Many gardeners have trouble growing plants such as Calibrachoa and don’t know why they can’t grow them in containers. Here’s the deal to understand.
This plant is often described as a “high feed” or “high iron” plant and while they do love to be fed, and won’t produce well under low-feeding regimes, there are other factors at work.
Plants such as Calibrachoa lack the ability to take up iron under high-intensity cultivation – and this is particularly true when the soil media pH is too high.
In order to succeed then, you have to ensure the soil acidity stays acidic.
In order to succeed then, you have to ensure the soil acidity stays acidic. If you have high-alkaline water, you’re turning your soils alkaline with every watering. And thus making it hard for this particular plant to thrive.
In our greenhouses with our high-alkalinity, high-pH water, I had to add acid to the water in the propagation house to make sure I didn’t wreck the pH of the soil with these tender seedlings and cuttings. Once out in the nursery and garden, they were fine (for the most part).
Understand that plants in containers thrive on soils that are more acidic
Also, understand that plants in containers thrive on soils that are more acidic than the preferred soils in-ground culture. In other words, grow a bedding plant in a container and it wants more acidic soil than it does in the garden.
Iron deficiency symptoms
Iron deficiency symptoms include chlorosis (yellowing) of the younger leaves and mostly concentrated along the stem and lower section of the leaf next to the stem.
There is usually minor “netting” of the remaining green leaf surface. Note that once these start to happen (in even a barely noticeable way) the plant becomes susceptible to other issues such as moderate overwatering or root disease.
In other words, the iron deficiency reduces its ability to fight off minor stress.
The best pH is between 5.5 to 6.2 for Calibrachoa. On the whole, keeping pH around the 6.0 mark is the best plan.
If you see growing problems with this plant, then do check for soil pH first and if that’s fine, investigate further.
A regular soil test kit will give you “close-enough” data.
If pH is too high
If the soil pH is too high, then you have to acidify the soil and you can do this by adding acid to the irrigation water (vinegar works well on the home scale and you do have to test to bootstrap your way to a 5.5-6.0 water pH test ) or using an high-ammonium, acid-reaction fertilizer (such as 21-7-7 or 9-45-15) will drive the pH down. Adding an iron-drench to supersaturate the container soil is sometimes used as well.
Cool, humid and low-light conditions can make a small problem seem much worse.
So if you’re having problems growing this particular plant, or even trouble growing a great container plant, now you know how to go about it and produce a show garden.
One thought on “Why You Can’t Grow Calibrachoa and Other Plants in Containers”
Thanks for this information! I never thought about plants requiring iron, even before this garden.
My garden soil is acidic clay. My well water is high in dissolved iron (so we cannot drink it unfortunately) and so my plants in or out of pots don’t suffer iron deficiency. But the water ‘bronzes’ the leaves and stones etc which drives me mad. It isn’t filterable. So we live with orange stones and bronze plants!