Stellar Pink dogwood
Several years ago after planting a Rutgers Hybrid Stellar Pink dogwood, we had one of the hottest, driest summers on record. Despite having been planted the previous October, the tree struggled and drooped. Gallon after gallon of water was poured around the base but to seemingly no avail. Frustrated and worried I was going to lose an expensive tree, I headed to the US Botanic Gardens in DC to query the horticulturalists.
By 9 am the city was already steamy. Hot and cranky, the lone horticulturalist eyed me warily. Keeping my distance, I asked her opinion about dogwoods. She rolled her eyes. What about heat stressed dogwoods? Any advice? Perhaps debating between blasting me with the hose or parting with a wee bit of wisdom, she shot me a "Go away!" look and hissed that if I mixed 1 cup of Epsom salt with 5 gallons of water and poured it around the base every three weeks, my tree would recover. Grateful for the advice and worried about her grip on the hose, I thanked her and left. As quickly as possible.
Did it work?? Oh yeah!!! I added some liquid kelp meal to the mix and my tree recovered beautifully. Last summer when I made another annual pilgrimage to the US Botanic Gardens, the horticulturalist I talked to was kind and helpful. Maybe it was because I didn't ask about dogwoods....
Epsom salts aren't really salts at all but a form of magnesium sulfate. Both magnesium sulfate and liquid kelp meal have been proven to help plants resist environmental stress, including heat and drought related stress. Kelp also has the benefit of increasing the frost tolerance of a plant. Both provide vitamins and micronutrients to plants. My dogwood is healthy and I've already started pouring this mixture as a drench around the base of several plants that are currently struggling in my garden, including my roses that are battling black spot, an unhappy pipevine, and a patch of hot, thirsty day lilies.
How much kelp meal do I add? I pour in several big glugs, which probably equals about 1/2 a cup into my watering can, which holds four gallons. Make sure the salts have dissolved before you start pouring. You'll see the difference within a few days. Your plants will be happier, healthier, and better able to endure the rest of summer.
Last fall I moved this Night Owl climbing rose from a very moist, but too-shady spot to a sunnier spot. It leafed out and bloomed beautifully this spring, but has been miserable in our more-humid-than-monkeys-underwear 100+ degree weather. Along with removing its black spot infected leaves and spraying it with an organic fungicide, I gave it a drench of Epsom salts and kelp. It's already starting to perk up.