There is no place more joyous than a garden center in May. The shelves are full of annuals, vegetables, and perennials ready to go home with you. Gardeners everywhere are waiting with bated breath, trying to find the perfect day to get plants in the ground. Pops of color are emerging as tulips, irises, peonies, and lilacs fill yards.
What you do this month will determine how successful your summer garden is, so strap into your overalls, grab your sunhat and spade, and get outside. Let's install a summer garden. I'll go over the maintenance tasks you should tackle first, then get into the details on what you should plant and how to do it.
Perform a few garden maintenance tasks first
Your watering systems may have taken a hit during winter, so it's vital to check each line before you turn on irrigation for the summer. Often, I've found that I am the problem, having nicked lines while weeding or digging around in spring.
Ensure that the controller is working by standing outside, testing each zone and walking around to check each end point. You can usually hear a leak, so keep an ear out for loud gushing or hissing while also scanning visually.
If you use a hose bib setup, check that as well. We've had a hot spell early on the west coast, meaning my irrigation went on earlier than ever this year. (For plants growing in full sun, water in the morning and aim for 1 to 2 inches of water per week.)
Your established beds can benefit from a layer of compost, which will act as a general fertilizer, as well as create volume back in your beds if they’ve experienced erosion during the winter. Follow the compost with a layer of mulch. Spending this time spreading the compost and mulch will give you the opportunity to size up each part of your garden, so take notes as you go for which areas need weeding, are experiencing pests, or have plants that look like they might not have survived the winter.
Shrubs, trees, and vines
A number of shrubs go through blooming cycles in spring, like lilac and forsythia. Once they’ve bloomed, you can prune them back, and in some cases, like lilac, this may trigger a second bloom later in the season. In either case, it will take one fall task off your list and keep the garden looking tidier.
Lilac in bloom.
Credit: Amanda Blum
This is a good time to plant new woody shrubs and trees—the weather is mild and the ground should be soft from the rains. For your existing trees, make sure you feed them with a fertilizer that is appropriate for them this month. Your garden center can help identify which fertilizer is best for the trees you have. Each of these trees will be creating shoots this month, and you should prune them back as necessary to maintain the shape of the tree and to keep fruit to an amount the tree can reasonably support.
Ensure you are only using clean pruners or loppers—carry diluted bleach or Lysol with you in a spray bottle while outside. Cleaning your tools in between plants ensures that you do not transmit virus, fungus or disease between plants.
Clematis plant climbing the wall.
Credit: Amanda Blum
Finally, climbing perennial vines like clematis, roses, and honeysuckle should be coming out of their slumber at this point, and you’ll want to ensure you’re supporting them by tying them loosely to their trellises as they climb.
Annual flowers
Annuals at the nursery.
Credit: Amanda Blum
It is finally time to put some annuals in the ground, which provide pops of color and can last all summer if you treat them right.
Garden centers should be full of annuals at this point of the year, including petunias, lobelia, marigolds, and begonias. Annuals are a bit more tender than perennials, so you want to wait until you are past the risk of freezing to plant. Annuals can fill an area with color in the space and time between perennials blooming, and are ideal for window boxes and planters, where it might be hard for annuals to survive the winter.
Most hanging baskets have annuals for the same reason—they’re too exposed for perennials or anything else to survive winter. Make sure that the beds you're planting into have a slow release fertilizer like Osmacote in them, and that they will get regularly watered.
Perennial flowers
Most people will have tulips in bloom or just completed at this point—remember not to cut them down after bloom. Tulips need their leaves in order to come back next year, so let them compost in place. Once the foliage has yellowed, it’s OK to divide or move the bulbs. Once the tulip has bloomed, it’s a great time for a bulb fertilizer, so they’ll be strong next year. You can also plant summer bulbs like dahlias and cannas now, if the risk of frost is gone.
You can divide irises now.
Credit: Amanda Blum
If you didn’t get new perennials planted in April, you can still do so now, or divide the perennials you have. The ground should be very workable now, and you may be noticing which plants are ready to be divided as you move about the garden. If you’d like them to bloom this summer, you’ll want to get this task done in May. As you plant, ensure you’re using slow release fertilizer in the ground where you plant.
This time of year, be vigilant in checking your garden center, grocer, and anywhere else that has a "sad plant shelf" (SPS). Stores will discount these plants that don't look especially happy at 50% off or more, and because they're perennials, that's a deal. Plant them as you would any other, and while they might not come back this year, they will next year. Delphiniums and agastache are my favorite SPS finds.
Your roses need a spring fertilizer and might need some shaping at this point or help attaching to the trellis. Look for signs of stress or pests and ensure you’re treating them with appropriate treatments. Your garden center can help.
Vegetables
Onto the main event! Gardeners across the country wait for the precise moment to put their tomatoes, peppers, and eggplants into the ground, and sometime this month, that day will arrive. Here on the west coast, it's usually Mother's Day, but what you're actually waiting for is steady overnight temps over 50 degrees.
If in doubt, join a local gardening group, because this will be the main topic of conversation this time of year. That means it's time to begin hardening off vegetables like tomatoes, peppers, and eggplants as appropriate.
Perennial vegetables like asparagus and artichokes should be active now. Remember to harvest asparagus daily, taking only spears that are larger than your pinky. Once spears become thinner, it’s time to leave the plant alone for next year. Watch your artichoke plants for ants or aphid infestations, which may be sprayed off, but will return without further treatment like neem oil or nearby trap flowers like nasturtiums. Both asparagus beds and artichokes will benefit from a spring fertilizer.
Nasturtiums are excellent trap plants.
Credit: Amanda Blum
By mid to late May, almost all regions should be planting their warm weather crops. Tomatoes, eggplants, and peppers, but also beans, corn, cucumbers, and everything else. Your beans and corn can be direct seeded, as can melon, pumpkin, and both winter and summer squash, but using starts will give you a leg up for the summer.
If you planted potatoes in the spring, it’s likely time to hill up earth around the sprouts.
Strawberry plants that need to be thinned.
Credit: Amanda Blum
Thin out your strawberry beds of runners and give your strawberry beds a dusting of fertilizer. Strawberry plants can either focus their energy on producing these runners or on fruit, but aren’t very good at doing both. Each spring the beds must be thinned to create better and larger fruit. You can give away the runners or plant them elsewhere.
Pest control
Reduce snail and slug populations by putting out traps and going on regular evening hunts. Doing this now, as the rains cease, will greatly reduce problems later this summer. Hang pheromone traps in your fruit trees now, which will control pests this summer and protect your fruit.
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