Soil pH

AlanGardenMaster
Published on December 4th 2019
18
Soil pH has a great impact on what we can and can't grow in our gardens. Getting it right can also give us better yields and better blooms. It's a key factor that is often overlooked and winter is a great time to take a closer look! at our soils.

Is pH sexy?

  • Soil pH may not sound the most exciting thing to a gardener but it’s essential to get it right for most plants to flourish.
  • You’ve probably heard of so-called ‘lime hating plants’ and maybe even know which ones these are. But do you know that there are many plants that grow better when the soil has lots of lime in it and has a high pH? Read on and I'll cite some examples later!
A close up of a red flower with green leaves
Lime hating Camelia
  • Winter is a great time of the year to delve into this more technical side of gardening and to put things right if needed.

What is Soil pH

  • Before we test our soils, we need to understand soil pH. I’m sure that you will know that pH is the symbol used to indicate whether a solution is acidic or alkaline.
  • A neutral pH is index 7 but in practice for gardeners, we tend to regard 6.5 pH as neutral. This is where the majority of plants will be happiest and will be able to access the nutrients they need.
  • If you want to get technical pH is a measure of free hydrogen and hydroxyl ions in a water solution. The pH scale runs from 0 to 14 but in practice, most garden soils will be in the range of 5 to 8.
  • So if your garden soil has a pH of below 6.5 it’s regarded as acid and above 6.5 it’s alkaline.
A green electronic pH tester in soil
An electronic pH tester gives an instant soil pH reading

Why is this important?

  • It's important because nutrients are more readily available to plants at some pH levels than at others.
  • In addition to this, some diseases are more prevalent in soils with an incorrect pH.

Let’s look at so-called lime hating plants.

  • Perhaps they would be better described as “acid-loving” because they grow best when the pH is below neutral.
  • Most of these are in the heather family [Ericaceae]. Think of Erica, Calluna, Rhododendron, azalea, and Pieris. Those are the most frequent ones.
  • Camellias are often lumped with ericaceous lime hating plants but in my experience, they are far more tolerant of soils closer to neutral. Nevertheless, they thrive in acid soils.
  • The same could be said of most Magnolia trees. However, some magnolias such as Magnolia loebneri varieties are actually lime tolerant so that’s why in spring you'll see magnolias so widely planted in Britain.
  • A few edible plants prefer acidic soil. You might not have thought of blueberries and cranberries [Vaccinium]. They need a very low or acid pH. These are in the heather family too.
  • Potatoes prefer soil pH that’s below neutral as do aubergine and sweet potatoes.
  • Raspberries, blackberries, and strawberries prefer slightly acidic soil.
  • You should certainly be aware of your soil pH if you want to grow these types of plants otherwise you may end up wasting a lot of money!

But what of those plants that like soil pH above neutral?

  • Well, there are masses of these and they tend to be taken for granted. There are some magnificent lime-loving plants!
  • Just think of Clematis, hellebores, lilac, Euonymus, honeysuckles, passionflower, and lavender. I don’t have room to list them all here because it's the vast majority of plants we grow!
A close up of a flower
All Daylilies like limey soils
  • As for fruit plants, there are lime lovers too. Fig, grapes, cherries, nectarines, and plums like alkaline soil.
  • All the cabbage family likes alkaline soils.
  • So that’s sprouts, cabbage, swedes, rocket, pak choi, broccoli, cauliflower, and even wallflowers.
A close up of a cabbage and broccoli
Savoy cabbage
  • Maintaining soil pH above neutral is especially important in combating the root disease ‘clubroot’ with the cabbage family of plants.
  • Many of the lime-loving plants will still grow in acid soils but they perform better if the pH is at or above neutral.

Check it out

  • With this in mind and, especially in planning my new garden, I’m checking my soil pH this week.
  • I’m using a readily available soil pH testing kit. It’s is easy to use and gives a result in a few minutes.
  • There's a simple test tube and chemical tester and an electronic but more expensive hand one with a probe.
  • A useful tip I'd like to share is that the pH can vary from place to place in a garden. Take ten samples over the border that you're checking and then mix it well together. Then check a single sample to get an average.

World Soil Day

  • With #worldsoilday on December 5th, there is no better time to take a closer look at soils.
  • We need to understand where and what to plant but may also need to apply lime to get the soil pH right for planting and sowing in the next few weeks.
  • Just how much lime to add to your soil will depend on the results that you get and what plants that you plan to grow.
  • If you want to grow lime hating plants then you should be able to lower the pH a little by adding flowers of sulphur to the soil or by adding some acid organic matter such as leaf mold.

Remember to use the hashtag #soilislife in celebration of #WorldSoilDay!

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