Northerners should be ready with a to-do list so that, whenever they get a chance, they can get their gardening work done. Spring is often a pitifully short season: Some years, in some regions, parts of May are hot enough to feel like summer. Perform all necessary gardening tasks before it gets too hot to work outdoors comfortably.
All Regions
No matter where you live, you will probably need to water the garden some in May. To prevent them from wasting energy on producing seed, deadhead your spring bulbs after they are done blooming. Fertilize your plants. Deadhead pansies and primroses after they have finished flowering. Stay ahead of your weeding chores: Once temperatures soar, weeds and/or invasive plants can quickly get ahead of you. Harvest any remaining cool-season vegetables. Plant warm-season vegetables. Prune shrubs that bloom on old wood after they are done flowering. Turn over your compost pile, or, if it has already broken down, use that compost in the garden and start a new pile. Be on high alert for insect pests and diseases. These include, but are not limited to, aphids, asparagus beetles, cabbage worms, cutworms, scale, snails, slugs, leaf spot, mildew, and rust. Spray for ticks.
Mid-Atlantic
Some days will hotter than others, and you will not feel like working in the garden on such days. Take advantage of cooler days and get ahead on your gardening chores. After all, it will be even hotter next month.
Plant asparagus if you do not already have some. Plant members of the nightshade family. Be prepared to protect them in case of a late frost. Finish sowing seed for annuals. Plant summer bulbs such as dahlias. Give hardy mums their first pinching back to help keep them compact for summer and fall.
Midwest
You have a good chance of getting rain every third day in May in the Midwest. That is just about right to keep your plants happy but not so much as to keep you from getting your gardening tasks done. Be sure to work on the good days, though, unless you do not mind being wet while working.
Plant asparagus if you do not already have some.(Late May:) Plant members of the nightshade family.Finish sowing seed for annuals.Give hardy mums their first pinching back to help keep them compact for summer and fall.
Northeast
May is the closest thing to heaven in the Northeast, although September is a close second. You can still get a frost, though, until the end of the month, which is why the traditional time for planting out tender plants is Memorial Day.
Continue harvesting cool-season crops like asparagus, peas, and leafy crops. Keep an eye out for pest such as groundhogs and rabbits so that they do not get to your harvest before you do. Plant asparagus if you do not already have some. (Late May:) Plant members of the nightshade family. Finish sowing seed for annuals.
Pacific Northwest
May is perhaps the sunniest month in the Pacific Northwest. And with an average high of 66 F and an average low of 49 F, the garden is truly a paradise.
Direct sow the seeds of your annuals. Harden off members of the nightshade family. Once nighttime temperatures stay reliably above 50 degrees F, plant them outdoors. Divide any patches of spring bulbs that you feel are starting to peter out. Deadhead them first, but leave the foliage alone until it yellows. Deadhead rose bushes that are either early-bloomers or repeat bloomers.
Pacific Coast
May is sunny and dry in Northern California. The average high is 64 degrees F, the average low 51. In Southern California is predictably warmer, with an average high of 75 degrees F, and an average low of 57 degrees F. In Northern California:
Stay ahead of weeds. Plant warm-season vegetables, including those in the nightshade family. Keep an eye out for diseases (especially fungal diseases) and insect pests on your rose bushes. Ensure that your automatic irrigation system is in order before summer weather kicks in.
In Southern California:
Direct sow the seeds for warm-season vegetables (beans, melons, squash, etc.).Plant members of the nightshade family.Ensure that your automatic irrigation system working properly.Use large labels to mark where your spring bulbs are planted, now that their foliage has died back. You will need to know their location should you decide to divide them in the fall.Plant warm-weather flowers.Trim off any ratty-looking fronds on your palm trees.Fertilize your roses.
Southwest
In the high desert, expect average highs in the mid-70s F and an average low of 41 degrees F. You will likely have about five rainy days. In the low desert, rainfall drops off precipitously as you progress through the month; by month’s end, you will be having hardly any rain. There is also a marked change in temperature from early May to late May. By month’s end, the daily average high is 99 degrees F, and the average low 74 degrees F.
Plant palm trees.Fertilize palm trees.Plant cacti.Ensure that your automatic irrigation system working properly.
Southeast
Early May is a great time to garden in most parts of the Southeast: Temperatures are still moderate. But with late May comes an average high of 83 degrees F and an average low of 65. You will get eight or nine rainy days in May.
Watch for fungal disease with all that rain. (Late May:) Plant members of the nightshade family. Direct sow the seeds for warm-season vegetables (beans, melons, squash, etc.) and gourds. Ensure that your automatic irrigation system working properly. Plant warm-weather flowers. Fertilize your roses. Use large labels to mark where your spring bulbs are planted, now that their foliage has died back. You will need to know their location should you decide to divide them in the fall.
