How and When to Fertilize Your Annual Containers for Robust Blooms
Are your potted plants looking a little less robust than you were hoping for? They might need some fertilizer! Join gardening expert Melissa Strauss in discussing when and how to fertilize your annual containers.
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Freshening up my annual containers is one of my favorite garden tasks. These potted plants add so much color and vibrancy to our outdoor living spaces. If you want to keep those stunning annuals popping all season, knowing how and when to fertilize them is important.
Even though they are short-lived, annual plants still benefit from added nutrients. But, before you jump in and start feeding them, there are a few factors to consider. Fertilizing too much or too often can cause problems in their own right.
Experts agree that fertilizing your annual containers is an important step in caring for them. Frequent watering can wash away the nutrients in the soil, and it’s imperative to their health that we replace them. Let’s take a look at the best way to add those nutrients back in and keep your potted annuals looking their best throughout the season.
Step 1: Start Strong
I’d like to start at the beginning, which is preparing to plant. The type of container you choose, as well as your soil, both play a role in the availability of nutrients for your annuals. It’s important to freshen up your soil each year before you re-fill those pots.
I know that changing out all the soil in a raised bed or other sizeable container every year is a big ask. For these larger planters, you don’t need to empty and re-fill, but you do need to replenish the nutrients.
Over time, the soil in those containers can settle and compact. The nutrients in the soil get used up, and you end up with soil that won’t support healthy growth. Topdressing these with some compost or fresh garden soil will help to freshen them up.
Another option for larger containers is to plant a cover crop during the off-season. Cover crops aren’t just for farmers, they can help give that old dirt a facelift. Adding a layer of mulch around your annuals will help to enrich the soil over time, as well.
For smaller pots, it’s best to change out the potting mix every year. Some potting soil already has some fertilizer in the mix. This is intended to get you off to a strong start, but it won’t last all season.
If your potting mix doesn’t contain fertilizer, it’s important to add some before you add those annuals. You can beef up your mix with some well-rotted compost or worm castings. Alternatively, add a slow-release formula for that initial feeding.
Step 2: Devise a Plan (and Write it Down!)
This may seem like a no-brainer, but I am personally guilty of irresponsible and unscheduled fertilizing. It’s not a big deal if you do it slightly less often than recommended. However, overfertilizing is a killer, literally.
Too much fertilizer can burn the roots, and ultimately, kill the plant. A buildup of salts will cause root damage that inhibits the intake of water. Overdoing it can make them more susceptible to pests and diseases and decrease their drought tolerance.
So what is the solution? It’s simple, really, almost too simple. Just write it down. Mark an “F” or some other indication on your calendar on the day you fertilize. Don’t re-apply without checking to see if it’s time.
Step 3: Choose the Right Formula
When selecting a fertilizer, you can go as simple or complicated as you have the time for. I like to use a bloom-boosting formula for my flowering plants. This isn’t desirable for herbs like basil because blooming alters the flavor in a bad way.
If you prefer a one-size-fits-all solution, an all-purpose formula will work just fine. That’s why it’s called all-purpose! A balanced ratio of nutrients works for most annuals.
When I say a balanced ratio, I’m referring to the amount of three macronutrients that make up most commercial fertilizers. These are, in order, nitrogen (N), phosphorus (P), and potassium (K). A balanced formula will have a ratio of 1-1-1 or any combination of the same three numbers. Many all-purpose fertilizers also contain other important nutrients like zinc, iron, and manganese.
You’ll also need to choose between soluble or slow-release formulas. Soluble formulas dissolve in water and feed the plant immediately. As you might expect, slow-release formulas deliver nutrients more slowly over an extended time.
Slow-release fertilizer is great for most annual containers. They reduce the risk of fertilizer burn and deliver a more controlled amount over time. Larger plants may benefit from a soluble formula and more frequent application. Just be careful to read the instructions and don’t overdo it.
Step 4: Read the Instructions
I want to drive this point home, but I’ll be brief about it. It’s important to read the instructions on your chosen fertilizer. This will tell you how to apply it, whether to dilute it, and how often to use it. It’s better to be slightly conservative in your application than to go overboard.
If you prefer to fertilize more frequently than your product recommends, make sure to dilute it appropriately. If your instructions say to dilute by half and apply monthly, you can also dilute by a ratio of 4:1 and use it bi-weekly.
Step 5: Give Plants a Drink Ahead of Time
When fertilizing day rolls around, there is one more important step to factor in. It’s important to irrigate your plants before you apply fertilizer. It’s a good idea to make sure you water the day before fertilizing day, to allow plants time to hydrate thoroughly.
Irrigating ahead of fertilizing serves two purposes; it allows the plant to absorb the fertilizer more efficiently, and it helps to prevent root burn. Moist roots are better at absorbing nutrients, so it doesn’t just build up.
If you live in a hot climate, like I do, you probably irrigate your plants daily in the summer. Here in Zone 9, watering the potted plants is a daily chore, and when I skip it, it shows. In this case, water all of your plants the day before and then again the day of if the soil is dry. Then, go back and apply your fertilizer to the moist soil.
Step 6: Time it Correctly
Just as you should water in the morning, you should also fertilize in the morning. The reason for this is both simple and nuanced. To put it plainly, if you water and fertilize in the morning, the plant has a better chance of absorbing the water and nutrients.
The sun causes moisture to evaporate. If you water later in the day, your plants don’t have the same opportunity to absorb that moisture. This is especially true if you are using a soluble fertilizer. The fertilizer solution will evaporate quickly, just as plain water will.
When you fertilize in the morning, the air and soil are still cool. This allows the plant time to absorb the moisture it needs before the sun evaporates it.
You might be wondering if it’s also ok to fertilize in the evening. Temperatures go back down and the sun is no longer so intense in the evening. It seems reasonable that this would be a satisfactory time to irrigate and fertilize.
Evening is not the best time to water or fertilize, and here is why. When you water in the evening, the soil and plants stay wet overnight. There is no opportunity for the sun to evaporate the moisture at all. This can lead to fungal issues. However, it’s totally ok to water in the evening in a pinch.
Step 7: Repeat at the Proper Intervals
The final piece of the fertilizing puzzle is repetition. Annuals are usually heavy feeders, so they will tolerate frequent fertilizing. As always, it’s a good idea to follow the instructions on your fertilizer package.
That said, it’s typically good to fertilize your annual containers once every one to two weeks. Because you’ll need to water these containers often, you wash away the nutrients in the soil. Replenish them often, but make sure to dilute your fertilizer as instructed.
What If I Accidentally Overdo it?
If you’ve accidentally over-fertilized your plants, there are important actions to take to fix it. Over-fertilized plants will show signs of salt burn, such as dry or burned leaves, particularly around the edges. Some older leaves may display a white, crusty buildup.
If you are concerned that you have made this mistake, the best solution is to re-pot the plant. In less severe cases, you may be able to flush the container with water. In advanced cases, remove it from its container, rinse the roots, and re-pot with fresh soil.
