Lupin Leaves Turning Red [And What to do now]

If you grow lupins, you probably love them for their colorful flowers, soil-enriching capacity, and ability to attract bees. Given these (and the fact that growing lupins in places like California and Oregon can be expensive), you want to keep them as healthy as possible. So it’s only natural to worry when your lupin’s leaves suddenly turn red.

If your lupin leaves turn red, your plant may be gradually dying. Perhaps your garden does not have the necessary conditions to support the lupins, or the plants have been exposed to harmful elements. Whichever the case, it is crucial to take the necessary steps before you lose your garden lupins.

The rest of this article will shed more light on why lupin leaves turn red and what to do when you notice a sudden color change. I’ll also explore ways to lower soil phosphorus levels to prevent your garden lupin leaves from turning red.

Table of Contents

Why Do Lupin Leaves Turn Red?

You may be fond of the color red, but if it appears on the leaves of your garden’s lupins, that’s not a good sign.

Lupin leaves turn red because the plant was exposed to harmful conditions such as unfavorable pH levels due to high amounts of phosphorus. Left unchecked, the red leaves may start to wilt and signal the death of your precious plant.

Let’s further discuss the conditions that cause lupin leaves to turn red.

Your Garden Has Too Much Manure

Generally, manure helps to improve soil drainage and gives plants the nutrients they need for healthy growth. However, too much manure can harm your garden plants, especially if you grow lupins. While most plants thrive when manure is added to the soil, lupins can grow on little to no manure.

See, manure increases the soil’s pH levels which in turn causes the leaves to turn red. If you’ve recently applied manure to your garden and the lupin leaves turn red, that’s the likely cause of the issue.

Your Soil Is Too Rich

A soil is “rich” when it has high levels of nutrients. Although rich soils generally promote the growth of most plants, lupins are an unfortunate exception to this rule. That’s because lupins thrive in soils that have low nutrient and pH levels.

If your lupins get more nutrients than they require, their chlorophyll gets replaced by red pigments, which slowly turn the leaves red.

Eventually, the lack of chlorophyll prevents the lupin leaves from undergoing vital processes such as photosynthesis, causing them to die.

What Should I Do When Lupin Leaves Turn Red?

When lupin leaves turn red, you must take action as soon as possible. You need to get rid of excess manure, replace the soil, or move the plants to an area that is more favorable for healthy growth.

Below are the specifics on what to do when your lupin leaves turn red and how to save your plant before it’s too late.

Get Rid of Excess Manure

Excessive application of manure is a common cause of red pigmentation on lupin leaves. If you’ve recently applied manure around your plant and its leaves start turning red, a simple solution is to get rid of any unnecessary manure.

Gently scoop out the manure around your plant using a trowel and relocate it to other parts of the garden.

I suggest using the Edward Tools Garden Trowel (available on Amazon.com) for this, as the trowel won’t rust even if you use it to remove manure on a regular basis. It also has an ergonomic handle so your digging hand won’t suffer under the weight of too much manure.

Once the manure around your lupin is removed, your plant should slowly recover (assuming the manure is the root cause of the problem).

Replace the Soil

Red lupin leaves usually indicate that the soil around your plant has nutrient or pH levels that aren’t conducive to the plant’s growth. Lupins cannot thrive on pH levels higher than 4.0.

If you want to measure the pH levels of your lupins’ soil, I recommend the SONKIR Soil pH Meter, MS02 3-in-1 Soil Moisture/Light/pH Tester (available on Amazon.com). Not only does it measure pH levels, but it also tells you how much sunlight and moisture your plants are taking in.

If your soil is too rich, you may need to replace it with one that has lower pH and nutrient levels. Doing this may lessen the likelihood of your lupins’ leaves dying and increase your plant’s chances of survival.

Move the Plants

If you’ve recently planted your lupins and their leaves start turning red, you can always move them to a new location with more favorable conditions. However, note that this solution works best for newly planted lupins, as they’re only beginning to get used to their new soil.

Of course, the new soil should have lower pH and nutrient levels as I explained earlier. It should also be well-drained and in a partially-shaded area to ensure your lupins grow healthy.

As you know, excess soil moisture causes problems like root rot, which is the last thing you want to happen to your lupins (or any other plant for that matter).

Should I Cut My Lupins’ Leaves When They Turn Red?

You should cut your lupins’ leaves when they turn red. Pruning the leaves will allow you to monitor your lupins’ health since you can quickly spot any developing red pigmentation on them and zero in on any possible causes of the same.

Carefully snip off the red leaves at the base using a pair of pruning shears. I use the FELCO 068780 Classic Manual Hand Pruner (available on Amazon.com), which comes in a variety of styles. You can easily adjust these shears according to your needs, and there’s a lifetime warranty in case the blades sustain any covered damage.

Once the red leaves have been removed, your lupin leaves should grow back to their full green color under the right conditions.

However, if all of the leaves have already turned red, then it’s highly unlikely you can save your lupin. If you leave only a handful of leaves, they may not be enough to help absorb the nutrients your lupin needs.

How To Lower Phosphorus Levels in the Soil

Although phosphorus is one of the essential macronutrients that help plants grow healthy, excessive quantities of it can harm plants such as lupins. Therefore, you need to ensure that the phosphorus levels in your garden are within your lupins’ tolerable limits.

Unfortunately, there’s no quick way to reduce phosphorus levels that already exist in the soil. What you can do is limit the amount of phosphorus that gets introduced into your soil before it adversely affects your lupins.

Let’s look into some steps you can take to lower soil phosphorus levels in the soil and ensure the growth of healthier lupins.

Stop Applying Manure

Although many lupin growers use manure to naturally fertilize their plants, you don’t want to apply too much of it. Manure contains large amounts of phosphorus which alter your soil pH, resulting in (as I mentioned earlier) red leaves on your lupins.

If you’ve already applied manure to the soil where your lupins grow, you should stop any future applications. With time, the macronutrient levels should eventually subside, since your other plants will likely absorb the phosphorus that already exists in the soil.

If you must use manure to increase levels of other macronutrients like nitrogen, you should apply it less than annually. Better yet, you should only apply it based on how much nitrogen your plants need.

Grow Nitrogen-Fixing Plants

Planting nitrogen-fixing plants is an excellent way to increase vital macronutrients and moderate soil phosphorus levels at the same time.

As their name suggests, these plants release nitrogen into the soil as they use the existing soil phosphorus, keeping nutrient levels balanced.

Legumes such as beans and peas are perfect for fixing the nitrogen in your soil. However, planting these may not be effective if your soil nitrogen levels are deficient.

Before growing nitrogen-fixing plants, have a sample of your garden soil tested to know its exact nutrient composition.

Use Phosphorus-Free Fertilizer

If you want to fertilize your soil without increasing its phosphorus content, phosphorus-free fertilizers are a great alternative to manure.

However, the downside to these fertilizers is that they only contain nitrogen and potassium — meaning you have to double-check if there really is too much phosphorus in your soil before using phosphorus-free fertilizers. Otherwise, you may risk depriving your other plants of vital nutrients.

You can identify phosphorus-free fertilizers by the ‘0’ in the middle of the string of numbers that indicate their composition. I recommend LawnStar’s Balanced 15-0-15 Liquid Fertilizer (available on Amazon.com). It’s a phosphorus-free fertilizer fortified with other nutrients integral to plant health. It’s also highly water-soluble, making it easy to apply.

Final Thoughts

Lupin leaves turning red is a common issue encountered by those who grow the plant. The red pigmentation often indicates that your precious plants are exposed to unfavorable soil pH and nutrient levels. You can therefore rid your lupins of red leaves by changing the conditions in which they grow.