So here’s the 5 main things to understand when you buy plants:
1. Hardiness Zone
2. Average Mature Size
3. Sun Exposure
4. Watering Needs
5. Planting Instructions
This can be unnecessarily complex: there are USDA Plant Hardiness Zones which includes Canada, and bases hardiness zones on average minimum winter temperatures; Plant Hardiness Zones of Canada, which also uses average minimum winter temperatures but is different from the USDA zones; and Sunset Zones, which are much more comprehensive, using average warm and cold temperatures, humidity, length of growing season, and other factors, but which unfortunately is seldom used on plant labels or any other resource.
Most plant labels, even plants that are sourced in Canada, will use the USDA zones, so let’s go with those. Here in coastal BC most of us are in Zones 7b (slightly less cold than 7) to 9a. So bottom line here is that plants that are “hardy to zone 10” will generally die in average Metro Vancouver winters, and therefore are what we generally call “annuals”. But “hardy to zone 8” means we’re fine. This is the label to Rhodo ‘Jingle Bells’, Zone 7.
There are a few things you can do with zones, first of all knowing what your own zone is: Here’s a great little site that you can zoom in and find your own almost neighbourhood zone. For example, I live in south Burnaby, zone 8b. Parts of North Burnaby are zone 9a, because it is closer to the protected Indian Arm of Burrard Inlet. Another thing about zones, is that you can “bend the rules”, depending on your own gardens microclimates. If you have a sheltered spot from the wind, you might be able to grow things that are technically rated as needing more winter warmth. There are lots of ways you can push the boundaries; that’s what Google is for. OK, enough already about zones. Let’s move on to…
Average Mature Size.
The above label says the “average size” of R. ‘Jingle Bells’ (implying “mature size”) is 3′ tall and 4′ wide. When you’re planting say two of these, the distance between the trunks of the two should be at least 4′. If you plant it next to something that grows to 6′ wide, you’ll want to have 5′ (radius of one plus the radius of the other) between the two trunks. Knowing its mature height allows you to determine if you can plant something nearby that will look good towering above it, or if it would comfortably shelter something growing underneath it.
Now here’s a classic example of unhelpful;
Here’ s the unhelpful part:
“Slow growing to 6 to 8 ft. tall and wide, larger with age“. So if it doesn’t grow older, it won’t grow bigger. I’ve planted it in front of Rhododendron ‘Johnny Bender’, hoping that JB will grow bigger than the label says (5′ T and W) and that NP will NOT “grow larger with age”.
A quick primer on Sun/Shade Exposure, starting with: spend a few days in various seasons watching where the sun hits the ground in your many garden areas.
Full sun: 6+ hours of direct sun
Part Sun or Part Shade or Dappled Sun or Light Shade: 4-6 hours of direct sun, maybe divided into early morning and later afternoon, or all early morning, or all later afternoon, or right across the hottest part of the day.
Full shade: At the most 1-2 hours of direct sun. But if your full shade has lots of full sun nearby, it’s still pretty light, and might support lots of “light shade” kinds of plants.
Dense Shade: not only no or minimal direct sunlight, but lots of dense things hiding sun: like your own building and a highrise 20 feet away, and a 50′ cedar over to the right, and a maple to the left. That’s DENSE shade.
“South Facing” or “North facing” or whatever doesn’t always mean much. My “North facing” front yard is actually in full sun from 8 am until 8 pm. (in the summer), while my “South facing ” backyard has lots of areas that have no direct sun ever.
Water Needs and Planting Instructions
Almost every plant tag will recommend “fertile” soil. (There are a few plants that actually prefer poor soil, but that’s for another day…). So let’s assume you have decent topsoil and a little organic matter (compost, sesasoil, mushroom manure…) added. Once you have soil that will support decent plant growth, you should place together plants that have similar watering needs. For example, many sedges are the kind of plants that grow along river and lake edges, so should be in really moist soil. Don’t plant them in raised beds that will dry out quickly (unless everything in that bed needs to be in really moist soil). Lady’s mantle (Alchemilla) and salvia are very happy in drought conditions (after giving them a few months to grow deep roots). So plant them together and don’t water them like the sedges.
Good plant tags will include watering instructions, but they don’t take into consideration what else might be going on in your garden–which of course the growers can’t do! Most plants need excellent watering their first year after transplantation (from the grower’s environment to your environment). After that they should only receive the amount of water they would need in their native climate. Many plants won’t need any extra watering above what we get in an average growing season. Best practice: grow plants together that have similar food and water needs.
There’s so much more to say on all these subjects, so if you have questions, do post them and I’ll either give you answers or direct you to answers. As always, look forward to your comments; click on the follow button to get regular posts fro RLGS.
Not sure I follow your logic with regard to hardiness zones. If your area ranges from 7b to 9, then a plant that is “hardy to zone 8” isn’t necessarily “fine” for those living in 7b. It might be OK, but since 7b is colder than 8, it might not.
Now, speaking as somebody who is responsible for what goes on the pot tags at many nurseries, I’d say that the info there may be even less helpful than you think. For one thing, plant description is not an exact science, or at least the science hasn’t been done for most plants. The info on the tags often is derived mainly from nursery websites. Whenever possible, I try to get it from botanic gardens, plant societies, and universities, but nobody can keep up with the enormous number of new introductions that show up every year, so it’s often necessary to look at less reliable sources. So, what’s on a tag may be just the opinion of whoever is offering the plant for sale, and those opinions can vary considerably. If the breeder provides this information, then it’s more consistent, but often the biggest breeders provide the least info, depending instead of flashy photos. After a couple of years at my job, it’s still a mystery to me how plants from these breeders ever get described in a way that means something to home gardeners. Also, it’s questionable whether they subject all their plants to a wide variety of conditions. Maybe that’s why they don’t provide much info.
Heights are often given for 10-year-old plants, but that sometimes isn’t mentioned, so it’s taken as the ultimate height. One reason for the 10-year figure is that nobody wants to wait around for new introductions to grow for 50 years to see how big they get: gotta sell ’em! That’s not entirely unreasonable in some cases, but it ought to be acknowledged.
It’s often the case that if you ask a dozen nurserypeople about a plant, you get a dozen different descriptions and care instructions. Sometimes that’s because experiences differ by climate or whatever, and sometimes it’s because the nurseryperson doesn’t have enough of a clue about what they’re selling even to correctly write its name. Some nurseries, especially smaller ones, are run by knowledgeable plant enthusiasts, but many are just plant factories. Imagine a car dealer who doesn’t know the make of the car he’s trying to sell you, or how to spell it. One sees a lot of that in the nursery business.
I’d suggest using the info on plant tags with a large grain of salt. If you aren’t sure about a plant, do your own research. I like to use independent institutions like the Missouri Botanical Garden (mobot.org), and plant societies, either general ones like the Royal Horticultural Society, or plant-specific ones like the American Rhododendron Society, whenever possible. I generally avoid discussion forums because, in my experience, gardeners are happy to share information, but what they provide is often questionable, based on a tiny sample size, or based on climate or other considerations that most others don’t share. The UBC Botanic Garden does have a pretty good forum, though.
Excellent follow-up to this almost 6 yr-old post! Thanks Knox.