We continue with the second part of the horticultural trilogy: Soil. Last newsletter we talked about the importance of providing the right amount of water to your plants and working to group plants with similar moisture needs together.
Soil is the foundation from which your plants grow and the properties of the soil can dictate a plants ability to get the nutrients and moisture they need. Just like the discussion on water, it is critical to understand what kind of soil your plant needs. Not every plant likes a soil with lots of compost, moisture and nutrients.
I can’t cover everything in a short column, but a great first place to start is learning how to take soil tests, this is on online class, Soil Testing for the Home Gardener, at Tower Hill Botanic Garden. I am also running a Soil Workshop at Tower Hill on June 12th, where we will talk about many measurements provided in soil tests and how we can address any challenges in the soil.
If you go to a trusted resource like Michael Dirr’s Manual of Woody Plants (6th Edition), it will tell you the cultural needs of just about any plant. The most important factor to know is pH. You need to match your soil to what your plant requires. The reason that Rhododendron, Azalea, Mountain Laurel and Pieris do well here is because they prefer acid soil and that is what our native soils tend to be with a pH of 4 to 6.
pH is simply a measure of the acidity or alkalinity of your soil. The pH impacts a plant’s ability to take up nutrients and the preference is very different for Lilacs and Rhododendrons. Lilacs prefer a neutral to alkaline soil with a measure of 6.5 to 7. Rhododendrons prefer a pH more in the 4.5-5.5 range.
If you have plants that are not performing, it is a good chance that their needs don’t match the pH in the soil. As an example, Lilac in New England often needs to have lime added to its soil to make the pH more alkaline. They may not flower well or can suffer from powdery mildew if the soil is acid. You may find the need to make soil in one bed more alkaline by adding lime and adding sulphur in another to make it more acid.
Along with pH are meaurements for % Organic Material, Macro/Micro nutrients, Cation Exchange, Base Saturations and more.
So, just like with watering from the last newsletter, we need to group plants together based upon their water needs and their soil needs, and when you have plants that are not performing in a bed, it is often because it doesn’t match the soil or watering requirements of its neighboring plants.
The first place to start is to get a soil test or a number of tests for different beds. The test will inform you of the existing conditions in your beds and offer suggestions for improving it based upon the plants you are growing. UMass Soil Lab is the best option and is cheap for the information you get. There is a lot of information to input, but the site explains things well, and the result of making proper improvements is a substantial improvement in the health of your plants.
I do a lot of tests and help people figure out next steps. I am always willing to consult with people on this critical work. It is pretty cool to take a scientific approach to gardening rather than continually banging your head against the wall. There are books written on this topic and I can’t answer all your questions in 500 words, but hopefully I got you to think about soil as a critical part of your plants success. Not all plants need the same soil or even a good soil.
We have discussed water and soil. Light is the next newsletter, and by matching the needs of a plant by all three measures will allow them to thrive. However, I believe the most neglected measure is the most important: Soil.
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