Yes, you can plant perennials in summer, but you need to work harder to keep them alive through the heat. Your success depends on picking the right plants and giving them extra care during those first weeks in the ground. Summer puts stress on new plants that spring and fall don't create, so you have to plan around it.
I learned this lesson in my shade garden during a July heatwave. I tried adding a dozen hostas, and half of them turned crispy within two weeks. My daily watering wasn't enough to save them. The next summer, I planted coneflowers and sedum instead. Every one of those tough plants made it through fine.
Heat above 90°F (32°C) creates serious problems for your newly planted perennials. The roots sit in hot, dry soil where they struggle to grow outward into your garden. At the same time, the leaves lose moisture faster than those tiny roots can replace it. This imbalance causes transplant shock that can kill your plants within days if you don't step in to help them along.
Summer perennial planting works best when you choose tough plants bred to handle harsh conditions. Coneflowers laugh at summer heat once their roots grab hold of your soil. Sedum stores water in its thick leaves and barely notices dry spells in your garden beds. Daylilies and Russian sage both thrive in full sun and tolerate the worst summer throws at them. Start with these forgiving plants before you move on to fussier ones.
Timing matters more in summer than any other season for your new plants. You should plant in the evening hours after 6 PM when the soil has started to cool down from the day's heat. This gives your plant's roots all night to settle in before facing another hot day. Morning plantings force roots to endure eight or more hours of heat before getting any relief at all from the sun.
These hot weather planting tips made the biggest difference in my summer survival rates over the years. Water your planting hole until it pools, then let it drain fully before setting in your plant. Water again after you backfill the soil around the roots. Spread 3 inches (7.5 cm) of mulch around the base but keep it a few inches away from the stem to prevent rot problems.
This mulch layer cuts your soil temperature by up to 10°F and holds moisture right where roots need it most during the hottest parts of each day. You can also give stressed plants shade during their first week to help them adjust to their new home. I prop up an old patio umbrella or lean a board against stakes on the sunny side of new plants in my garden.
Remove your shade setup after seven to ten days so plants can get used to their permanent spot in your yard. Keep watering your new perennials deeply every other day for the first month of their life in the ground. Then taper off as roots spread out and get settled into your garden soil on their own.
You might find a sale too good to pass up or spot the perfect plant at your nursery in July. Pick the right tough plants and give them extra water and shade during that first stretch. Your summer additions can make it through to bloom for you the next year with just a bit of extra attention from you. The key is knowing what works and what doesn't before you dig that first hole.
Read the full article: When to Plant Perennials: Expert Guide
