely need to move the plants to a different area with better draining soil.
Feel the soil around the base of your sunflower before watering; if the soil is still dark and moist, skip that watering and re-check the soil moisture the next day.
Watering Sunflowers in Pots
When watering a sunflower in a pot, you should still follow the basic guidelines we mentioned earlier about how much water a sunflower needs. The main difference however will be ensuring that the pot does not become waterlogged or retain too much moisture. Also potted plants generally need to be watered more often than those in a garden plot or raised bed.
Gardeners should be especially aware of the dangers of overwatering sunflowers if they are growing their plants in a container. Even if you are watering your sunflower appropriately, if your pot or container doesn’t have proper drainage you could end up waterlogging and killing your plants.
The container that you use should have adequate drainage to allow excess water to freely exit at the bottom. You will also want to water more or less frequently depending on the water-retention properties of the soil that you choose to pot with.
Water on the florets and stem can cause water damage and promote growing conditions for bacteria and fungi which lead to disease so just water at the base of the plant.
Tips for Watering Sunflowers
- Monitor and water sunflowers most frequently during their flowering stage, roughly from day 45-85.
- If you live in a hot or arid climate, you may need to increase the frequency of your watering. Likewise, if you live in a rainy or humid climate, you can dial back the watering and let nature take care of some of the work for you.
- When growing sunflowers in pots, ensure that your container has adequate drainage at the bottom so that water can freely exit the pot.
- Aim for the base of the sunflower when watering- you don’t want to soak the head, leaves or stem of your plant.
- Sunflower roots grow deep into the ground- ensure that you have adequate space in your garden or pot, and make sure you provide enough water to reach all the way to the bottom of the plant’s roots. For containers always water through so that water drains out of the bottom.
- Water during the early morning is the best time to water followed by the early evening. Watering during midday leads to water evaporation in the air and from the topsoil and watering late at night can lead to disease if the plants foliage doesn’t dry off and stays wet through the night.
Please comment below with your own watering tips and routines!