Magnesium for Plants

In spring and summer, apply once weekly at 1-2 tsp per gallon, using a watering can or a hose-end sprayer on the 2 tsp setting. In fall and winter, cut back to every 4-8 weeks. Use it alongside your regular fertilizer, not instead of it, since it supplies magnesium rather than N-P-K. Treat when you see the telltale interveinal yellowing on older leaves, and continue while new growth greens up over the following weeks.

At 1 tsp per quart, the 8 oz bottle makes about 48 watering cans of feed. For a typical shelf of 10–15 plants fed every 1–2 weeks in season, that's several months of feeding — and the 32 oz bottle four times that.

The classic sign is yellowing between the veins on older, lower leaves while the veins themselves stay green — sometimes with leaf edges curling or turning reddish. It appears on old growth first because the plant moves magnesium to its new leaves when short. If instead the yellowing is on new growth, that points to iron; if whole leaves yellow uniformly, that's nitrogen. Matching the pattern and leaf age to the right nutrient saves you treating the wrong thing.

It's closely related — the magnesium in this product comes from magnesium sulfate, which is what Epsom salt is. The advantages here are a consistent, measured concentration and the added kelp for uptake, formulated as a plant supplement with clear rates. So it does the same core job of supplying magnesium and sulfur, in a form made for straightforward garden use. Either way, it's a genuine magnesium source, useful specifically when a magnesium shortfall is the actual problem.

Containers lose magnesium quickly, because frequent watering leaches it out of the limited soil, and potting mixes often start low in it. Heavy feeding, especially with high-potassium fertilizers, makes it worse, since potassium competes with magnesium for uptake. That combination means potted plants — and plants in sandy or acidic soils that hold magnesium poorly — show magnesium deficiency more often than those in rich garden beds. A magnesium supplement corrects the gap those conditions create.

New growth greens up over a couple of weeks once magnesium is available, and a foliar application can speed visible improvement. Existing yellowed leaves may partly recover but often won't fully re-green, since the damage is already done — so you're mainly feeding healthy new growth. For an ongoing tendency toward magnesium shortfall, like sandy soil or containers, steady use through the season keeps it from recurring.