Understanding Full Sun vs. Partial Sun: Why It Matters When Planting
Planting the right plant in the right place is one of the most important gardening principles. Full sun vs. partial sun might sound like a minor detail, but it can make or break your garden. Light levels influence everything from growth rate to flower colour to fruit size.
This guide will help you understand the differences between full sun, partial sun, partial shade, and full shade—and how to match your plants to the right conditions for the healthiest garden possible.
Click on these links to learn more about each option:
Gauld Nurseries is your go-to destination for high-quality plants. Let us help you lay the groundwork for a beautiful garden!
1. Why Light Levels Matter in Gardening
Light is the primary energy source for plants. Through photosynthesis, plants convert sunlight into sugars that fuel their growth, flower production, and fruit development. The type, intensity, and duration of sunlight a plant receives are just as important as soil quality and watering habits.
When a plant gets the right amount of light:
It grows at a healthy pace.
Leaves are vibrant in colour.
Flowers bloom fully and on schedule.
Fruits and vegetables reach their expected size and flavour.
When a plant gets too little light:
Stems stretch and become “leggy” as they reach for the sun.
Leaves may yellow and drop prematurely.
Flowering and fruiting are reduced or may not occur at all.
When a plant gets too much light:
Leaves can scorch or fade, especially during intense summer afternoons.
Soil can dry out too quickly, stressing the roots.
Growth may slow as the plant diverts energy to repair sun damage.
Why It’s Extra Important in Southern Ontario
In Southern Ontario, the gardening season is shorter than in warmer climates. This means your plants have fewer weeks to reach full maturity, bloom, or produce fruit. If you give a sun-loving plant like a tomato less than six hours of sunlight, it may never ripen its fruit before the first frost.
On the flip side, shade-loving perennials like hostas or ferns can quickly burn in the bright summer sun, especially during July heat waves. These plants thrive in the filtered light found under maple or oak canopies, where they’re protected from midday rays.
Light Also Affects:
Plant Shape & Colour: Sunlight intensity influences leaf size and colour. Shade-grown plants often have larger, darker leaves to capture more light, while sun plants have smaller, thicker leaves to reduce water loss.
Water Needs: Full sun areas tend to be drier, requiring more frequent watering. Shaded areas hold moisture longer, but may be more prone to fungal diseases if airflow is poor.
Pest & Disease Resistance: Healthy plants with proper light are naturally more resilient. Light-starved plants are often stressed, making them more vulnerable to aphids, powdery mildew, and other common garden problems.
Think of sunlight like a plant’s diet. Too little light is like not getting enough calories—growth slows, and health suffers. Too much light is like overexposure to harsh conditions—energy is drained just to survive. The right balance sets the stage for your garden to truly thrive.
2. The Four Light Categories Explained
Garden light categories are based on the number of hours of direct sunlight a location gets each day. Knowing these categories helps you choose plants that will thrive where you put them.
Full Sun
Full sun means a planting area receives six or more hours of direct sunlight daily. These hours don’t have to be consecutive, but the total should be at least six.
Typical locations: Open lawns, south-facing borders, raised vegetable beds.
Best for: Heat-loving plants that need lots of energy for flowers, fruit, or seeds.
Southern Ontario examples:
Vegetables – Tomatoes, peppers, zucchini
Flowers – Sunflowers, echinacea, black-eyed Susans
Herbs – Lavender, basil, thyme
Partial Sun
Partial sun means a spot gets four to six hours of direct sunlight, ideally with some in the afternoon when the sun is strongest.
Typical locations: Garden edges, near buildings that cast shade part of the day.
Best for: Plants that like warmth but can’t handle full-day summer heat.
Southern Ontario examples:
Vegetables – Cucumbers, peas, bush beans
Flowers – Roses, daylilies, geraniums
Herbs – Sage, oregano
Partial Shade
Partial shade also means four to six hours of direct sunlight, but most of that light should come in the cooler morning hours. Afternoon shade protects plants from intense heat.
Typical locations: Under trees, behind fences, shaded by buildings after midday.
Best for: Plants that need protection from strong afternoon sun.
Southern Ontario examples:
Flowers – Astilbe, columbine, foxglove
Foliage – Hostas, heuchera, lungwort
Full Shade
Full shade means an area gets less than four hours of direct sunlight each day. The space may still have dappled or reflected light, but not strong sun.
Typical locations: Under mature trees, north side of buildings, beside tall fences.
Best for: Plants adapted to low-light woodland conditions.
Southern Ontario examples:
Flowers – Bleeding heart, lily of the valley, Jacob’s ladder
Foliage – Ferns, Solomon’s seal, wild ginger
3. What Happens if You Plant in the Wrong Light?
Light is like a plant’s fuel — too much or too little can cause real problems. While plants are resilient to a degree, putting them in the wrong light conditions often leads to poor growth, reduced flowering, and even long-term damage.
Too Much Sun for Shade-Loving Plants
Shade plants evolved to thrive under tree canopies or in sheltered spots where sunlight is filtered. Exposing them to intense midday sun can cause:
Leaf scorch – Brown, crispy edges or bleached spots on leaves.
Rapid wilting – Even well-watered plants may droop under direct heat.
Burned blooms – Flowers fade quickly or drop prematurely.
Example: Hostas planted in full sun in Southern Ontario often develop scorched leaf tips by mid-July, even if watered regularly.
Too Little Sun for Sun-Loving Plants
Full sun plants rely on long hours of bright light for photosynthesis. If they don’t get enough, you may see:
Leggy growth – Stems stretch toward light, becoming thin and weak.
Fewer flowers or fruit – Energy is used for survival, not reproduction.
Pale or yellowing leaves – A sign the plant isn’t producing enough chlorophyll.
Example: Tomato plants grown in partial shade may produce a few small, green fruits that never fully ripen before frost.
Reduced Pest and Disease Resistance
Light-stressed plants are weaker, making them more vulnerable to:
Fungal diseases – Such as powdery mildew in damp, shady areas.
Insect pests – Aphids and spider mites target stressed plants.
Root problems – Overly shaded, damp soil can promote root rot.
Shortened Lifespan and Poor Performance
Even if a plant survives in the wrong light, it’s unlikely to perform at its best:
Flowering perennials may skip blooming years.
Vegetables may produce smaller harvests.
Overall growth may slow, making the plant look sparse or unhealthy.
Bottom line: A plant’s light needs aren’t flexible suggestions — they’re essential requirements. Matching the plant to the right light from the start saves you time, money, and frustration, and gives you a healthier, more vibrant garden.
4. How to Assess Light in Your Yard
How to Assess Light in Your Yard
Knowing whether an area in your yard gets full sun, partial sun, partial shade, or full shade isn’t something you can guess just by looking at it once. The sun’s position changes throughout the day and the year, so the only reliable way to know is to observe and track the light your garden receives.
1. Choose a Sunny Day for Your Observation
Pick a clear day in late spring or early summer to track light. This is when the sun is high and patterns are similar to what plants will experience for most of the growing season.
Avoid tracking on cloudy or rainy days, as this will give inaccurate results.
In Southern Ontario, late May through early July is ideal for your first light check.
2. Check the Area Hourly
Go outside every hour between sunrise and sunset to see if the spot is in direct sunlight.
Direct sunlight means the sun’s rays are hitting the plant or soil directly with no obstruction.
Light filtered through tree leaves counts as dappled sun, not full sun.
Tip: Use a notebook or your phone to mark down which hours have direct sun.
3. Track the Total Hours of Direct Sunlight
Add up all the hours of direct sunlight the area gets during the day.
6+ hours = Full Sun
4–6 hours = Partial Sun or Partial Shade (depending on whether morning or afternoon sun dominates)
<4 hours = Full Shade
Example: If your vegetable bed gets direct sunlight from 9 a.m. to 3 p.m., that’s 6 hours — a full sun location.
4. Note the Timing of the Sunlight
Morning and afternoon sunlight feel different to plants:
Morning sun is cooler and gentler, making it ideal for plants that can’t handle strong heat.
Afternoon sun is more intense, which benefits heat-loving plants but can stress shade lovers.
Example: A bed with 4 hours of morning sun is better for partial shade plants, while 4 hours in the afternoon works well for partial sun plants.
5. Watch for Seasonal Changes
Light patterns shift as the year goes on:
In spring, bare trees let in more light.
In summer, full leaf canopies can turn sunny areas into shaded ones.
In fall, as leaves drop, sunlight returns to spots that were shaded in midsummer.
Tip: Reassess light levels at least twice a season to adjust plant placement if needed.
6. Use Tools for Accuracy
If you want a more precise measurement:
Light Meter Apps: Many free apps use your phone’s camera to estimate light intensity.
Handheld Light Meters: Affordable devices that measure light in lux or foot-candles.
Garden Planners: Some online garden planning tools let you map sun exposure over time.
Bottom line: By spending a single day tracking sunlight, you can make informed planting decisions that will set your garden up for success for years to come.
Why Choose Gauld Nurseries for Sands & Gravel
Choosing plants that match your yard’s light conditions is one of the simplest ways to create a thriving, low-maintenance garden. By understanding the difference between full sun, partial sun, partial shade, and full shade, you’ll set your plants up for stronger growth, better blooms, and fewer problems.
At Gauld Nurseries, we help Southern Ontario gardeners make the right plant choices for their space. Whether you’re planning a sunny vegetable bed, a shaded perennial border, or something in between, our team can guide you to varieties that will flourish in your unique conditions.
Visit us to explore our wide selection of sun-loving and shade-friendly plants, and get expert advice tailored to your garden. Together, we’ll make sure every plant is in the perfect spot to grow its best.
Plant smart. Grow strong. Enjoy more.
Contact us now or stop by the nursery to get your project off to a strong start.
“We recently completed a front yard and back yard refresh with Paula @ Gauld Nurseries & Landscaping.
Have to say the installation crew are simply outstanding. They arrived early morning as expected and proceeded with their work in an organized and earnest fashion. I was kept informed throughout the day of their progress and was kindly prompted to ask questions. They worked together diligently and well, and were conscientious and mindful of our property. Most impressive of all was that they were so quiet we hardly noticed their dutiful presence.
Thanks so much, Paula! Please keep up the excellent work in beautifying our community with glorious landscapes.”
