Growing Rhubarb: Why Isn’t It Red?

Many gardeners have a problem growing rhubarb that turns red. We always assume the trouble is the kind of rhubarb we planted. Mine was inherited. It came with the house. The promisingly pink immature stems are bronze-kissed green by the cutting stage! Asking my mom what was up with my bronze rhubarb, I learned not all kinds are deep red. But Dad said, “You gotta grow the old varieties… the kind that a single stem fills a pie.” Apparently, everyone (including my grandmother) had that kind in the mists of time.

Okay, so the trick is buying heirloom rhubarb plants. But in the process of searching for the reddest of all heirloom rhubarb, I discovered that it’s probably not the plant at all, but where it’s planted and how it’s tended.

Growing rhubarb isn’t difficult.

Once established, these rugged perennials fend for themselves marvelously through too much rain, dry spells, and 40 below zero winters. Everyone lets their rhubarb do its own thing after planting. Which is exactly how we arrive at a less than stellar red harvest. You need to do a little maintenance – rhubarb’s own debris alters the stem color.

Rhubarb is naturally quite sour, which tells you that it is high in acid content – like lemons and limes. However, the plant prefers soil with 6.0-6.8 pH. And if you’re incorporating acidic organic material into good garden soil, it will reduce the pH. (Which is why you shouldn’t put citrus in the compost pile!)

Some plants are very sensitive to soil pH, like getting blue hydrangeas to give you blue flowers. They may grow just fine when the preferred pH is off, but it messes up the color. And so it is with growing rhubarb.

The key to red rhubarb?

Cutting the plant back to the ground in fall and removing the clippings from the area. However, what is the natural pH of your soil? That is, before rhubarb leaves started changing it when left to decompose at its base every autumn? Chances are that if other garden plants aren’t exhibiting signs of pH trouble, your soil is fine elsewhere, so transplanting the rhubarb to a new location will fix the issue with the next harvest. Then you can amend the soil to correct the pH issue before putting another plant in that spot.

The best time to move rhubarb is in the fall or spring, but if you’re going to divide it while you’ve got it above ground, wait until early spring, right after the ground has thawed. Fall divisions won’t kill the plant, but you might not get budding points in every chunk of the old root ball. And it should be divided every 10 years.

Of course, you could also leave the rhubarb where it is and correct the pH. That is – as long as the plants are in full sun all day. Sun is also important to getting rich color.

The fastest way to raise soil pH organically is to scratch in some hardwood ashes and water in deeply, but the effect is short-lived. Crushed eggshells give you a longer soil sweetening resource, and oyster shells work too with an even longer effective time span. But if the soil pH dropped from growing rhubarb without removing its debris, then perhaps a shot of ash and some eggshells are all you need to turn your rhubarb red again. It might become something you need to do each fall or spring, depending on your average natural soil pH.

By the way, I suspect that the secret to growing rhubarb stalks big enough that just one will make a pie is composted cow manure. Grandma isn’t around anymore to check my theory, but I’m pretty sure their slim budget and the Great Depression meant using free fertilizer sourced from her father-in-law’s barn. Because the rhubarb patch I remember was nowhere near that lush, but it sure produced killer pies!