Sara Swanson

May Gardening Advice 2017

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Now is the time to plant asparagus.

by Jennifer Fairfield

Well, the weather lately has been living up to its reputation in Michigan – unpredictable! We had fabulous, warm, sunny weather for a little bit, sandwiched in between some chilly (ok – cold) wet stuff. It may not seem like it now, but the weather gurus are saying that this May will be warmer and dryer than normal. Don’t get too comfortable with that though – they are also saying that it will be cooler and wetter in June, while July and August are predicted to be pretty close to normal. What does all this mean to us? Well, if things warm up quickly, we may be able to get some of our warm-weather loving plants into our gardens a little earlier than normal. However, if June is cooler and wetter, you can be sure that we will be battling diseases like powdery mildew, early blight, and fusarium wilt. Keep your fungicides handy!

May is prime gardening time. There’s so much to do this month, and the weather can make getting everything done a challenge. Even if you don’t consider yourself a gardener, there’s still a lot to do, regardless of the size of your yard.

Vegetables and Herbs:

  • Don’t be in too much of a hurry to get some things planted in your veggie garden. Wait until the weather has warmed up a little bit before planting tomatoes, peppers, eggplant, cucumbers, squashes, and most herbs. It’s generally best to wait until there is no danger of frost, which is typically around May 15th. We may have seen our last frost for the year already, but it’s impossible to know for sure. There are two things to look for before planting these warm-weather loving plants: nighttime temperatures consistently over 50°, and soil temps over 60°. Putting your veggie seedlings into cold soil will shock them and can stunt their growth, delaying their fruit production. So, rather than risk that, wait until conditions are right. A soil thermometer takes the guesswork out of that timing.
  • It’s not too early (or quite too late yet, either) to plant onions, potatoes, strawberries, asparagus, broccoli, cabbage, and kale. Don’t wait too much longer, though. Once it gets really warm, you run the risk of cool-weather plants like broccoli and cabbage bolting (going to seed, and being inedible). Onions and potatoes need a pretty long growing season, so waiting too long to get those planted could mean that you end up with little or nothing to show for your efforts at the end of the season. Strawberries and asparagus will need all the growing time they can get this year, and into next year before you see anything edible, so getting them going early will help them get established.
  • One really good reason to grow your own potatoes is that commercially grown potatoes tend to be grown using lots of pesticides. The reason for this is that potato beetles are some of the most destructive pests in the world of crops, and they are also very difficult to kill. So, potato growers tend to go after them with large amounts of chemicals. If you’re not interested in consuming lots of pesticide residue with your meals, growing your own, organically, is a relatively easy alternative. If you’ve never grown potatoes, and don’t know where to begin, this great article from Organic Gardening Magazine offers step-by-step information on a number of different options, including several different container growing methods.
  • Seeds to plant now include spinach, lettuce, carrots, radishes, and beets. About mid-month, it’s safe to plant beans of all sorts. Squash, cucumber, dill, and cilantro seeds can be planted directly into your garden mid-month as well.


  • Plant most annuals in the ground about the same time you plant warm-weather vegetables – once nighttime temps are consistently above 50° and soil temperatures reach 60°. There are some annuals, such as nemesia, snapdragons, and osteospermum, that can stand a few frosts, as long as they have been hardened off. Hardening off is the process of getting plants used to the outdoor environment. If plants have been living in heated greenhouses, then you don’t want to take them from that environment and plant them in cold soil, and leave them to the mercy of the chilly nighttime temperatures that we will be getting over the next week or two. If you buy something that’s been living indoors, gradually get it used to the outdoors, starting with a few hours in the mid-day warmth, and gradually increasing the amount of time you leave it out, over the course of about two weeks. If frost threatens after you have planted things outdoors, use row covers to keep them a little warmer.
  • Most perennials can be planted out any time now – as long as they were grown outdoors or have been hardened off.
  • If you have summer-blooming perennials in need of dividing and transplanting, do this task early in the month, so that the plants have time to put down roots in their new homes before they are expected to bloom. Wait to divide and move early blooming perennials until after they have finished blooming.
  • Mulch flower beds after the soil has warmed up. Mulching while the soil is cold will keep the soil cool longer, and slow growth of your flowers. If existing mulch has compacted over the winter, fluff it up with a garden fork. Compacted mulch keeps water from reaching the plant’s roots. Before adding mulch, work a layer of compost into the soil, or add an organic fertilizer to give your plants a nutrient boost.

Trees and shrubs:

  • Prune summer-blooming shrubs now, but wait to prune early bloomers until after blossoms have finished, as you will be cutting off blooms at this point.
  • Tree pruning should only be done now to remove dead or damaged branches. Oaks should only ever be pruned in the dead of winter, to avoid oak wilt disease. If you absolutely must prune an oak at any other time of year, paint the wound immediately with a latex paint to prevent attracting the insects that transmit the disease.
  • Plant trees and shrubs now to give them a chance to get acclimated before summer heat sets in. Like perennial flowers, make sure that any trees you are purchasing were grown outdoors here in Michigan, or have been properly acclimated to our temperatures before planting them in your yard.
  • When planting trees and shrubs, paying close attention to the details of how they are planted can mean the difference between a tree or shrub that lives a long life and one that gives up in its first year or two. Most important is the depth at which you plant. To learn more, check out this piece from MSU Extension. Another key is making sure that your tree is in the right place. Be sure to learn what conditions the tree needs before deciding where to plant it. Also, make sure that, if you are planting a tree that is going to get tall, you aren’t locating it right below power lines. I’ve been watching the power companies cut back trees up and down M-52 over the last week or so, and it makes me sad to see them scalp a tree all down one side, or cut the middle out of a tree, or take the top off, just because it is growing too close to the lines. I understand they have to – none of likes being without power – so please be sure to keep in mind that your tree is going to grow, and make sure you are planting it in an appropriate place.
  • If you have trees or shrubs that aren’t looking as well as they have in the past, consider testing the soil around them to see if they need to fertilizing. MSU Extension also has a great reference for understanding fertilization needs of trees and shrubs.


  • All the rain we’ve had, along with some warm temperatures have made keeping up with the grass a bit difficult. Mowing when the grass is wet is an easy way to make a mess of your lawn, but letting it get too long makes it difficult to cut, and isn’t good for the grass, either. In general, the grass experts recommend keeping your grass mowed to three to four inches high, and cutting off no more than one third of the blade each time you mow, which means that the grass should be no higher than five to six inches tall when mowed. Mowing higher has all kinds of benefits for your lawn, including helping to prevent grub damage, shading out weeds, and retaining moisture during droughts.
  • Do you fertilize your lawn? Do you need to? The answer to the second question is as easy as a soil test. You can do a soil test yourself with an at-home kit, or you can get an even more comprehensive test from MSU Extension, and find out more than you ever thought you wanted to about your soil. Either way, it’s best to do a soil test before applying fertilizer, so that you know the answer to another question: Do you know what and how much to use? One more resource from MSU is this one on lawn fertilizing, and protecting the water supply while you’re at it.


  • Hummingbirds have been seen in Michigan for weeks now, so be sure to get your feeders out and keep them cleaned and filled!
  • Orioles should be arriving any day now as well, if they haven’t already. They will appreciate both nectar and cut oranges, along with grape jelly, and might just stick around and nest in your yard if you keep offering them such goodies.
  • You can keep feeding birds throughout the spring and summer. Doing so doesn’t, in any way, harm them or make them less able to find food on their own. For most birds, what you put out for them is only a fraction of their food supply, as they are mostly eating insects at this time of year. It’s not entirely true, as some birds are strictly seed eaters, but even those don’t totally rely on you for their meals. Offering supplemental food at this time of year can supplement their diets as adult birds are out foraging for meals for the babies back in the nests.
  • Speaking of nests, it’s not too late to put up bird houses, if you haven’t (or don’t have enough). Birds are still looking around to find good places to raise their young, and the house you put out for them may be just what they were waiting for!
  • When Mother Nature lets up on the rain, you will want to clean out and refill birdbaths regularly, especially as it starts to really warm up. A birdbath can provide you with hours of entertainment, while giving your birds a place to get a drink or get cleaned up.

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