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  • Writer's pictureDavid Brodsky

My perennials aren't doing well, what should I do?

Updated: Oct 4, 2023

The plants in your garden beds may not be growing for a variety of reasons. This blog post is aimed at providing some common explanations as to why your plants may not be thriving as much as you'd like them to be: Buried objects, chemical damage, inappropriate watering, inappropriate sunlight, wrong cultivar, wrong plant for wrong climate zone, wrong soil structure, low soil fertility, pH, soil compaction. Fungi, bacteria, disease, pests, vicinity to other plants,

It can be difficult determining plant problems based on symptoms that your plants show (much like headaches and random pains can signal any number of disorders in a human being, discolored foliage, wilt, and random spots can be symptoms of any number of issues).

Correcting issues with a plant will take trial and error. However, there are many general rules that exist that will help you determine what is wrong with your plants.

1) Buried objects. This can be an issue when it comes to existing grass. On occasion, the culprit to unhealthy looking patches of lawn can be chalked up to objects buried underneath grass. Before overseeding a yellowed or patchy area of lawn dig a foot down and see if you can uncover an issue hidden in the soil itself.

2) chemical damage. This is an easy one. If you've recently applied a herbicide or a fertilizer near or on a plant that's looking damaged (which didn't look this way before) you may attribute the damage to the chemical. Fertilizers (like non fully composted cow manure or most inorganic nitrogen rich mixes) can cause temporary discoloration when overapplied. Herbicides (intended for weedy plants) also damage desirable ones in your gardenbeds. Another chemicals that might cause damage to areas of your lawn is rock salt (used frequently during the winter for snow removal). If enough salt leaches into your soil, it'll make it difficult to get most plants to thrive there, including grass. There are plenty of other chemicals that cause different kinds of plant damage.

3) insufficient watering. This applies to new plants, plants in their first year of establishment, and plants during drought periods (July-August). Most plants that die within two weeks of planting do so because homeowners fail to water them adequately. New plants need their top inch of soil to remain moist for the first two weeks after being planted. Soil moisture is easy to check, stick your finger into the soil, if its wet, it doesn't need watering. When it's bone dry, bring our the hose. For the first year (after the first two weeks) after planting, you generally need to water your plants once a week trying to make sure that the first inch of soil around them remains moist. If a plant is established, it generally doesn't require water beyond what Toronto's weather naturally gives it. However, you should try to water your plants once a week during July and August to counteract the hot conditions. Mulch can be useful in this regard, as it absorbs sunlight during warmer weather and reduces the amount of water that evaporates out of the soil.

4) inappropriate sunlight. Different plants thrive in different sunlight conditions. Some need strong sun 8 hours a day to bloom and others don't. Generally, plants need a lot of sunlight to have vibrant flowers. If you find that your plants aren't blooming as much as you'd like them to be, or at all, in shady conditions where they're planted, consider replanting them in a sunnier area. Alternatively, you may find some plants becoming discoloured under intense sunlight. Some plants need more shade in order to maintain healthy looking foliage and flowers.

5) wrong cultivar. If you are wondering why your shrubs and trees aren't growing as large as you thought they would despite having become established and looking healthy, it may be that you've simply purchased the wrong cultivar. Dwarf shrubs will not grow taller than a certain height regardless of the care you put into them.

6) wrong climate. Toronto exists in Canada's hardiness zone #6 (or USDA zone #5). A city's zone # is determined (by USDA standards) by its average minimum temperature in the winter. A perennial plant rated USDA zones 1-5, will survive in Toronto's winter conditions, a plant beyond zone 6 will either die or struggle. The higher the zone, the greater the chance that the plant won't survive the winter. If your plant hasn't survived the winter, Google it, see if you've been sold a plant that isn't hardy to the region.

7) inappropriate soil structure. Just as plants require certain quantities of sunlight to survive, they also need a particular soil type. To simplify, your soil can be sand, silt, or clay. You can test your soil structure by digging down half a foot and grabbing a handful. Sandy soils feel loose and crumbly (like sand). These soils have large particles with large spaces in between, roots have an easy time establishing in sandy soils. However, the wide gaps allows for water to flow through the soil to depths that roots cannot reach. Some plants can survive and thrive in sandy soils, others cannot. By contrast, clay soils are wet and sticky. They tend to clump together like clay. These are made up of much smaller particles that are very tightly packed together. This type of soil structure holds water very easily. However, it doesn't allow for the same drainage that a sandy soil will allow for, and much of the water stays on the top of the soil line. Roots have difficulties reaching water deeper down in clay soils. Some plants do well in clay soils (particularly those that only need a shallow root system). Plants (like trees) that need the drainage, will not survive clay for very long. Silt soils feel rich, sticky, wet, and crumbly. Silt (we might as well call it well draining soil) is a golden middle between the two other types. Its particles hold water well and allow for it to drain deep underground which promotes long healthy root growth. Most plants require a well draining, silt soil. Toronto has a lot of clay soils. One solution is to grow plants in raised beds with silt soil brought in. You can also incorporate topsoil or compost into your existing soil to improve its soil structure to make the top layer more silt like and conducive to root development. However, note that plant roots can get long and fixing your top layer doesn't mean that your plant will be able to access water and minerals deeper down. A shallow root system does not make for a healthy plant.

8) inapparopriate soil fertility. Plants may not reach their potential in the long haul because the soil that they take nutrients from become depleted. A typical fix is the use of fertilizers containing nitrogen (aids in foliage development), phosphorus (aids in root growth), and potassium (promotes flower/fruit development). These fertilizers will have trace amounts of other nutrients and minerals that your plant needs and should provide a quick boost to your garden. However, these nutrients are soon used up by your plants, requiring regular re-application to create similar results as the year before. You may also promote soil fertility by adding compost crawling with microbiological life into your soil. Compost purchased at garden centers has been sanitized and lacks this life, and is therefore useful mostly as a way of improving soil structure (#7). Doing your own composting or having fresh unsanitized compost delivered is a great way to top off your garden soil, and actually improve the soil year over year. A note on soil fertility, not all plants benefit from a fertile soil full of N-P-K. See the requirements of your individual plant to know what level of soil fertility best suits their growth. Soil tests can be obtained from universities, or more basic test kits purchased at garden centers or department stores.

9) inappropriate pH. pH is a measure of acidity or alkalinity in your soil. If your soil doesn't meet pH standards that your plant requires to thrive, chemicals like lime can be added to change your pH but the change is slow to occur (months and after regular applications). pH testers are readily available at department stores (I like the stick where you just put it into the ground and it gives you a pH reading), and are easy to use. If faced with this situation, bring in topsoil that meets your pH requirements and plant into that, add pH adjusting chemicals to your soil, or find new plants suitable to the pH.

10) weeds and plant proximity. Neighbouring plants will draw nutrients and minerals from the soil that your plant may need to thrive. Regularly cutting back and digging out weeds and planting your various plants at least a foot from each other will give them room to do their thing. Mulch is helpful in this regard as it acts as a blanket to stifle new weed growth and seed proliferation.

11) sick plants. On the safe side, if you cannot diagnosea plant disorder, it might be best to remove and destroy the plant (preferably by burning). You should also remove some of the soil that it was buried in. Some plant pathogens are best removed and burned (along with their surrounding soil). There are certain pathogens that cannot be remedied and requires the destruction (preferably by burning) of the offending plant. Failing to do so means that the plant continues to infect other plants in the surrounding area. Avoid watering these plants as water may spread their pathogens all around the garden.

12) issues to consider bacteria, viruses, pests, fungi, etc

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