Fertilizers & Soil Amendments

By Dave Zeldon and Ely Schweyer

As plant people, we’ve all experienced that moment when we realize the novelty phase of that plant we brought home from the garden centre has worn off. The plant isn’t standing quite as tall, the flowers aren’t as bold, and the leaves are unravelling smaller or not at all. What is this magic they perform in the greenhouse? Perhaps you’ve provided sufficient lighting and adequate watering; there’s just one thing that is often overlooked because dirt is dirt, isn’t it?

  97% percent of plant tissue is made up of carbon, hydrogen, and oxygen pulled from the air and water, the remaining 3% is comprised of 16 other elements taken up from the soil. The quality of soil then is crucial to your plant’s health. Whether your plants are in pots or in ground, each soil type you could provide your plant offers something unique and may lack in another.

*Clay particles are even smaller than silt particles.

Resist the Urge to Slam Your Plant in Potting Soil

There’s bags and bags of rocks, sand, bark, manure, and moss on the shelves, yet the common buyer seems to always opt for potting mix. It’s fair; organic matter is usually great for plants and simple to use. However, most people don’t realize it’s merely an ingredient.

   Strictly using potting mix is like attempting to make a loaf of bread out of only flour. All those bags of other materials on the shelves are also components for a successful plant diet!

  Potting mix is a great base material, however, alone it presents risks of compacting, becoming waterlogged, can mold easily, and over time will become depleted of nutrients. Consider mixing the following ingredients into your pots, ground and raised beds to meet your plant’s required nutrients, pH level, and volume of moisture.

🖱️Use our Plant Finder to find some details on your plant! We try our best to keep this updated!

👍 Rule of Green Thumb: Plant roots can help you to determine the medium needed – thick, robust roots (i.e., yucca) typically enjoy chunkier materials, and smaller, delicate roots (i.e., begonias) enjoy finer materials.

Mulch and Bark Bites

• Mulch is the organic slow-release fertilizer, as it slowly decomposes, it lowers soil pH. However, may eventually compact soil once fully broken down.
• In the meantime, it creates shelves in the soil that create air pockets and prevent the soil from compacting. Mulch is a great short term medium for arid potted plants.
• If kept too wet, it can harbour fungus gnat larvae.
• Make sure when sourcing your mulch it doesn’t contain any black walnut.

🖱️ See more on mulching here. 

Sphagnum Peat Moss

• Peat moss is used to help retain moisture and lower pH in the soil given it is harvested from bogs.
• Retains nutrients very well.
• It is difficult to rehydrate once it loses moisture.

Coconut Coir

• Coco coir, much like peat moss is used to keep the soil moist and keep pH low, however it lasts longer and is possibly less invasive to harvest.

Sand

• Grains are relatively large and do not bind, allowing for excellent drainage depending on grade.
• Adds weight to top heavy plants.
• Has no ability to store minerals itself, however, pH can vary by its content of shells, minerals like silica, or fine organic matter.

Manure & Compost

• Source these organic by products locally and ensure they’re not too hot. These additions can significantly lower pH.
• Sheep manure is usually near free of weed seeds as sheep digest seeds better than cattle and horses!

Perlite

• Perlite is a volcanic byproduct (so it floats like pumice) that helps drainage in the soil and prevents compaction – vital in the case of starting seeds.
• If a rockier, well-draining medium is required for your plant, consider perlite.
• Perlite can expand holding trace amounts of water.
• Perlite has a neutral, slightly acidic pH.
• Make sure when sourcing perlite, that you are not being sold Styrofoam balls.

Vermiculite

• Vermiculite is a recycled mineral used similarly to perlite, and too has a neutral, slightly acidic pH.
• Expands with water content.
• Can contain amounts of potassium and magnesium (as well as good cation exchange capacity).
• Runs the potential risk of introducing asbestos into your soil.

Calcined Clay Materials

• Clay materials like recycled brick bits, pottery, or lecca are typically used for arid plants as it improves aeration and drainage.
• Can raise pH.
• Can retain some water.
• High cation exchange.
• Can also be used for starting robust cuttings when kept moist.  
• Probably not ideal for inground amendments.

Maintaining Your Plant’s Dietary Needs

Perhaps we’ve crafted the perfect soil type for your plant – your plant thanks you – but over time, we will end up in the same staling predicament. Why? Because with each thorough watering, we leech the soil of the provided nutrients. Best we use the plant-specific required fertilizer for your plant to prevent nutrient loss.

   Organic sources of fertilizer such as bonemeal, composts, and manures, along with the application of lime, will improve the physical condition of the soil in terms of water and element holding ability. Unfortunately, in many cases though, manures and lime alone cannot be depended upon to provide enough available nutrients in soils with low essential element reserves.

   Let’s talk about commercial fertilizers, which can help target your plant’s exact needs much like vitamins and supplements!

The Scoop on Fertilizers

Of the essential 16 elements your plant pulls from the soil, Nitrogen (N), Phosphorus (P), and Potassium (K) are the most critical for good plant growth. You’ll recognize the three numbers appearing on your commercial fertilizer labels known as the fertilizer analysis of the product, representing the percentage of each of the three "macronutrients" in the order of N, P & K.

Nitrogen (N) is necessary for green leafy or vegetative growth which is important in crops like corn, cabbage, and potatoes.

☝️ It is important to remember that you should not use a fertilizer which is high in nitrogen late in the summer on your perennials, as it may cause a boost of growth which will only freeze as the cold weather sets in. Also, too much nitrogen in the analysis could cause too much lush, leafy growth thus inhibiting the desired flowering aspect of a plant species.

Phosphorus (P) promotes the development of flowers, fruit and roots. Crops like tomatoes, cauliflower and garden flowers.

Potassium (K) boosts plant hardiness, stem strength, resistance to disease and drought which is important to all crops, but especially in potatoes, celery and rhubarb.

👍 Rule of Green Thumb: For foliage plants, provide them with shade and lots of nitrogen, and for flowering and fruiting plants, provide them with lots of sun and lots of phosphorus!

Amending Clay

Hello Haldimand and Eastern Norfolk!

   We’re presented with the challenge of compacted, often shallow and waterlogged clay, which proves difficult but not impossible.

   Clay becomes compacted and waterlogged as it is the smallest soil particle – smaller than a grain of sand, and even smaller than silt – with rough edges that allow it to interlock and bind. In this instance, roots cannot penetrate further into the soil, are susceptible to root rot, and air pockets are slim to none.

   This, however, can be fixed with the addition and renewal of the above materials.

  Mindful that you don’t create a watery bowl in the ground (score the edges the area being worked), you can add organic matter (i.e., manure, compost, and potting soil) for nutrients, as well as mulch, sand and perlite for aeration and drainage. Annual soil particle aggregation in clay soils increases air porosity (air pockets) and is accomplished by the incorporation of organic matter that breaks down to form humus.

🖱️ See more here for planting trees in clay. 

We hope this soil and fertilizer guide helps you provide all the vital nutrients to your beloved plants in ground and above ground! For more information - and soil – visit Eising Greenhouse and Garden Centre! 🌱