May Gardening To-Do List

A spring shrub favorite, lilacs make their appearance this month in several regions. Many communities host lilac festivals to celebrate a local collection of these blooming beauties. If you want to add a lilac to your yard, look for varieties in a size to suit your planting spot. If your yard is already home to a lilac, tackle any necessary pruning right after flowers fade. Plants start forming next year’s flower buds in early summer, so late pruning means you’re reducing next year’s show.

By month’s end, warm-season vegetables should be in the ground in all but the northern-most regions. This includes pepper, tomato, eggplant, squash, corn and cucumbers. Okra, black-eyed peas and melons are also on this list. Plant beans, too, growing several varieties so you have beans for fresh eating and drying. Direct sow seeds into the garden, or tuck in transplants. Once soil is warm, seeds quickly catch up with transplants.

Healthy plant roots are white and fill the soil volume in the pot of a well-established plant. When plant shopping, you can often slip a plant out of its pot by gently squeezing the pot sides to see if the root system is healthy. You don’t need to do it on every plant, but if a plant seems small for the pot or has unhealthy-looking leaves, you might want to check the roots.

Roses have big appetites and need feeding to fuel a stunning flower display. In northerly areas where new growth is just unfurling, top-dress beds with a slow-release fertilizer, scratching it gently into soil, or add a 2- to 3-inch-thick layer of compost. Follow label instructions for whatever plant food you’re using.

In warm-region gardens, plan to feed roses again by month’s end if you’re using a slow-release fertilizer. With liquid rose fertilizer, you’ll need to apply every two weeks until August. Some rose fertilizers include a pesticide to help defeat common rose pests like Japanese beetles. Read the label carefully, because these products often harm beneficial insects and pollinators.

Count on annuals, like these Madness petunias, to add season-long color to planting beds. It takes a lot of energy for annuals to produce non-stop flowers. The secret to success depends on two things: water and fertilizer. Plan to water landscape annuals two to three times a week, depending on rain. Add a layer of mulch to help soil retain moisture. Feed plants using a fertilizer labeled for annuals, following label directions. You may need to apply fertilizer a few times through the summer to keep the flower show going strong.

As you’re choosing plants for containers or new additions to planting beds, select bloomers that nourish pollinators. Butterfly bush gets an undeserved bad rap as “junk food” for pollinators, but the nectar concentrations fall within the parameters of other native plants. The problem is which variety you plant. Do your homework and if you must bring home a butterfly bush, choose one that’s sterile and won’t become invasive, like the original Buddleja davidii. To discover native pollinator-friendly plants, check out The Xerces Society’s list of plants. It’s searchable by state.

One of the best tools you can use in your garden is mulch. It moderates soil temperatures, slows water evaporation from soil and helps suppress weeds. In spring, wait until soil has warmed before adding mulch, or you risk slowing plant growth. This is especially important in northern regions. How thick should mulch be? When using shredded bark, a 2-inch-thick layer will do the trick in most areas. In warmest zones where mulch decomposes quickly, a 3-inch layer is helpful.

If you haven’t done it yet, tune up your lawn mower. Change the oil and spark plug, and add fresh fuel. Remove dried grass on guards or mower decks, and sharpen the mower blade. Consider getting a second mower blade, so you always have a sharp one on hand. Mow your lawn regularly, never removing more than one-third the length of grass blades in one cutting. Cutting it shorter stresses grass and may injure the growing point (crown) of individual grass plants.

A trowel or pair of pruners left lying in a planting bed or on the lawn is easily overlooked. If you tend a plot at a community garden, sharing tools with other gardeners can lead to mix-ups and misplaced items. The easiest way to keep your tools visible is to paint handles a stand-out hue. Choose a color that’s easily spotted, like red, purple, blue or orange. Medium-grit sandpaper gives wood handles a rough edge that helps spray paint stick.

Orioles and hummingbirds arrive in northerly zones this month. Set out feeders with orange slices and grape jelly for orioles. Fill hummingbird feeders with a solution of 1 part sugar to 4 parts water. Orioles also happily sip (or should I say gulp?) this nectar, too, but you’ll need a special feeder to accommodate their beaks. The best way to lure orioles to your feeder is to fill the surrounding yard with orange objects they’ll spot as they fly from treetop to treetop. Lawn chairs, beach balls, kiddie pool — big and orange are the secret to catching this bright bird’s eye.

It’s important to follow weather forecasts in spring to monitor for potential frost. New shoots of peony, hosta and lilies are especially frost tender. Cover them with a sheet, towel, bucket or pot if temperatures are predicted to go below freezing. Remove covers as the air warms the next day. If temperatures dip to 28°F for four hours or more, that’s a hard freeze and most vegetation will burn.

The best way to beat weeds is to start early in the season, using tools that make the task easier. Always aim to pull weeds before they go to seed. That’s Rule No. 1. The second strategy is to use a pre-emergent herbicide like Preen on mulched areas, bed edges and gravel paths. A pre-emergent helps prevent weed seeds from effectively taking root and growing. Follow label directions carefully, and reapply as needed in three months or so. Never apply pre-emergent herbicides to areas where you plan to sow seeds.

Celebrate Mother’s Day with the gift of a beautiful plant, whether it’s a traditional hanging basket for the porch or a tropical beauty, like mandevilla. This year, look for mandevilla with a twist: plants with an attached sachet that will release beneficial predatory mites to feast on spider mites, a common pest on mandevillas. These plants with a built-in pest defense carry the Monrovia label.

Late spring signals the time for fertilizing warm-season turf grasses. Give Zoysia and warm-season Bermuda high-nitrogen fertilizers. Centipede grass needs very little fertilizer and nitrogen. Feed a cool-season lawn as it emerges from dormancy. May is when weeds start to make an appearance in cool-season turf. Spot treat if the problem is small, or for a widespread issue, use a spreader to apply granulated weed killer.

Bunnies are cute, but they’re also challenging pests for any type of garden — vegetable, ornamental or container. Spray repellents applied regularly can help deter these hopping herbivores. Some gardeners swear by Bobbex, Plantskydd or Deer Defeat. Simple physical barriers over or around plants, such as bird netting or chicken wire, also beat the bunnies. Let clover grow in your lawn in spots, and you may find that rabbits head that way to feast instead of into your garden.

Take advantage of brighter sun and longer days to give orchids a fresh start. Whether or not orchids need a larger pot, replacing the growing medium will encourage healthy growth. Remember to use pots that have holes or slits in the sides to let roots breathe. Blend orchid bark mix with very small amounts of moistened sphagnum moss to create an ideal root environment. Always wear gloves when working with sphagnum moss.

Outdoor pests are no joke, whether you’re talking about ticks, mosquitoes, fleas or stinging insects — yellow jackets, we’re looking at you. Homemade insect spray is easy to create from plants you may already be growing. With most DIY insect repellents, you can craft the blend to repel specific pests. Or try fragrant herb bundles like these, which help keep mosquitoes at bay.

Harvest salad crops frequently, including spinach, leaf lettuce, radish or scallions. With leaf lettuce, pick the outer leaves on individual plants, or harvest heads by either pulling the entire plant (if soil is super loose) or cutting, leaving a 1-inch stem stub behind. The stem stub will resprout and yield another crop, especially if it’s early in the month. This harvest method is called “cut and come again.”

Raid your recycle bin and fill the bottom of large container gardens with plastics. This keeps finished containers lightweight and more easily moved. It also saves on soil, which saves you money. The plastics foster healthy plant roots, creating air pockets that provide needed air to roots and help prevent waterlogged soil. By summer’s end, you’ll find roots have completely enclosed the plastics, which, by the way, you can wash and store for repeated use in years to come. Aim to fill no more than one-fourth to one-third of the total pot volume with plastics.

After all danger of frost has passed and night temperatures are consistently above 60° F, gradually shift houseplants outdoors for the summer. Plants may drop or fold leaves at first as they get used to the Great Outdoors. Once leaves appear normal and any yellowing has faded, start fertilizing with water-soluble plant food, following label instructions.

Spider mites typically appear as late spring temperatures rise and rains disappear. These pests plague landscape plants and container gardens. Spider mites are tiny — smaller than a pinhead. They’re usually easiest to spot when the infestation has blossomed and include webbing that drapes between plant leaves and stems. The earliest signs of an outbreak are upper leaf surfaces that appear speckled. Unless an infestation is intense, a daily shot from a garden hose can dislodge pests. Be sure to direct water to the leaf undersides.

In large, heavy container gardens that are permanently placed, it’s important to replace some of the soil each time you plant. Remove the top 4 to 6 inches of soil (more for deeper containers, less for shallow), and add new in its place. Blend in a handful or three of homemade compost, especially if you’re growing edible crops, like this ‘Bright Lights’ Swiss chard. The best potting soil for containers is a commercial, bagged mix labeled for container use. Leave room for a mulch layer at the top of the pot.

Make room for edible crops in existing planting beds. Tuscan kale provides a sculptural backdrop for Echibeckia or other bloomers. Tomato, pepper, cabbage, pole beans — really any vegetable crops can co-exist with annuals and perennials. Get creative with combinations that please both the eyes and the palate.

Dill, fennel and Queen Anne’s lace form flowers known as umbels — wide, flat blooms composed of many tiny blossoms. They’re a favorite among pollinators, including tiny flower flies and more formidable wasps. Don’t plant dill and fennel in the same place, or you risk cross-pollination, which yields future plants that aren’t tasty. Also, be careful of letting any of these drop mature seed into the garden, or you risk being overrun, especially with perennial fennel.

Hydrangeas turn containers into flower fests where the show doesn’t end — even faded blooms look great. Tucking shrubs like hydrangeas into a pot lets you buy smaller, inexpensive plants that you grow to a larger size through the growing season. Six weeks before the first fall frost, transplant hydrangeas into their forever home in the landscape. It’s a great way to stretch your planting budget. This hydrangea, Endless Summer, grows 3 to 5 feet tall and wide and is hardy in Zones 4-9.

Newly planted xeriscape or drought-tolerant landscapes need irrigation to establish. That’s the secret to a successful long-term, low water-use planting. Water plants frequently and deeply the first year after planting. This Colorado garden features tough but beautiful drought-tolerant perennials, including yarrow, Agastache and sage.

A similar irrigation rule applies to newly planted rain gardens. For these landscapes designed to withstand alternating wet and dry conditions, it’s important to water for two years after planting. This ensures that plants develop healthy, extensive root systems prepared to withstand brief periods of saturation and long seasons of drought.

If you have a shady spot that could use some season-long color, look no further than native variegated solomon’s seal (Polygonatum odoratum var. pluriflorum ‘Variegatum’). It thrives in moist or dry shade and offers white spring blooms that beckon pollinators. Variegated leaves look terrific from spring to fall, when they shift to gold tones. The best part comes after frost, when leaves and stems fade and then literally disappear over winter. It’s no-fuss, no-muss perennial perfect for a low-maintenance shade garden.

Spring is a great time to divide perennials that flower in late summer and fall. To determine if a perennial needs to be divided, ask these questions: Has flowering dwindled over the last season(s)? Does the clump have a dead spot in the middle surrounded by a ring of new growth? Are clumps so big they’re crowding paths or other plants? Answering “yes” to these questions means your plant is a candidate for division. Remember to water newly planted divisions. Share extras with friends or a community garden.

Look to desert landscapes to discover the best container materials for outdoor plantings that can stand up to summer heat. Glazed ceramic is a go-to choice over unglazed terra-cotta for two reasons. First, glazed pots come in a wonderful array of colors, including bright blue, red or gold. Second, the glaze coating helps pots retain water better than unglazed ones, which allow moisture to evaporate through pot sides.

Another must-have herb for the garden is basil — and at this point soil and air are warm enough to plant this tropical herb in all but the most northern regions. Gardener cooks prize basil for its flavorful leaves, but pollinators love the blooms. Plant several varieties to learn the flavors, and be sure to include tall, extra-flowering ‘African Blue’ basil (shown). It’s a butterfly and hummingbird magnet.

With perennial garden mums, the secret to a strong fall flower show starts now, when shoots are 4 to 6 inches long. That’s when you start pinching to promote branching, which means more flowers. Simply pinch or snip the last inch of stems until early July. July 4 is an easy-to-remember date for ending the pinch. Say to yourself, “Fall flower fireworks are next” as your signal to stop the pinching process.

Watch for new fire ant mounds in lawns and gardens. The aggressive, stinging critters spread from old mounds during the wet spring and can quickly take over a landscape. Treat new mounds with granular or liquid insecticides soon while they are still small. If you’re unsure what to use, check with your local extension office for the best recommendations for your region.

To savor a midsummer crop of tart berries, prune 1-year-old everbearing raspberry canes, removing just the top one-third of growth. This results in a heavy harvest of exceptionally large berries before the main harvest from this year’s canes ripens in late summer. Thin new raspberry canes, removing any that are thinner than a pencil, spindly or growing outside the perimeter of your patch. A simple tug usually is enough to remove stems.

Late May is the right time to feed citrus trees. Use a specialized citrus fertilizer that contains micronutrients, such as zinc, iron and manganese. If you opt for an organic fertilizer, read the label carefully to ensure it has the necessary micronutrients. If it doesn’t, use seaweed fertilizer to make up for the lack. The exception to feeding now applies to newly planted citrus, which shouldn’t be fertilized for the first year.

When planting tomatoes, don’t worry if seedlings have developed lean or are too tall and leggy. Tomato stems generate roots with ease. A buried tomato stem produces roots — the start of an extensive root system that’s definitely capable of supporting a tomato plant full of fruit. Dig a deep hole or trench, if the stem has a bend in it, bury the stem right up to the lowest set of leaves. Don’t forget to add tomato fertilizer to the bottom of your planting hole.

Plant breeders have been working with clematis for years, developing new flower forms and colors. Bush clematis are worth looking at for a flower border or oversized pot that anchors a planting area. This variety is sold under the name Stand By Me and features dangling, bell-shape blooms in bright blue. Flowers fade to form feathery seedheads that beckon finches to feast on seeds. Plants grow 3 feet tall and wide. They die to the ground in winter, resprouting in spring. Cut old vines back to 6 inches tall in fall or spring to make way for new growth.

If garden space is tight, consider using containers or grow bags to add extra growing area. Smart Pot is the original grow bag brand. It’s made from polypropylene material that lasts for many seasons. When using grow bags, add compost to whatever soil mix you’re using to help nourish plants and retain moisture. Place a layer of 1-inch diameter dead sticks to the bottom of each bag. As the sticks decompose, they’ll help absorb and hold moisture.

To keep sunflowers, gladiolus and other short-lived bloomers flowering all summer, plant some seeds or bulbs every 10 to 14 days until midsummer. This will keep your garden filled with color and give you plenty of stems for picking and bringing indoors. Compact sunflowers like ‘Elegance’ (shown) grow only 20 to 30 inches high but pack real flower power thanks to heavily branched stems loaded with blooms.

Get a jump on floppy plants by inserting stakes in spring as soon as new growth appears. Grow-through type stakes are especially important to add early for plants like hollyhock, peony, monkshood and delphinium. You can also support individual hollyhock stems with bamboo stakes, especially if they’re in a windy spot. Remember that hollyhocks are occasionally short-lived perennials but mostly biennials, meaning one year they produce a tuft of leaves, followed by a flower stem the second year.

Run your irrigation system and observe where the water is going. Make sure you’re watering planting beds and lawn, not pavement. Redirect sprinkler heads as needed, and replace any damaged or malfunctioning heads. Consider adding a weather-based irrigation controller to your system that operates based on factors like rainfall, temperature and humidity. It’s the best way to maximize watering efforts while using the least amount of water. Many municipalities offer rebates when you install irrigation controllers.

Many spring flowers are self-sowing. That means if you let them make seed, you’ll get a head-start on next year’s spring show. Lupines (shown), bachelor’s buttons, dame’s rocket, larkspur, poppies and dianthus are all spring-flowering beauties that happily self-sow and return to your garden year after year. Help the process along by spreading seed, or simply let nature take its course.

May is a great month to tackle path maintenance, weeding and refreshing materials as needed. Pea gravel paths do best when contained within formal edging. Use a pre-emergent herbicide to help keep seed-grown weeds from gaining a foothold. Many gardeners rely on herbicide spot sprays or blow torches to keep weeds at bay in pebble or gravel areas.