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No plant has lived up to its common name like the sweet pea. These adorable flowers have the best colors, are innocently delicate, and have the sweetest scents. They’re the perfect compliment to anything in your garden, but you need to know how to grow them to enjoy them to their full potential. A common question is whether or not sweet peas will grow in ericaceous compost.
Ericaceous compost is too acidic for sweet peas to grow. Sweet peas prefer neutral or slightly alkaline soil, but ericaceous compost attacks the roots of sweet peas, eventually killing them. The most acidic soil that sweet peas can take is 5.8, but ericaceous compost is often as low as 4.0 or 5.0.
If you would like to learn more about what ericaceous compost does to sweet peas, the pH limits of sweet peas, and the soil conditions they like the best, then keep reading.
Can Sweet Peas Grow in Ericaceous Compost?
Ericaceous Compost is a highly acidic soil mixture and is used for acid-loving plants such as blueberries, azaleas, and bunchberries.
So before you purchase a bag or make your own ericaceous mixture, you need to know if sweet peas even like acidic soil. The answer is they definitely do not.
Sweet peas actually like to grow in neutral or slightly alkaline soils, NOT acidic soil, like the ericaceous compost.
On a pH scale between 0-14, where anything above 7.0 is alkaline, and anything below 7.0 is acidic, sweet peas love soil with a pH level between 7.0-7.5.
Do all of the 110 varieties of sweet peas prefer alkaline soil? Absolutely! From the Air Warden sweet pea to the Crimson Apple sweet pea to the Turquoise Lagoon sweet pea, they all prefer to grow in the same kind of soil, which we’ll go into more detail about in the following sections.
Is it at all possible to grow sweet peas in ericaceous compost? Let’s take a look at why you shouldn’t bother in the next section, and you’ll see what I mean.
What Happens if I Grow Sweet Peas in Ericaceous Compost?
If you already have ericaceous compost, you might be thinking to yourself, “how bad could it be to grow sweet peas in my compost? Maybe it isn’t too acidic for it.”
Hold your horses, my planting trigger-happy friend!
Ericaceous compost is usually between 4.0 and 5.0 on a 0-14 pH scale, where 7.0 is neutral soil, which is MUCH more acidic than the peas can handle. They won’t die right away, but the issue is that the acidic soil will inhibit the good bacteria that live in the roots of the peas.
That bacteria lives in the nodules of the roots and are the sites of nitrogen fixation. If there’s too much nitrogen in the soil, which makes the soil acidic, the bacteria will consume it and neutralize the pH a little bit.
The bacteria will die if the soil is too acidic, with more acidic components than nitrogen. You may end up seeing the petals dropping off without a clear explanation as to why.
So what if you’ve already laid down the compost? Is all lost? Not at all! Sweet peas can withstand a slightly acidic solid of 6.5 or even 5.8 and be alright. The Spruce will recommend that you add compost to your existing soil if it’s poor and nutrient-deficient.
In the early stages of decomposition, compost will always be naturally slightly acidic so that some acidity won’t kill your sweet peas.
What soil will Sweet Peas Grow in?
So, if ericaceous compost doesn’t work for sweet peas, what should you grow sweet peas in instead? They’re actually pretty tolerant with various soils so long as they aren’t too acidic, too alkaline, too nutrient-dense, or hold water for too long in a soppy puddle.
This makes them sound really picky, but there are several soil mixtures that they like. Sweet peas prefer soil mixes that are,
- At the same time moisture-retentive
- And deep
In your soil mix, if you’re worried that it currently holds water to the point it becomes boggy, then adding compost will typically improve its drainage. If your soil is already pretty nutrient-rich, then instead of compost, mix in twigs or sand, or put small, rough rocks at the bottom of the container (if you use a container).
You can tell your soil mixture is nutrient-poor if plants in the soil are turning yellow or it’s too light in color. If you’re not sure, your local garden center should have an expert available to look at your soil sample. Be sure to tell them what you’re trying to grow.
If your soil is nutrient-poor, opt for mixing in some compost, which is loaded with organic material your plants use as food. If possible, find some potassium-rich, peat-free fertilizer instead of nitrogen-rich. Tomato fertilizer, for example.
And what if your soil drains too well? Gardening experts have suggested that using loamy soil with high levels of organic material will sufficiently retain water without turning it into a swamp.
What Soil do Sweet Peas Grow Faster in?
The soil mix we described above will definitely do the trick to make your sweet peas thrive, but you can get your peas to establish themselves and grow faster if you maintain several things:
- High organic content
- A moderate fertility level
- Consistent moisture
- A slightly alkaline level
What would be considered “moderate fertility?” A liberal sprinkling of any fertilizer that is higher in phosphorus than in other components, such as a 10-20-10 Nitrogen-Phosphorus-Potassium (NPK) fertilizer, will be perfect!
How do you maintain consistent moisture? Installing a drip system that is set to supply water on a regular timer is a good way to supply consistent moisture. It’s also possible to set a timer for yourself each morning to soak the sweet pea soil for the day or every other day depending on your climate. What matters is that the first 6-8 inches are consistently moist.
The reasoning behind these simple steps is pretty straightforward. If you maintain the soil conditions that sweet peas like the best, they’ll grow better and be able to grow consistently as often as they are nourished.
How to Fix Your Sweet Pea Soil After Using Ericaceous Compost
If you already have ericaceous compost in your soil mix, you don’t need to start from scratch to grow your sweet peas. Soil mixing is like cooking; you have to make adjustments.
The first thing you need to do to fix your soil mixture is to get the pH level tested to know how acidic your soil is to start with. You can raise the pH level and make the soil more alkaline by adding dolomitic lime or calcitic lime to it.
Dolomite lime is calcium magnesium carbonate, and calcitic lime is high-calcium Ag. The mixes you find will vary in their mixes, but they should give you the ratio on the bag.
Which exact ingredient you need and how much of each you need will vary, but you’ll need a liberal sprinkling to get the pH back to a neutral 7.0.
I know this is quite a bit of homework, but sweet peas are a high rewarding flower when you take good care of them, and they will bring you much joy in your garden.
- Sweet Pea Corner
- Understanding and Correcting Soil Acidity (noble.org)
- How Garden Lime Can Cause Problems (smilinggardener.com)
- What is Ericaceous Compost (Things you Need to Know) (helpmecompost.com)
- What Kind of Soil is Used for Growing Sweet Peas? (sfgate.com)
- What Soil Do Sweet Peas Grow Faster in? (sfgate.com)
- Sweet Peas: Plant Care & Growing Guide (thespruce.com)
- How To Grow Sweet Peas – BBC Gardeners World Magazine