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Smart Garden 2020: What you can do in early May

Photo: Gail Hudson, UMN Extension Communcations
At last! The weather is turning spring-like in much of the state and we can finally be out in our yards and gardens. It's always exciting to see new and old favorite plants coming up and the leaves opening on trees, shrubs and vines.

I was glad to see bright green buds opening on my new Autumn Revolution bittersweet (Celastrus scandens 'Bailum') a self-pollinating cultivar, and tons of flower buds on the edible Regent Sericeberry (Amelanchier alnifolia 'Regent') and on my Red Splendor crabapple (Malus 'Red Splendor').

To-do-list for May

Aside from staring fondly at your spring garden, there are some tasks you can addressing during these early days of May.

Autumn Joy sedum grows right through leaf mulch
Uncover perennials. Push aside the leaves to expose perennials to the sunlight. Keep leaves on the soil surface as a mulch. Mulch holds in soil moisture, moderates soil temperatures reducing stress on roots, and serves as habitat for beneficial insects. If you're a neat-nik or are afraid the plants won't find their way, don't worry. As temperatures warm, the plants will grow through the mulch and cover much of it.

Leaf mulch also breaks down pretty quickly (depending on the type of leaves, oak leaves take longer), and will add much-needed organic matter to your soil. 

Cabbage is a cool season vegetable

Plant cool season crops: kale, lettuces, radish, scallions and onion sets, spinach. It's still too cool for our warm season crops, like tomatoes, peppers, squash, rutabagas, etc.
Red cabbages: an edible border

I like red cabbage as an accent border in my garden - the grey-blue bloom on the leaves is very attractive. I also like to shred red cabbage with carrots, and toss it with a little olive oil and balsamic vinegar sweetened with maple syrup for a quick 'slaw.

For a calendar and planting guides: When to plant outside

Prune hydrangeas right
above buds
Prune hydrangeas. By now, central and southern part of Minnesota is seeing leaf bud break on hydrangeas. Northern gardeners are still watching and waiting (this is according to my mom up near Duluth the buds aren't opening on her hydrangeas quite yet). Regardless, you can prune off those old tan blossoms by cutting just above a pair of buds. Also prune off crossing branches, damaged branches and dead branches.

This is your chance to also shape your shrub. You can prune off bottom branches on panicle hydrangeas to provide space for low-growing shade plants and provide more of a small tree form.

Maintain structure before plants emerge. This is the time to do maintenance on structure around your plants - walls, timbers, trellises, fencing - to prevent damaging plants by trying to sand / stain / paint around their emerging leaves.

Clean off old plant stems from trellises. Sand and stain pergolas, planters, decking, latticework, etc. before the plants get growing. Stain-covered leaves are not very attractive.

Young garlic mustard plant
Remove invasive plants while they are small. Invasive plants (many of them are registered on the MDA Noxious Weed List) Garlic mustard is emerging now as are thistles and buckthorn is leafing out. NOW is the time to remove these before they get larger! Dig out garlic mustard and thistles or treat with a broadleaf herbicide.

Note that you will likely have to re-treat 2-3 times - these are tough buggers! Young buckthorn can easily be pulled, so this is an optimal time. Cut down large buckthorn shrubs and treat the stump with a, herbicide for woody brush (a "brush killer").

For more on identifying and eradicating noxious weeds: MN DNR Invasive Terrestrial Plants
Choose plants for pollinators. As you enjoy your time out of the house and at your local garden center, look for plants that provide food and habitat for our important pollinator friends. Consider converting all or part of your lawn to bee lawn. Flowers for Pollinators

Author: Julie Weisenhorn, Extension Educator, Horticulture

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