Can foliar sprays fix magnesium deficiency alone?
Written by
Liu Xiaohui
Reviewed by
Prof. Martin Thorne, Ph.D.Foliar sprays provide a rapid solution for plants exhibiting magnesium deficiency symptoms, but cannot remedy magnesium deficiencies alone. Foliar sprays contribute to less than 20% of a plant's total magnesium needs because of limited uptake through the leaves. The condition of the sprayer solution only lasts a few hours (the breakdown process starts almost immediately during photosynthesis, especially if it's sunny). Sorely deficient symptoms may be temporarily masked, but this is only hiding soil deficiencies. I have witnessed "relapses" of magnesium deficiency symptoms in plants in my care that were foliar-sprayed weeks later, without any soil amendments.
Absorption Constraints
- Leaf cuticles limit magnesium penetration
- Maximum 15-20% absorption efficiency
- Rain or irrigation washes off solutions quickly
- High temperatures accelerate solution breakdown
Temporary Relief Only
- Symptoms improve for 5-7 days after application
- Does not replenish magnesium reserves in roots
- New growth shows deficiency again rapidly
- Photosynthesis rates drop after spray effects fade
Supplemental Role
- Best used while waiting for soil amendments to work
- Effective during critical growth stages like flowering
- Cannot replace soil magnesium bank for fruiting plants
- Requires repeated applications increasing labor costs
By using foliar sprays and soil amendments, you achieve better long-term results. I would apply foliar solutions, such as organic fertilizer, in the early morning while stomates are open, as a complement to any soil corrections you might use, including dolomitic lime or compost (or both). I use a schedule of foliar spray applications every 10 days while the slow-release amendments are breaking down. In this way, you are filling the gap of not being able to utilize amendments. At the same time, the foliar sprays help with recovery.
Root absorption remains crucial for complete recovery in these cases. More than 80% of magnesium will enter through root hairs from the soil solution. This mineral will reserve itself with reserves found to support the entire period of growth. Foliar sprays help redistribute existing magnesium only temporarily. Ultimately, my soil tests indicate that there is no lasting increase in magnesium from foliar-only programs.
Use balanced programs mixing both practices every season. A 2% foliar magnesium sulfate solution should be sprayed during critical growth stages. Dolomite or compost should be used annually to replenish the soil's inputs. The nutrient value of magnesium in new growth should be assessed for a true indication of recovery; the greener the colour, the more positive the growth. A combined strategy will ensure that your plants are healthy and productive from season to season.
Read the full article: 7 Critical Signs of Magnesium Deficiency Plants
