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Episode 75 – Sun, Part Sun, Shade – Explaining Plant Light Needs

Ground Breaking Banter - Rick

We often say that gardening is both art and science, and that certainly applies when it comes to determining light (sometimes called exposure) both in your actual garden as well as the requirements of a given plant. While there is unfortunately no super accurate way to determine the light in areas of your yard, it is a kind of, “you know it when you feel it” type of situation. For example, if, on a hot, sunny summer day, approximately how many hours is a spot uncomfortably hot? If it’s at least six hours, you’ve got full sun. If it’s somewhere between 4 and 6 hours, or it’s neither very hot nor refreshingly cool at any point, you’ve got part sun. And if it’s fewer than four hours, you’ve got shade.

The light exposure that you’ll see indicated on plant tags and websites correlates the same: full sun is 6+ hours of bright sun each day, part sun is 4-6 hours or filtered sun all day, and shade is fewer than 4 hours. One important thing to know about part sun is that it is essentially interchangeable with part shade – it’s just a matter of word choice, but the light requirements are the same.

Join us at the YouTube link above or on your favorite podcast platform for our whole conversation. Here’s this week’s Lim-A-Rick:

I’m really lacking sunlight

It’s making me quite uptight

I’ll pop some vitamin D

And drink some hot green tea

Maybe I’ll be more polite. 

My houseplants are experiencing depression

It’s causing a slow digression 

And so I have conceded

That therapy is needed

With a sunlamp intervention 

Why: This is a great example of a plant where the light makes a big difference. Now, the amount of light that hydrangeas need is already a topic of much confusion: people assume they are shade plants, but the fact is that nearly all hydrangeas benefit from some good sunshine, and the cooler your climate, the more sun they can take. In very hot climates, your hydrangeas will need shade during the hottest part of the day. But light affects plants in more ways than you might think – and Fairytrail Bride Cacade Hydrangea is the perfect example of that.

Before we get into why that is, let me paint a picture of this beautiful, very unique hydrangea for you. Fairytrail Bride is known as a Cascade Hydrangea. It’s related to big leaf hydrangeas, but instead of growing rounded and shrubby, it naturally grows with an elegant horizontal habit, with branches that cascade downward. It’s not quite a ground cover, but looks beautiful any place where that unusual habit can shine – planted on a wall, at the rounded edge of a bed, next to a tree, etc. It flowers much, much earlier than other hydrangeas and in fact could be considered spring blooming hydrangea. It blooms around mid-late May for us. Another thing that’s unique about is that the flowers are formed at every leaf axil (point where leaves meet the branches), so those elegant cascading branches bear lots of flowers for a truly stunning display. The blooms on Fairytrail Bride hydrangea – known as Runaway Bride in the UK, where it won best in show at the Chelsea Flower Show in 2018 – are lacecaps, but mophead varieties Fairytrail White and Fairytrail Green Cacade Hydrangeas will be available in garden centers in spring 2025. 

So, what’s the catch, you might be wondering, sounds like a great plant! Well, the catch is that that spring bloom time, which is at least a month earlier than other hydrangeas and maybe even longer, depending on where you live and what type of hydrangea, makes those flower buds much more susceptible to damage from spring frosts and freezes. As such, we initially started selling Fairytrail Bride as hardy only to USDA zone 7. While the plant itself could survive in cooler areas, those earlier blooms were much less certain in areas where late spring frosts can follow periods of warm weather that push growth. But then we made a discovery here in our trial gardens: by planting Fairtytrail Bride in part sun, specifically areas where there is morning shade, the flower buds were able to survive those late season frosts. The reason is that when frost hits, it coats the bud with a mantle of frost. In spots where the plant gets bright morning sun, that sunshine hits it and immediately melts the frost, resulting in damage to the delicate floral tissue. In a location with morning shade, however, the frost crystals do not melt rapidly – instead, they thaw gradually due to warming atmospheric temperatures, reducing the potential for damage.

Fairytrail Bride hydrangea was developed by the inimitable Ushio Sakazaki, a name you might not have heard but if you are a Proven Winners fan, you have almost certainly grown his plants. He’s the talent behind Supertunia Vista Bubblegum petunia, as well as some other favorites like Superbells Lemon Slice calibrachoa and Blue My Mind evolvulus.

Fairytrail Bride hydrangeas are hardy from USDA zones 6-9 and, as stated here, should be grown in part shade, especially with that shade in the morning. They have average water needs and aren’t especially finicky about soil, provided it is well-drained. It is best to avoid pruning them except to remove any spent flowers and dead wood in spring. 

If you’d like to add Fairytrail Bride Cascade Hydrangea– or any of the 320+ Proven Winners ColorChoice Shrubs – to your garden or landscape, you’ll find a list of local retailers here

Gardening Mail Bag - Stacey

Great question, Trixie – even though cool season vegetables can easily live in winter, that doesn’t always mean they’ll be actively growing, especially if night time temperatures are cool. Plant metabolism slows dramatically when exposed to temperatures much below 50°F, which means little noticeable growth. And if metabolism is slow, that also means your plants are unlikely to make good use of fertilizer – plus, since nutrition is unlikely the issue for the slow growth, applying fertilizer would likely be a waste anyway. 

That said, when it comes to granular fertilizers like Espoma, a period of weathering – wind, soil acids and microorganisms breaking down the grain – in order for it to become available for the plant to take up and use. As such, for general purpose spring fertilizing, I usually recommend putting that down perhaps 2-3 weeks before growth begins emerging in the garden or landscape. Regular granular fertilizers like the Espoma Tone products (PlantTone, RoseTone, etc.) don’t need heat in order to become available to the plant (though do note that they won’t weather much in very cold conditions), but time-release fertilizers like Osmacote and Proven Winners Continuous Release Fertilizer, do. In fact, the reason that their packaging says things like, “Feeds for three months” is because these fertilizers release their nutrient load based on temperature. They calculate the amount of time they last based on an average summer temperature, but the hotter your summer is, the less long that fertilizing will last. Note that “time release” or “continuous release” fertilizer like I just described is not the same as “slow release” fertilizer, which would be a more apt description for the Espoma Tone fertilizers. 

Whiteflies are definitely tricky pests to deal with, and what makes them even trickier to deal with is the fact that the majority of information you’ll encounter will be about managing them in a greenhouse – it’s not all that common for them to be a pest in the landscape. That said, I have had them be an issue in my landscape on tomato plants that I purchased that year from the garden center; it’s also far more common in mild climates than colder climates to have whiteflies as an outdoor pest. We do have two simple, chemical-free solutions for you to try, though: one, plant more flowers! Yes, that’s right, and the reason why is that beneficial insects like lacewings, parasitic wasps, and certain true bugs and beetles love to eat whitefly eggs and adults. However, it’s usually only the larval, or baby, stage of these insects that eat the pest, and the adult stage relies on flowers to sustain themselves enough to lay more eggs and bring you more hungry larvae. But the adults need fairly tiny flowers to eat, and thrive on those in clusters: yarrow, Queen Anne’s lace, dill, and sweet alyssum to name a few – see a longer list of suggestions here  – and providing them, especially around your most whitefly-infested plants, will help take care of the problem in time. Another thing you can do is to go out in the garden early in the morning when the whiteflies are still calm and resting and simply cut off and discard the leaves they are resting on. They’re less likely to fly up at this time of day and because they tend to congregate in clusters on the undersides of the leaves, you can get rid of quite a few of them at once this way.

“Why aren’t my hellebores flowering?” is a question we’ve heard a lot, and there are a couple of possible explanations. Both Rick and I have found that hellebores are not especially drought tolerant plants. They’ll live in dry conditions, but they will gradually shrink, and they’ll flower little if at all. But looking at your photo, I don’t think that water is likely to be the issue here – I see you have a lungwort (Pulmonaria), and that’s a plant that would probably already be evaporated if this spot was too dry for hellebores to do well. So another possibility to consider here is maturity. The hellebores you buy in garden centers can be either grown from tissue culture or from seed. Tissue culture plants are typically more expensive but will usually flower their first year (depending on what time of year you purchase them) whereas seed-grown hellebores are less expensive but can take three or more years until they are mature enough to flower. Unfortunately, I know of no way to tell which is which – you could always ask your garden center if they know, and even if they don’t, at least the foliage of hellebores is attractive enough to make it worth the real estate until they bloom.

A  shady garden bed along a wooden fence.

Do you have a question for us? We’re happy to help! E-mail us or use the contact tab above. Due to high volume, we may not get to your question, so if you need an answer quickly, please reach out via the Proven Winners website.

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