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Portland Nursery

May Gardening Tips


General Tips

Clean out the pond, if you haven't already, and check your pump to make sure it is clean and in good working condition. Place mosquito dunks in your pond to keep mosquitos under control.

If your pond has water lilies that were sunk for winter protection, it is time to raise them back up closer to the surface and feed with water lily fertilizer tabs (available at the Division Street location).

Plant now for those summer parties and gatherings! (And yes, it is about time to start thinking about bringing the hammock out of storage and setting it up in your favorite shady spot!)

Even though it seems we won't be facing a water shortage this summer, wise water use and water conservation is a good idea at any time. It's good for the environment and the local watershed; and it is actually a good practice for the health of your plants, because it translates into a habit of more even watering, which is beneficial for their growth and stamina, not to mention the health of your summer water bills! We are stocked with a variety of soaker hoses and drip irrigation supplies, and ready to help you get started.

Here's a list for ways to more efficiently use water in your garden:

  • Mulch
  • Water deeply and less frequently, instead of often and shallowly.
  • Water early in the day.
  • Wherever you can, use soaker hoses or drip irrigation system.
  • If you use sprinklers, don't set them so high that they give off a mist, which will just uselessly evaporate away.

Rain barrels are very popular this year, so come to the nursery and get yours (or give one as a gift for your water-wise friends and family).


Perennials, Annuals, and Vegetables

Well, it is annual planting season if ever there was one. Impatiens, petunias, salvia, bacopa… this list of available annuals could get quite long. Delay planting only if it is still unusually cold at night. There are only a few types not ready in May so come on down and get those pots and beds filled.

Ever heard of the thriller, filler, and spiller rule? The basic idea is to get a combination of plants with different growth habits to create a lush and full container display. Go to our Thriller-Filler-Spiller Page, where you will find a list of example plants from the three categories and also check out our Container Designs.

When planting your annuals, pay attention to the maximum spread and allow each individual a little room to grow. Adding granular time-release fertilizers after planting can help keep the plants fed for the next several weeks, helping to encourage vigorous growth and abundant flowers.

As for perennials, the season started a while back but continues now. Many heat-loving perennials are not available until May such as Echinacea and other daisy-like plants. Now is a great time to get both spring and summer bloomers to fill in those blank spots; it may be our best selection of the year.

As for your existing perennials, tidy and fertilize if you have not already done so this spring. Most perennials should be growing well now and can use the nutrition. Also, adding a thin layer of compost on top of the soil can improve the soil and temporarily suppress weeds. Get those peonies, dahlias, and other floppy growers caged so that the blooms will stand up well later on. It is best to get the cage set before the plant has grown up to the height of the grid or ring; if the plant is already tall be careful to gently tuck the foliage into it. This is probably the last acceptable time for any dividing before the heat of summer.

Now or in June is the best time for planting heat loving tuberous plants such as begonia and dahlia. For those bulbs that are blooming or just finished, go ahead and feed them if you have not yet done so this season. Do not remove green leaves from bulbs even if they are floppy. They usually only last a while and the plants need to be absorbing as much sunlight as possible.

Pests are definitely rearing their ugly little heads. Aphids are spreading rapidly, and uncontrolled slug populations can get large this time of year. These can be controlled with insecticidal sprays or baits, many of which are safe for people and pets if not misused. With aphids, a quick glance at the new growth or blossoms can give them away. Look for the soft bodies of any color and dandruff-like molted skins on or near the new leaves. If you have seen what looks like saliva on rosemary, lavender, and other plants you are seeing spittlebugs. While unsightly, they are usually fairly harmless.

Examples of Aphid InfestationsAphidsAphids

Sometimes people mistake hail damage on leaves for insect damage. Consider that possibility when you see holes in the leaves. We can help to identify such questions/problems, of course.



May is generally the first month recommended for planting out most warm-season vegetables such as tomatoes and eggplants. Some people start their squashes and melons in May, though June is often a better time. If the nights are still quite chilly (under 50° F) you may want to wait.

For those who have already planted but are worried about chilly nights there are products to help a bit. Red plastic mulch around the plant or plastic tubes to be filled with water are sold here, and they can keep the plant a bit warmer.

If you did not do so already, make sure to add some lime to your soil when you plant your fruiting vegetables (tomatoes, squash, peppers, etc). This is especially important for tomatoes and squashes, as it helps to prevent blossom end rot.

If you started seeds indoors or in a greenhouse, it may be warm enough to acclimate them to outside temperatures and plant them, but watch for chilly nights; they will be susceptible to cold damage.

It is not too late for most greens and cole crops (cabbages, broccoli, and their kin), but the sooner the better. If it gets hot early in the growing season they may bolt, ruining the crop. Please refer to our vegetable planting calendar for further timing details.


Trees, Shrubs and Fruit

May is a great time for planting woody plants. We have an excellent selection for purchases at this time. The soil is warming and drying a bit, and digging shouldn’t be too hard at this point. When preparing the planting site, remember that the soil underneath the root ball should not be loose; it will compact later and the stem will end up buried too far, often killing the plant. This is especially true of balled-and-burlap (B&B) trees that have a clay-based soil in the root ball.

This is also a fine time for feeding your established trees and shrubs if you have not done so recently. Mature trees or large shrubs may not need feeding; judge this on their performance. If they grow and bloom just fine, it probably isn’t necessary.

Roses are just getting ready for their first blooms of the year. Feed them as well (if you have not recently), and watch for pests. Aphids may have set in, and fungal diseases such as black spot may be starting to grow. We have a separate webpage specifically on rose care.

As established hedges start to grow, this may be a good time to trim for size and shape. Lightly feeding them as well can encourage that fresh flush of growth to minimize the time that they look like they were just cut. Of course, this might mean more frequent pruning with fast growers.

Rhododendrons and other spring flowering evergreens can be pruned just after bloom. This may be the only good time of year for mild to moderate pruning of rhodies because pruning late in the year can ruin the flowers for next year.

With most shrubs, the trimming just mentioned is for mild trimming for size and shape. Removal of large branches is often better for the plant if done in winter.


Indoor Plants

Wash the leaves of indoor plants and check/treat for pests and diseases. If you suspect you have a problem with a plant and are not sure what it is, bring a sample to our Info Desk. We carry a full line of safe products for houseplants and tropicals.

It's time to be feeding most indoor plants, as they actively put on growth. We have several types of indoor plant food, and recommend Whitney Farm's Ellie's liquid as a good all-around fertilizer. Give us a call if you have questions on feeding or care of specific indoor plants.

Start setting houseplants outside in a shady location for some fresh air. If you have any questions about particular plants and where they like to spend their spring and summer, feel free to call either of our locations (for houseplant questions, some members of our Division Street Staff are especially knowledgeable; that location has the broader selection of houseplants and tropicals and therefore the opportunity for more personal experience).




Hosta 'Island Charm'
May Perennial Pick - Hostas
Read about Hostas

Helpful Videos

Click photo to play video Videos will load automatically. Visit the GardenTime TV website for more GardenTime videos.

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Jan McNeilan's May Tips

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