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Help! The soil I bought is killing my plants!

Updated: Nov 3, 2021

Have you ever bought soil to only discover you can’t grow anything in it? Are your plants looking unhappy? Not to fear, we have some tips to help!

In our last post we talked about how to choose soils that a fit for purpose for vegetables and non-native plants. This post gives you some tips and tricks to consider if you have purchased soil that doesn’t seem to be growing any plants or when your plants don’t look very healthy.

Troubleshooting soil problems can bring back plants (Photo:J Drake)

Help your soil recover

Soil stripped, moved and sitting in a big pile will not have optimal nutrient cycling, soil biology and organic matter. This means that the soil doesn’t have optimal properties for growing plants. The longer the soil has been in a big pile (>2m tall) the longer it will take to recover. I always recommend buying ½ soil and ½ mushroom compost. When using the soil and compost mix, I suggest adding some of your own compost, watering in well and regularly when it is dry, and using a green manure or cover crop, knowing it will take three to six months for the soil to recover and for plants to really thrive again.

What symptoms do you plants have?

Record a diary of your plant symptoms. Do your seedlings just die? Do the leaves curl, go yellow and then brown on the edge? Are your berry leaves red? Have your citrus leaves gone yellow? Can seeds germinate? Your leaves are a good indicator of what is going on in your soil. If your species is responding a certain way to the soil, look it up on a reliable website or book and you may find a solution. For example, yellow citrus leaves are usually a nitrogen deficiency, but may also be the result of high pH (i.e. basic/alkaline soils) or an iron deficiency in soils lower in plant available iron (e.g. potting mix), so you may need to add both to soil. Be careful to only use small amounts of nutrients and see how your plants respond over a few weeks. Adding too many nutrients could cause other problems, such as phosphorous deficiency. Yellow and brown leaves that are curling in vegetable crops can often be a lack of water – check the soil to see if it is dry, try watering more often, adding mulch and making sure your soil is moist. The same symptoms could also be the result of high salt concentrations in your soil. Some plant health symptoms may be the result of more than one problem, and try to rule them all out one at a time.

Check your pH

Use a soil pH test kit to check the pH. Different plants prefer different pHs, but most vegetables do best when the pH is 7. If your soil is acidic (pH <6), try adding some lime to increase the pH. If your soil has a pH >8 try adding some manure or other organic matter to reduce the pH. pH also influences nutrient availability to plants. Altering the pH of your soil may make key nutrients more readily available for plant use.

Check your soil moisture

Stockpiled soil can be hydrophobic -- this is when soil repels water. If your soil is doing this, chances are your plants might not get enough water or nutrients either. Many nutrients are carried to plants in water, and plants showing deficiency for these nutrients – such as potassium – can actually have enough nutrient in the soil if only there was enough water to carry it to them. Adding plenty of organic matter (compost, mulch and manure) helps your soils recover and to hold moisture.

Test your soil

If you have tried the options above and you still aren’t sure what is happening, test your soil! Send it off for a general screen of characteristics that are essential for growing plants. We suggest sending soil to VegeSafe for heavy metals and EAL for other nutrients (EAL RA-PACK-001). You will get a report from them that considers human health (VegeSafe) and plant growth in soils (EAL). We also like to use Interpreting Soil Test Results, a book about understanding soil tests published by CSIRO.

Could my problem be something more sinister? Like chemicals? Jules will be writing a blog post about this issue next.

Troubleshooting problem with your soil is not always a guarantee that you have solved a problem, but should help you to rule out more common issues before being worried about more serious ones.

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