Sunflowers are a beautiful addition to any garden, and they grow best in soil rich in organic matter to support their tall growth and (potentially) mammoth flowerheads. But if your garden’s soil isn’t ideal for sunflowers, don’t despair — with a bit of extra care, you can grow healthy sunflowers in almost any type of soil.
Sunflowers thrive in well-draining, loamy soil with a pH between 6.5 and 7.5. They have a large taproot and therefore prefer soil that isn’t too compacted so that the taproot has room to penetrate the soil. Any all-purpose potting mix will perform well for sunflowers in a container or raised bed.
I’ll go over the best soil composition for growing sunflowers, how to maintain good soil moisture levels, and how to properly fertilize your sunflowers.
The best soil for healthy sunflowers
Here are some factors to consider when choosing the best soil for your sunflowers:
- Sunflowers are heavy feeders. They need lots of nutrients to produce their large flowers.
- Sunflowers have deep roots, so they need loose and well-draining soil.
- Sunflowers prefer a neutral pH of 6.5-7.5 (on a scale of 0-14).
The ideal type of soil for sunflowers is loamy soil. This soil is a mix of clay, sand, and organic matter, and it holds just the right amount of moisture to support sunflower growth. Loamy soil is also easy to work with, so it’s a good choice for gardeners of all experience levels and almost all plants, not just sunflowers.
In a later paragraph, I’ll give a little more information about why loam is perfect for the garden and an overview of soil pH.
If the native soil in your garden isn’t loam, don’t worry. Sunflowers tolerate different soil types, as long as the ground is well-draining. That means almost any type of soil will work for sunflowers, as long as you amend it with some organic matter to help retain moisture.
The best soil for sunflowers in raised beds or containers
If you’re working with a smaller garden space or worried about the fertility and composition of your soil, growing your sunflowers in raised beds or containers is the way to go.
When it comes to filling your beds or containers, you have a lot of options in terms of soil. Walk into any hardware store, and it’s easy to get overwhelmed by all of the choices. Luckily, sunflowers aren’t picky.
Any all-purpose potting soil is great for sunflowers. But, if you’re looking for a recommendation, I like using FoxFarm Potting Soil for my potted flowers.
If you’re unsure how much soil you need for your raised beds, you can use this raised bed soil calculator to figure it out. It will tell you how many bags you need to buy based on the dimensions of your beds.
How deep the pot or container is is almost more important than what potting soil you buy. As mentioned, sunflowers have a large taproot, so they need a deep pot to anchor themselves securely. Although some flowers can be grown in shallow pots, sunflowers aren’t one of them!
Understanding soil composition
Knowing just a bit about soil’s general composition will help you better understand how this plays a role in the growth of your sunflowers.
Soil consists of three different-sized particles: sand, silt, and clay. Sand is the largest of these three particles, clay is the smallest, and silt falls in the middle.
The soil composition in your yard or garden will vary based on your region. If you live in the southern US, you might find that your soil is heavier on the clay side, while those who live closer to the coasts will find higher contents of sand in their soil.
You want your soil to have a good mix of sand, silt, and clay for growing plants. This composition is called loam, providing the best conditions for most plants. Too much clay, and your soil may be too compacted. Too much sand and the soil can’t retain any water or nutrients.
Soil pH tells you the acidity or alkalinity of your soil on a scale of 1 to 14, 1 being the most acidic and 14 being the most alkaline or basic.
Most plants prefer soil with a pH of around 7, which is the most neutral. But some plants like more acidity or alkalinity. Perhaps you’ve heard of blueberries needing acidic soil or that you can change the color of your hydrangea flowers by altering the pH of the earth.
To determine your soil’s pH, pick up a basic pH testing kit at your local garden or farm store. You can also complete a soil test through your local agricultural extension agency.
If your soil is too acidic or alkaline, you can amend it to make it more neutral. To lower the pH of your soil (make it more acidic), you can add sulfur to the soil. To raise the pH of your soil (make it more alkaline), add lime.
Here are a couple of my favorite products for amending the soil for my flowers. A little soil love will go a long way for more blooms.
My favorite garden soil supplies
When you know what condition your soil is in, it’s much easier to add anything that’s missing before your plants start to suffer. Find out your soil’s pH and macronutrient levels with an easy Soil Test Kit. Even without a soil test, worm castings are a safe bet to add to any garden, and your plants will love them. Wiggle Worm Soil Builder is a high-quality amendment that I add to all my garden beds that need a boost. Finally, learn why I don’t till my garden anymore with the “godfather” of no-till, Charles Dowding’s No Dig Gardening.
How to properly fertilize your sunflowers
If, after you’ve done a soil test, you find that your soil lacks fertility or a specific nutrient, adding fertilizer to your sunflowers can help with that.
Adding a slow-release granular fertilizer to your soil is a convenient way to round out the fertility of your soil and help your sunflowers grow well all season.
A slow-release fertilizer releases nutrients over a long period instead of all at once. They’re generally easier to work into the soil, and the nutrients are less likely to be lost due to soil leaching. An all-purpose fertilizer is like you taking a multi-vitamin. It has a little bit of everything but not too much of any one thing.
You can spread the granular fertilizer by hand at the base of your sunflowers. Make sure to incorporate it gently into the soil, then water it in, as this is what activates the fertilizer. If you see any fertilizer on the leaves of the sunflowers, brush it off as this can burn the plant.
It’s also crucial to read the label of whatever fertilizer you’re using to make sure you are using the right amount for your flowers.
Watering your sunflowers
Something else that’s important for healthy sunflower growth is maintaining good moisture levels in the soil.
As I mentioned earlier, sunflowers are somewhat drought tolerant, but only once they’ve established themselves. Water them daily to maintain good soil moisture for young sunflower seedlings. Once they have some good, sturdy roots developed, you can ease up and water them every few days.
If you’re unsure of the moisture content in your soil, don’t be afraid to get your hands dirty and feel the earth. I like to poke my fingers in the soil about two inches to check how it feels.
The soil shouldn’t feel soaking wet. Waterlogged soil will lead to root rot, and bone-dry dirt will stunt growth and perhaps kill young plants. Consistently moist soil is best for sunflowers (and almost all other garden plants, too!).
Keep a closer eye on the moisture level in your raised beds or containers. The soil in any kind of container tends to dry out more quickly than soil directly in the ground.
The air circulating over the top and sides and the lower volume of soil in a container contribute to quicker water evaporation. You may have to water your container-grown sunflowers daily during hot, dry weather.
Water at the base of the sunflower plant rather than overhead to help reduce the chances of fungal diseases developing on the leaves.
Maintaining soil moisture
One of the best ways to keep the moisture in your soil is to mulch. My preferred method of mulch is to use straw or wood chips, but you can use other things you may have available, like grass clippings, dead leaves, or wood chips.
Spread the mulch about 2 to 3 inches thick all around the base of your sunflowers. Just be careful not to bury the stem in the mulch, as this can cause the stem to rot from excess moisture. You want the moisture to stay in the soil, not on the sunflower itself!
Sunflowers as cover crops
One last thing I’ll mention that’s incredible about sunflowers is that they can be planted as a cover crop.
You read that right! Because of their deep taproot, sunflowers can bring up nutrients from deep in the soil and make them more readily available closer to the surface.
And remember what I mentioned at the beginning of the article about sunflowers growing in tougher soil? Their taproot can penetrate and break up soil that may be too compacted for plants with a more fibrous root system.
When you get ready to plant something else in the old sunflower bed, your past sunflowers will have done a lot of the soil prep for you. Pretty cool, right?
Having good soil is the first step to guaranteeing a robust sunflower harvest. Your sunflowers will do fabulous this year if your soil has a loamy composition, the proper nutrients, and is well draining.
If you’re starting with poor soil, give sunflowers a try anyway. If you take care to amend the soil and provide the right growing conditions, your sunflowers will reward you with beautiful blooms all summer long. Chances are, they’ll help improve your soil along the way.
And don’t forget to give a sunflower to someone you love to put a smile on their face. It definitely makes the hard work of gardening worth it.