Rhubarb is one of the most productive perennial vegetables for home gardens. Like asparagus, it enters dormancy during winter before sprouting fresh growth in the spring. Because of its perennial nature, the veggie needs a proper growing location to thrive. A healthy garden is imperative for harvesting success!

Improper growing conditions, like soggy soil or excessive heat, can cause brown leaves. Rhubarb plants struggle to grow and photosynthesize, and their leaves turn brown over time. Abiotic factors, like herbicide usage or too much fertilizer, also cause browning leaves.

The Long Answer

Why rhubarb struggles depends on where it’s growing, the local climate, and how you treat it. Dry, hot regions will have different common problems than cold, frigid states with frosty winters. Consider your garden, the climate, and what rhubarb prefers to identify the issue. 

Soggy Soil

Wet, water-logged dirt is difficult for most plants to grow in. The airless soil drowns plant roots, preventing them from respiring and taking up water. After a few weeks of sitting in swamp-like conditions, the stems and leaves go limp and turn yellow, brown, or black. Unable to photosynthesize, they wither and die.

Prevent soggy conditions and brown, dying leaves by growing rhubarb in well-drained soil. A loamy mix is best, with equal parts sand, silt, and clay. If a site has too much clay or silt, consider amending the site with compost to improve drainage and water retention. Compost decays over time, adding structure and nutrients to poor soils.

Soggy soil is particularly troublesome in containers, planters, and raised beds. Use a well-draining potting mix, and cover the surface of the mix with compost or leaf mold—the mulches continue improving the soil throughout the growing season. 

Dry Soil

Similarly to wet soils, dry ones cause browning foliage. Instead of wet, withering leaves, those on plants in dry soils will be wrinkly and crunchy. They’ll easily break apart. Sites with lots of sand are typically prone to dry conditions, as water drains quickly from sandy earth. 

The fix for dry soils is the same as for wet ones: apply compost! Add a layer two to three inches thick onto the surface, and water it in well. Organic amendments like compost are some of the best things you can add to your garden. 

In moist climates with frequent rainfall, dry soils may be preferable! Aim for free-draining soils in wet areas and moisture-retentive ones in dry regions. 

Root Rot

Root rots often afflict rhubarb growing in wet sites, leading to brown leaves aboveground and mushy roots below. The fungi and bacteria that cause root rots thrive in warm, moist conditions. They’ll creep into your plants through wounds, pest entry sites, and broken roots. The plants struggle to grow after root rot begins, and their leaves shift from green to yellow, black, and brown.

Prevent root rots by growing rhubarb in rich, fertile, but well-draining soil. Use a potting mix with perlite, vermiculite, or pumice for container specimens, and amend in-ground beds with compost to improve them. 

If new growth doesn’t sprout after a while, the rot will have succeeded in killing your plant. Consider planting a new specimen in a different area with good drainage, plenty of nutrients, and full sun. 

Crown Rot

Crown rots are similar to root rots; instead of infecting the fibrous, feeder roots, they infect the rhizomatous crowns. Red leaf is a bacterial crown rot that commonly infects plants of the Pacific Northwest. You’ll notice brown, mushy portions of the rhizomes near the soil surface.

As time passes, the rot spreads throughout the plant. It’ll cause symptoms in the leaves and downwards in the roots. When you notice browning foliage, the rot may already be present throughout the plant. 

Always plant this veggie in well-drained soil, and avoid overwatering to discourage these rots from occurring. If crown rots are present, plant new crowns or seedlings in a different location for a few years to starve the disease. 

Leaf Diseases

Leaf spots, often from bacteria, can cause brown patches, streaks, and spots on tender leaves. Though rare, fungal powdery and downy mildews may cause brown patches in severe, prolonged infections. They’re gray, white, or black and fuzzy at first, and they cause yellowing and browning over time. 

Prevent leaf diseases by planting rhubarb plants with enough space. Proper spacing promotes regular airflow. Grant each specimen three to four feet from other plants, and maintain a weed-free bed.

Most leaf diseases aren’t fatal, and the plants often rebound from infections as the seasons progress. Some diseases are common during certain seasons; they’ll disappear after the season ends. 

Excess Fertilizer

Synthetic fertilizers are salt-based for instant release. In heavy doses, salts may accumulate in the ground and cause adverse effects on your rhubarb. The earth struggles to dissolve the nutrients, and they sit on the roots of your crops. 

In other cases, synthetic or organic fertilizers sit on the leaves. An accidental dusting can cause yellowing, browning, and necrosis, or cell death. 

The cure is simple: set a hose on low near the roots. Let it run for many hours to leach the salts out of the soil. If residue sits on a leaf or two, wash it off with a hose or watering can. If the damage is severe, chop off the dead leaves and wait for new ones to sprout. 

Pesticides and Herbicides

Similarly to fertilizers, pesticides and herbicides can waft onto tender rhubarb leaves and cause yellowing, browning, and blackening. If you don’t use chemicals but your neighbor does, they may waft over from their yard and into yours on windy days.

Pesticide and herbicide damage occurs quickly and all at once. Unlike diseases, the dead patches won’t spread or grow. They often occur in recognizable patterns that resemble droplets, splotches, and streaks. They’ll turn crinkly and brittle as the sun heats and dries the affected portions. 

Prevent herbicide and pesticide damage by avoiding the two chemicals. If you must use them, apply them in the morning or afternoon on mild days without significant wind flow. 

Pests

A few pests could cause browning in severe infestations. Rhubarb curculios are beetles that munch on the leaves, while stem borers creep into the stems and rhizomes. Large populations of these pests can harm your plant’s health, causing browning symptoms on the stems and foliage. 

Prevent pests by removing their hosts—they rely on docks, sunflowers, and thistles, as well as rhubarb, to survive year to year. Remove the weeds and you’ll prevent the beetles and tunneling borers from overwintering. 

If you see the adult beetles, pick them off and throw them in a bucket with soapy water. Keep them off your plants with row cover or greenhouse plastic.