April garden checklist

UNIVERSITY OF MINNESOTA EXTENSION - www.extension.umn.edu

Mystery of the month

How do you identify which animal browsed on your shrubs over the winter?

Find the solution to our mystery at the end of this article.

Pests and diseases

Do not prune oaks from April through October. The fungus that causes oak wilt is most abundant during these months.

Check out our Oak wilt in Minnesota webpage for more information.

Trees and shrubs

Prune spring flowering trees and shrubs, like lilac, azaleas, and forsythia, after they finish blooming.

For older lilacs with lots of large stems, follow the rule of thirds. You can remove a third of the large stems all the way to the ground in the spring of the first year, cut half of the remaining large stems in the spring of the second year, and remove the rest of the large stems in the spring of the third year.

Common lilacs only flower on 3-year-old wood, which is why we use the rule of thirds. This is also a type of rejuvenation pruning. We want to have beautiful blooms every year while we work on rejuvenating our plants.

• Growing lilacs for Minnesota landscapes has more detailed information.
• Watch the shrub pruning video series for how to prune an overgrown lilac.

Flowers and other garden plants

Once your garden beds warm up and plants emerge, push back protective mulch (wood, leaves, straw, etc.) covering perennials. If temperatures are still dropping into the low 20s at night, it’s easy to push the mulch back over any tender perennials.

When temperatures dip to 20°F or lower, some perennials can suffer cold damage. Leave the mulch on the soil around your plants.

With 3 to 4 inches of mulch, you can moderate soil temperatures, reduce weeds, and retain moisture throughout the growing season.

Watch this Hort Short video on pulling mulch away from perennials.

Houseplants

Have the flowers from your potted bulb garden faded? Some forced bulbs transplant more successfully than others in the landscape. For example, forced daffodil bulbs transplanted in the landscape may regrow and bloom in 1 to 2 years if the plants are cared for properly.

When the flowers in your potted bulb garden fade, place the pot in a sunny window until it is warm enough to move it outside (~50°F at night). Then, put the pot in a sunny location and continue watering it. The leaves need to collect the energy from the sun (photosynthesis) and store it in the bulb for future growth and (hopefully) blooms.

When the leaves start to fade in early to midsummer, stop watering. Remove the bulbs from the pot and let them dry out for a few weeks, but don’t let them get so dry that they become wrinkly. Then, store them in a paper bag in a cool location (45-50°F).

In the fall, plant them in your garden with your other spring flowering bulbs. Be sure to label them.

Lawn

Start thinking about weed control for this spring. If you did not dormant seed, are not planning on seeding this spring, or are concerned about crabgrass in your lawn, consider applying a crabgrass preemergent herbicide.

You can use the Turfgrass Dashboard to determine if it is too late to apply a pre-emergent herbicide.

If crabgrass has already germinated in your area, use herbicides containing the active ingredient dithiopyr (which has pre- and early post-emergent activity); otherwise, prodiamine and pendimethalin work best to prevent crabgrass from emerging. 

As always, dense and healthy turf is the best defense against weeds. Proper mowing and fertilization can achieve this.

Check out the Lawn Care Calendar to learn more about proper timing for the best lawn management practices. 

Other tasks

Direct sow cool-season vegetables and flowers in April as soon as the ground is dry enough to be worked. Some plants you can sow include lettuce, radish, peas, flowering sweet peas, and Johnny jump-ups.

You can transplant pansies and other cool-season flowers as soon as they are available at your local garden center. The plants should already be hardened off when you purchase them.

• Starting seeds indoors has a table on starting plants from seed.

• Vegetables A-Z has detailed information on growing various vegetables in Minnesota.

The tree has distinct 45° cuts on the end of the stems and bark that has been gnawed off at the snow line.

Solution to the mystery of the month

If you see 45° cuts on stems, you know you have rabbit damage!

You may also see the bark has been gnawed off, which usually kills the stem, and perhaps some droppings in the area. These are all typical signs of rabbit damage.

You can use clean, sharp pruners or loppers to cut shrubs below the damaged stems.

This fall, protect your trees and shrubs from animal browsing.

CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Be sure that the area you wish to treat is listed on the label of the pesticide you intend to use. Remember, the label is the law.