Summer tonic for heat-stressed plants

Recently on GardenLine, guest experts Beverly Welch of the Arbor Gate and Angela Chandler of The Garden Academy discussed an old posting on the Arbor Gate blog that referenced a “summer tonic” for heat-stressed plants. They described it as a sort of “Gatorade” for plants, similar to the electrolyte replacement for humans sweating from summer heat. 

Angela wrote the piece for Beverly’s blog five years ago, noting that things can still go wrong even if you follow the standard plant-care practices we talk about on GardenLine.  That’s especially so with the exceptional heat and humidity we endure during our summers. 

Angela’s summer tonic is a combination of Epsom salt, liquid seaweed (kelp), and SuperThrive®.  She wrote …

Despite the name, Epsom salt is not a sodium salt like table salt, but rather a source of the minerals magnesium and sulfur. Gardeners have used Epsom salt for decades, and it has many uses in the garden. Magnesium plays a crucial role in photosynthesis – the process by which the plant converts light energy into chemical (food) energy. There are some exaggerated claims about Epsom salt out there. We can weed those out from its practical applications and use it in a common-sense way.

Seaweed (kelp) provides roughly 60 trace minerals plus amino acids and enzymes. It enhances root development, stimulates microbial activity, and promotes the production of auxins (natural plant growth hormones).  SUPERthrive® is a combination of vitamins and plant hormones. It is not a stand-alone fertilizer but can be added to fertilizers. It is well known to reduce transplant shock.

To read the whole article, see,  but here’s the quick formula: 

• 5 gallons of water

• ⅔ cup liquid seaweed

• ⅔ cup Epsom salt

• 1 tablespoon SUPERthrive®

The ⅔ cups are based on a recommended application rate of 2 tablespoons per gallon of water – ⅓ cup is 5⅓ tablespoons. If the products you use recommend more or less, adjust as required. You can substitute Garrett juice for the liquid seaweed, but you will need to increase the amount to 1¼ cup per 5 gallons. Garrett juice includes compost tea and horticultural molasses as well as seaweed. 

Water your plants thoroughly the day before application. Then apply the tonic as a drench, wetting the root zone of the plant. You will use ½ to 1 gallon for shrubs, and less for perennials, vegetables and bedding plants. It will take several days to see results. How often to apply depends on how stressed the plant is, how long the heat lasts, and the general health of the plant in the first place.  Container plants may benefit from using this tonic weekly, but if you choose to do this, dilute it by half with water. This follows the “weakly, weekly” practice and can keep easily stressed plants, like root-bound ferns, happy through the summer. 

With any supplement, there is a tendency to think that if a little is good, more is better. We have to remember, however, that any excess we apply can leach out of the soil and end up in the watershed. It is best to apply conservative solutions on a regular basis rather than a large amount all at once.

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