Everything you need to grow Hydrangea’s in zone 3, even beautiful blue, purple, and pink ones!
If you’re like us, the hydrangea varieties you find the most beautiful aren’t naturally adapted to Edmonton’s zone 3 winters. But don’t despair, with a small bit extra care some of the beautiful Hydrangea varieties you love can be successfully grown in our cold climates!
With some overwintering help you can typically grow plants adapted to one climate zone warmer. So for Edmontonians that means you shouldn’t be scared off from a few zone 4 plants in your landscape. For us one of the zone 4 must haves is a bright periwinkle blue Hydrangea.
- Varieties
- Care
- Soil Chemistry
Varieties
Thanks to their variety and popularity Hydrangeas can be a confusing group of plants. There are a number of types, varieties, common names, and brand names. However, there there are really only four types:
- Hydrangea macrophylla – Commonly called Big Leaf, French, or Mophead Hydrangeas.
- Large globe shaped flower clusters – the show stopper of Hydrangeas! An excellent choice for cut flowers,
- The Lacecap variety (H. m. normalis) has a ring of large flowers around a frilly centre,
- The Mountain variety (H. m. Serrata) appear similar to a Lacecap but are often hardier.
- Hydrangea paniculata – Called Panicle Hydrangeas, often shortened to just panicle.
- Cone shaped flower bunch on a panicle (branched multi-flower raceme).
- Sometimes called Peegee, though Peegee is actually a tree form variety of H. Paniculata
- Hydrangea arborescens – Called Smooth Hydrangeas
- Rounded half globe flower clusters
- Hydrangea quercifolia – Oak Leaf
- Oak like leaf shape with a flowers styles ranging from panicles to lacecaps. The foliage changes colour from orange, to red, to mahogany in the fall.
- Hydrangea petiolaris – Climbing Hydrangeas
- Flowering climbing vine type hydrangea.
Most zone 3 hardy hydrangea’s are the panicle type and have green to white flowers. We regularly see the Limelight, and Little Lime varieties in yards around Edmonton. If you’re looking for a white zone 3 hardy Hydrangea the Incrediball is the clear winner. This Smooth type has wonderfully thick semi-circle clusters of white flowers. If you prefer red the Firelight and Quick Fire are zone 3 hardy Panicle varieties, with deep red flowers.
Be careful about size before you buy, Hydrangeas range from small to large hedge size bushes, here’s a helpful comparison chart. While white, green, and red are wonderful, if you’re like us, you want the classic look of thick globe shaped clusters in beautiful blue, purple, or pink that only the Big Leaf Hydrangea’s grow!
Thankfully, with just a little extra care the Endless Summer Original and BloomStruck varieties, hardy to zone 4, can survive our zone 3 winters with only a little extra care.
Plant Care
Planting
First, you want to chose the right spot to plant your Hydrangea. The ideal location has morning sun and part sun to shade in the afternoon to protect from the hot sun. Plant in a north or east facing garden, or in the afternoon shade of larger plants in a south or west facing garden. Hydrangeas are sensitive to drought so use mulch or plant a ground cover to help keep the soil evenly moist.
Fertilizing
We recommend using compost as a natural choice to fertilize all of your plants. You can pick up compost for free at the Ambleside and Kennedale Eco Stations in Edmonton! Add a 3-5cm deep layer around but not touching your plants. If you use petrochemical fertilizers, normally an all-purpose, balanced 10-10-10 N-P-K fertilizer to encourage plant health, larger, and more numerous flowers.
Here are some brands to look for: Osmocote Outdoor Smart Release, Jack’s Classic Hydrangea Fertilizer, Down To Earth Acid Mix, Epsoma Holly Tone. Slow release nitrogen granule fertilizers are the least likely to burn your plants, when the manufacturers instructions are followed. If you use a granulated fertilizer make sure you work the granules under the top of the soil or cover them with soil so they release properly. If you planted an Endless Summer hydrangea like we did, check out the next section on soil chemistry to learn about acidifying your soil for blue and purple blossoms. Some of the fertilizers listed above contain sulfur to lower soil pH.
Pruning
Pruning your Hydrangeas encourages growth, controls plant size, and gives you fresh cut flowers. Pruning depends on the type of Hydrangea you have.
- For H. macrophylla (Big Leaf/French) and H. quercifolia (Oak Leaf):
- Prune in late summer or early fall after flowering is finished. Keep the strong wood and cut dead, damaged, or diseased wood to just above the soil line.
- Flower buds form the year before (blooms on “old wood”) so pruning in spring will remove buds and reduce flower production.
- Prune the oldest 10-30% of the oldest stems every one to three years to reinvigorate growth and flower production. The amount you prune depends on how big you want the plant and how large a flower you prefer.
- Deadhead by cutting below the stem just below flower blossom if you prefer a clean look.
- For H. paniculata (Panicle) and H. arborescens (Smooth)
- Prune in late winter (mid march) to early spring.
- Cut to just above ground for larger flowers,
- Cut to 18-24″ above ground to create a sturdy frame for new growth which will reduce flopping caused by heavy flowers.
Over Wintering
To overwinter zone 4 Hydrangeas:
- in late fall mulch right up to the woody stems to help insulate the plant from the coldest temperatures.
- Buy or make a plant cover cage, cover it with two layers of burlap or a frost protective plant cover fabric, leave approximately one foot tails of fabric drape on the ground, and seat the cover over your Hydrangea securing the cage in the soil or mulch.
- Completely cover the plant cover and fabric tails with snow through the winter to help insulate your Hydrangea and hold your cage in place.
- In the spring when the snow has melted remove the cage and pull the mulch at least 4″ back from the plant stems to avoid problems and diseases caused by excess moisture.
It also helps to plant zone 4 plants in spots that are more protected from wind and close to your foundation to benefit from the extra warmth, but that isn’t always possible given a plants other needs, and it shouldn’t be necessary if you adequately protect them. Thats it, four easy steps and you can open your garden to a whole new growing zone of possibilities! Check out the last section on soil chemistry if you planted a colourful Big Leaf variety like Endless Summer.
Soil Chemistry
Not all Hydrangea’s change colour. Only the flowers of colourful H. myacrophylla and H. m. Serrata (Big Leaf) can change, and the colour is determined by soil chemistry.
Blue flowers require two soil conditions- a pH between 5.2 and 5.5, and available aluminum in the soil. To achieve both results Aluminum Sulfate can be used to both acidify soil and provide the necessary aluminum. However excess aluminum is toxic for plants and will inhibit plant growth. Sulfur, Iron Sulfate, Sphagnum Peat Moss (as a soil amendment during planting), and acidic fertilizers will help to acidify soil without adding aluminum. Always follow manufacturers instructions to avoid damaging your plants.
For Purple and blue-ish purple flowers adjust your soils pH between 5.5 and 6.0, the more alkaline (higher Ph) the more your flowers will change to purple and then pink.
For Pink Flowers you want a soil pH range from 6.0-6.2 (more alkaline) and you don’t want to add aluminum to your soil to avoid aluminum toxicity. Garden Lime will help to raise the pH of your soil, which prevents your Hydrangeas from taking up aluminum.
If you want to start your flower garden we can help, take a look at some of our flower garden design ideas. Enjoy your Hydrangeas this summer!