Make Yellow Leaves on Bottlebrush Green Again

Q. I love my lemon bottle brush shrubs, but the leaves started yellowing. l recently added five inches of organic top soil. Additionally, l think l should add acid. What kind of supplement should l use for a long-term solution?

This bottlebrush is yellowing because it surrounded by rock mulch and planted in native, desert soil.

A. Leaf yellowing can be caused by many different things. With bottlebrush, it is frequently a shortage of available iron to new growth. More importantly, the soil is collapsing resulting in poor drainage and not enough air reaching the roots.

            I see this often when any bottlebrush is surrounded by rock mulch. Over time, the soil around the roots becomes mineralized. In my opinion, all bottlebrush plants, in general, should not be surrounded with rock covering the soil.

This is an example of an iron fertilizer that dissolves in water that can be sprayed on plants with yellow leaves.

            Once leaf yellowing due to a shortage of available iron, it cannot be reversed quickly by adding soil amendments. The most immediate color leaf reversal would be spraying the leaves multiple times, a few days apart, with an iron solution. But the yellowing will return to new growth as the iron runs out.

            Adding an iron fertilizer to the soil, such as an iron chelate, lasts longer, up to about 1 year. It is added in early spring, about now. But the next year you need to add more iron chelate to the soil, before new growth begins.

This is also an iron fertilizer but the iron is added as the chelate with the acronym or nickname EDDHA. This particular chelate holds on to iron regardless of the alkalinity or pH of the soil. This is not true of other iron chelates.

            But when iron is added to the soil, the leaves which are yellow remain yellow. Green leaf color only occurs in new growth which hides the yellow leaves until they drop off. To turn yellow leaves green again requires a spraying the plant with the iron solution I mentioned earlier.

            For the long-term, you must improve the soil where the plant is growing so that the alkalinity of the soil is reduced, and the roots have better access to air. This can be done by adding compost to a soil that has become mineralized and covering the soil with wood chips rather than rock.

This is a compost made from municipal solid waste. The compost is made from waste products from the city and includes human waste or biosolids that has been composted. All compost from municipal solid waste must meet EPA's health requirements before it can be sold to the public.

            When preparing a spray solution that contains iron, follow the label directions. But I suggest using either distilled or reverse osmosis water rather than tap water. This is because of the alkalinity in our tap water. In distilled or RO (reverse osmosis) water this alkalinity is removed. I am concerned that the alkalinity in tapwater might interfere with the effectiveness of your iron sprays.

            I would also include something to make the spray solution “wetter”. In a pinch you can use a liquid dishwashing detergent but it’s not ideal since it contains so many additives such as hand lotions and perfumes. It’s better to use a liquid detergent which is purer such as Dr. Bonners or a detergent made from Castile soap.

This is a liquid detergent, aka surfactant, that I use and purchase online. Notice that it is unscented and it is also certified as organic through Oregon Tilth.

This is another surfactant that I like which is made out of saponins or agave extract that can assist fertilizers dissolved in water to move inside the leaf through the surface.

            Both the purified water and liquid detergent is important because it helps move the iron contained in the solution through the leaf surface and inside the leaf .

            Spray the leaves long enough so that the spray solution begins running off its surface. Spray both the upper and lower surfaces of leaves so that the sprayer is taken inside the plant more effectively.