May Gardening Tips

May is one of the most exciting months in a Michigan gardeners world.  You have most likely already started the process of hardening off your seeds and given some thought to what annuals you are going to plant around your yard. This time of the year can also be very deceiving, as warm temperatures suddenly give way to cold, frosty evenings that can turn your lush backyard into crispy slumped-over plants in one night.

Remember that most annuals are frost sensitive. Cover plants with fabric or paper when there is a freeze warning. Most perennials are acclimated enough to resist damage by frost.

In Michigan, the last frost date is right around May 15th-20th. We often can’t wait that long (and why should we) to get going with our annuals and vegetables. Much care should be taken if you plant outside at the end of April and the beginning of May. If temperatures fall below 40 degrees, I wouldn’t take a chance and cover your tender vegetables and annuals and bring in your houseplants (most houseplants should be brought in if temps get below 50 degrees). If you are using a covering, avoid plastic. It is generally thought that because of the makeup of plastic it gets just as cold as the air and can allow freezing it touches the plants. Fabrics are best, followed by newspaper.

This is an example of frost damage on a tomato. Leaves turn brown and curl at the edges. Severe frost will cause the entire plant to wilt.

Here are some reminders on what should be going on around your yard this month!


Sow your last crops of cool weather plants such as lettuce and broccoli early in the month.

Sow the remainder of your seeds outside after the last frost date, or be prepared to cover your seeds with a sheet or newspaper.


Sow and plant so that you will have a rotating crop. This prevents insects and disease from taking hold of your garden.

If you had late blight last year and have not begun treating the area, consider that area of your garden contaminated and do not plant there! Contact Flowerland for further direction and advice.

Plant seed potatoes in an area that has good drainage after last threat of frost.

Remember to share your crop with friends and neighbors. Call your local food bank in advance to see if they accept donations of fresh fruits and vegetables.


After blooming it is tempting to cut down the foliage of tulips and daffodils. Resist this temptation! Bulbs are building up energy for next year before they go dormant, leave this foliage until it has turned mostly yellow, and then cut (do not pull) them off.

After tulips and daffodils are done blooming, you may cut off unsightly dead blooms, but leave foliage as it it gathering energy the bulbs will use to flower next year.

Plant summer bulbs! Plant your elephant ears you have started inside after last threat of frost. Plant glads and dahlias, making sure to mark where bulbs are so you can dig them up in the fall.


After the threat of frost and temperatures below 50 degrees it is safe to move your houseplants outside. Never place your houseplants in the hot direct sun even if they are full light plants. They are delicate and can burn in under an hour. Instead choose an area of your patio or porch that will get dappled sun, or shade. Outside light is intense enough to meet the needs of high light plants even out of direct sunlight.  You may need to increase your watering schedule with the temperatures, and check often for insects and pests.

Trees and Shrubs:

If you are planning on trimming your Rhododendrons and Azaleas, do so immediately after they have bloomed. They will form winter buds, and you will trim off next years buds if you wait too long.

Continue to trim out tent caterpillar nests.

Treat white-barked birches for birch leafminers.

Damage from Birch leafminers. If left untreated they can defoliate a tree in a single season and weaken the trees defenses against weather and disease.

Treat your ash trees. Emerald Ash Borers begin to appear late in the month, without treatment, they will surely overrun your trees!

Watch for spider mite activity on Canadian Alberta Spruce, Boxwood and Burning bushes. They can also be found on other shrubs, but these are some of their favorites.

Catching spider mites early is the key to successful treatment. Watch for brown patches on Alberta spruce and drooping leaves on Burning bushes that have been appropriately watered.

They are many other insect problems that begin this month. If you are having a problem, cut off a good sample showing damage and the insect (if you can’t get both choose the insect), place it in a zip lock bag and bring it in to us. We can ID your problem on site and then give you options for solutions.  If you have a digital camera snap some overall shots of your problem and bring your camera in with the sample.

Plant trees that have color this month including Kousa Dogwood, Redbuds and Flowering Crabs! It is also time to plant fruit trees. Many fruity trees require two different varieties to pollinate properly-consult a nursery specialist to help you choose your fruit tree varieties.


When planting annuals first loosen the plant from the pack by squeezing the bottom of the cell pack. Turn the cell on its side and as you squeeze up on the bottom grab the entire plant at the base and pull it out.

Loosen the bottom part of the roots to help establish you plants.

It is always a good idea to loosen the the roots of plants you have just bought. This includes everything from trees to little annuals. This helps the plants development and root establishment.

Always be sure to water after you have planted, and keep unplanted flats moist as well. Don’t store your flats in the full sun, instead keep them in the shade until you are ready to plant them.

Lawn and Weeds:

Apply pre-emergents such as preen to keep control of weeds in your garden.

Pull perennial weeds such as dandelions out of your garden.  Be sure to get the whole root, as they can regenerate easily. If your job is too big,  Scotts Weed and Feed can work wonders on your lawn!

Don’t apply weed killers to newly seeded lawns or allow children or animals to play on applied areas.

Now’s a great time to lay down sod. Watering is the key to keeping your sod alive! Never let your sod dry out. Use a box-cutter to cut your sod to shape when laying it down. See Flowerlands online care sheets for more information!

Laying sod is easy and rewarding! Keeping your sod well-watered will keep it healthy and green.

Apply step two of your four-step program. Apply when the grass is moist and do not water for 48 hours.

Other information:

Garlic mustard is starting to bolt-pull before its too late! Early in the month Garlic mustard is in flower. Get out with your garbage bags and pull! Each plant left flowering can produce up to 8,000 seeds that are taking over our fields and forests (Remember not to compost, or leave plants on the ground-they can still seed!).

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