May Calendar

A few general notes are in order before we get to the calendar. April was so confusing; the unseasonable warm spells followed by harsh cold snaps have thrown the plant community off kilter. You have only to visit your hydrangeas to see the muddle: new leaves, blasted and blackened buds, dead stalks.

Your borders will be showing all its losses and gains by now, and so the spring rush of transplanting will soon be underway.  Remember not only to water well when transplanting, but also to provide sufficient moisture for the roots during their first year in a new location.  Don’t let more than one dry week go by without watering. 

Cornus Kousa, the Asian Dogwood

Before you start digging in and become consumed in the rush, take a few hours (or days) off and look around. The flowering dogwood (Cornus florida) may be seen everywhere this month.  Its cousin, the Asian dogwood, (C. kousa) will be less evident in our local gardens.  Blooming a month later than its ubiquitous cousin, the creamy white or pink blossoms growing on horizontal branches are a stately addition to the garden.  It is unsurpassed as a lawn tree, so keep your eyes open for one. 

When the lilacs bloom you know it is safe to plant dahlia tubers outdoors. Plant your supporting stakes at the same times, at a depth of two inches, as the dahlia heads will need all the support they can get.  When the stems are a foot tall, tie them to the stakes.  Your dahlias will grow anywhere from 18 inches to four feet, depending on your selection. 

This is a good time to visit your local nursery’s collection of tropical and semi-tropical plants.  Bougainvillea or Mandevillea will be wonderfully showy on a terrace or a porch.  They can always be taken indoors to winter over, if you have the patience.      

House Plants Ready for their Summer Vacation

You can start to move your indoor plants outside for their annual summer vacation, but only if you are prepared to whisk them back indoors should the temperature drop precipitously.  I usually wait until Memorial Day as the safest time, unless an early-May visitor can be dragooned into carrying the biggest pots.  

Some gardeners move their houseplants to a shaded location for a few weeks, and then to a location that will give them more light. I keep mine in a shaded location during the summer, as the fresh air and rainfall are enough of a vacation.  As your houseplants will most likely be in small pots, you will have to be meticulous about watering and fertilizing, but you will notice fewer pests outdoors than in.  

If you are planning to repot, now is the time to do it.  Move up one pot size, root prune if necessary, and cut back the top growth in proportion to what you have cut from the roots.  Reshape the plant now rather than in the fall.   

This is the time to get ahead of weeds.  If they are just emerging you can rake them up, but if they have grown to six inches you will need a hoe to pry them loose.   Just be sure to get them out before they go to seed or you will never get ahead of them.   I promise that if you are meticulous about weeding and mulching early in the season, you will be rewarded by a relatively easy summer.

Wet the soil well before you pull up weeds as you will have less disturbance than if you worked on bone-dry soil.  This is a good practice before planting too.  Water to a depth of one inch before planting, and water well again after planting.  You don’t want to drown your new plants, but you certainly don’t want them to dry out.

Take a walk in the woods.  Deep in the forest Carolina allspice, or Sweetshrub (Calycanthus florida) will be showing it’s dark brown-red flowers.  This is the month for woodland wildflowers; make notes about what you would like to see in your own shady edges. 

Carolina Allspice

In the garden, as the lilacs and bleeding hearts fade, bearded iris will take center stage.  The first peony will show itself by the end of May: the red “Memorial Day piney.” It will bloom reliably on time, but the bearded iris will continue to hold the stage for two or three weeks until the rest of the peonies come along.  

WEEK ONE

Keep your gift plants indoors until the nights are consistently warm.

Prune forsythia and other spring- flowering shrubs whenever the blooms are finished.

If the soil is not sticky, sow seeds of hardy vegetables and flowers. Make sure night temperatures are steady at or above 55F.

You might be able to keep pansies blooming through early July by picking off the dead blossoms so that seeds will not form.  If they are planted in a shady spot for part of the day, they will bloom even longer.

Lavender If you are growing lavender, prune it back hard to encourage new growth.

Cut back Russian sage, leaving just six to twelve inches of woody growth.  Pinch out the tips of new growth to encourage a bushier form.

If you see ants on peony buds, leave them in peace; they are harmless.

WEEK TWO

Peonies If you want bigger peonies or roses, now is the time to disbud.  You will have fewer flowers, but bigger individual blooms.  Leave the terminal bud, but pinch off the side buds just below it to limit the number of flowers.

Nights are still too cool to move houseplants out of doors, but you may move tropicals outside if night temperatures are steady at or above 55F.

As pansies die out, replace them with edging lobelia or sweet alyssum.

When lilacs bloom you can plant dahlias out of doors.

Weeds will soon start to overtake flowers.  Don’t pull them out of dry soil; water the garden first.

Order summer-blooming bulbs this month.

Spring gardens are peaking now –- public and private.  Visit as many as you can and take notes.

WEEK THREE

All pinching and disbudding of perennials should be completed by now.

Container Plants on a City Terrace You may set out container plants, but if a late frost is predicted be prepared to cover them with a protective cloth.  It’s best to be patient and wait until Memorial Day.

Seeds of perennials and biennials for next year’s bloom may be sown now through August.

It’s time to sow annual seeds directly in the soil.

Put peony rings in place before it is too late. There’s a moment at which you can longer do this without damaging the plant.

Cut the deadwood from climbing roses.

Start planting perennials and herbs.

WEEK FOUR

Start transplanting seedlings. Work on a rainy or shady day if you can.  If not, water frequently and protect them from the sun.

Ring clematis with lime and dig it into the soil.

Mark the locations for next years’ spring flowering bulbs by placing plant markers.  Don’t cut bulb foliage down until it yellows.

Order bulb catalogs, if they have not yet arrived.

The Unrivaled Common Lilac Consider the lilac. Observe as many as you can, then make your choice.  The hybrids are gorgeous, but my favorite remains Syringa vulgaris, the common lilac.

Continue planting perennials and herbs.

Where spring bulbs have left gaps, sow seeds of zinnia, cosmos and cleome.

Water everything well.  If we don’t have a good rain every seven to ten days water planted beds slowly to a depth of at least an inch.

Buy a rain gauge and set it out in the open.  It will save endless discussions.

Move house plants outside to their summer camp – a nice spot in the shade.

Song birds will have returned by now.  Help them build their nests by leaving six- to eight-inch pieces of string on the branches of shrubs or lying on the ground along with dead twig ends and they will be collected quickly.

This is the time to look carefully at the Bearded Iris and identify the ones you would like to order.  Better still, find a friend who is ready to divide.