What Would Turn My Asparagus Fern Yellow?

Water and Sun

• Although asparagus ferns are able to withstand drought due to enlarged underground water storage organs, they still can feel the sting if waterings have been scarce or irregular. Stick your finger in the soil of your plant regularly to check the moisture level -- if it feels dry to the second knuckle, you should water your asparagus fern thoroughly, until water runs out the drain holes in the pot.

  Lighting may also play havoc on the coloration of asparagus ferns. These plants are not true ferns, actually belonging to the lily family, and because of that require bright lighting to thrive. If your asparagus fern is tucked into a dark corner, provide supplemental light or move it close to a window that receives bright, indirect sunlight.

Seasonal Changes

• When planted outdoors, asparagus ferns respond to seasonal changes in their environment. These herbaceous perennials die back to the ground when nights get chilly, first turning yellow and then light brown before collapsing. Even indoor asparagus ferns are victims of time, though, and will often shed old stems slowly. These stems yellow just like they would from a seasonal dieback because the plant effectively cuts off all nutrients and water to old sections of growth. You can remove the yellowing areas with a pair of pruners to neaten the plant.

Asparagus Rust

• Asparagus rust is common when the weather is moist and cool -- standing water on ferns and temperatures between 68 and 72 degrees Fahrenheit are optimal conditions for germination. Early infections often appear as light green to yellow spots on shoots and stems, with rust-colored pustules following. The tops of plants may appear blackened toward the end of the growing season.

  Protect asparagus ferns from rust by watering them only near their bases, never on their needles, and thinning tightly spaced clumps for better air circulation. If rust is already present, you may want to spray the fern thoroughly with neem oil, mixed at a rate of 2 tablespoons per 1 gallon of water. Repeat this treatment weekly, until all signs of rust are gone.

Root Rot and Fusarium

• Asparagus ferns are particularly sensitive to over-watering and root and crown rots are common. Exacerbated by the soil-borne fungi Fusarium oxysporum f.sp. asparagi and Fusarium proliferatum, root and crown rots slowly kill plants by destroying the roots themselves. The Fusarium fungi goes in to finish the job by plugging transport tissues, effectively severing the plant from any roots that remain.

  Avoid root rot with careful watering, allowing houseplants to drain completely and never leaving them standing in a saucer full of water. Amending the soil of asparagus fern beds with compost can help improve drainage and protect roots in outdoor plantings. If you plants already are showing signs of root rot, such as stunted growth, yellowing ferns and generally looking unhealthy, you may be able to save them by digging them and trimming off any root sections that are black, brown or soft and replanting in well-draining soil.