9 Perennials You Should Fertilize in March

Fertilizers add extra nutrients to the soil so your plants can easily absorb them. The most important nutrients for plants are the macronutrients nitrogen, phosphorus, and potassium, or NPK. These nutrients improve the plant’s roots, cell membranes, and overall structure.  

Some perennials, like coneflowers and hostas, respond well to a light application of compost once a year. Others, however, benefit from plant food as soon as spring arrives. With the extra boost in nutrients, these plants will put on vigorous new growth just in time for summer.

Start this year’s gardening season by giving your heavy-feeding varieties an extra energy boost. Below are nine perennials you should fertilize in March for abundant blooms. 

Langbeinite

Our Rating

Potassium Boost: Langbeinite

View at Epic Gardening

Espoma Bio-tone Starter

Our Rating

Espoma Bio-tone Starter Plus

View at Epic Gardening

Garden Sulfur

Our Rating

Lower PH: Garden Sulfur

View at Epic Gardening

Roses

	botanical name Rosa spp.
	sun requirements Full sun to partial shade
	height 1-60’
	hardiness zones 2-11

Roses are some of the most popular perennials worldwide. Because of their gorgeous and aromatic blooms, they need quite a lot of food. These perennial shrubs are some of the biggest heavy feeders in your garden and March is the perfect time to fertilize them with the nutrients they deserve.

For established roses, use an organic fertilizer specifically made for them. Slow-release, granular fertilizers work the best. These formulas let the nutrients out slowly over time, providing continuous feeding as your plant puts on new growth. 

Follow the directions on the packet and avoid fertilizing directly on the plant. Cover the top of the soil around the plant and gently water it. The fertilizer will absorb into the soil and give your flower the energy it needs to put on magnificent blooms. 

Garden Phlox

	botanical name Phlox paniculata
	sun requirements Full sun to partial shade
	height 2-4’
	hardiness zones 4-8

Garden phlox puts on a show of stunning pink and white flowers. It blooms in the early summer in zones 4 through 8 and lasts through the summer. To get the most out of its radiant flowers and upright structure, try fertilizing it in March. 

Just before the plant puts on new growth, add a little organic granular fertilizer to the soil. Follow the application directions on your product. Gently apply the fertilizer around your garden phlox, without touching the plant. Water around the soil so the fertilizer absorbs into it evenly. 

This should be the only application your plant will need until the following spring. Add a generous amount of organic compost in addition to the macro nutrient boost. The extra compost will improve the soil and add micro nutrients your garden phlox will love. 

Astilbe

	botanical name Astilbe spp.
	sun requirements Partial to full shade
	height 1-4’
	hardiness zones 4-9

Astilbe is a heavy feeding herbaceous perennial. It puts on large dark green fern-like leaves and colorful feathery blooms. They need a lot of nutrients throughout the year to thrive. 

Start their feeding schedule in March or later in spring once the ground unfreezes. Use a fertilizer that’s a little heavier in nitrogen, like a 3-1-2 NPK ratio. Your astilbe will need the extra nitrogen to put on tons of lush foliage in time for summer. 

Some varieties bloom in late spring while others show their magnificent colors in early summer. Throughout the year, add plenty of compost and organic material to encourage it to flourish. 

Clematis

	botanical name Clematis spp
	sun requirements Full sun to partial shade
	height Up to 30’
	hardiness zones 3-9

Clematis flowers are beautiful flowering vines in the buttercup family of plants. They put on tons of growth in spring, producing colorful blooms that climb up structures and trees. Some varieties stay manageable in size while others spread up to 30 feet. 

To get to their impressive size and produce abundant flowers, they need a lot of extra nutrients. In warmer climates in March, fertilize this perennial with a balanced blend. Work it into the soil and give your plants a little extra water. Continue feeding them with organic compost every month or two. 

Once these flowering vines start blooming, switch to a low nitrogen fertilizer. The plants use nitrogen to produce foliage instead of flowers. 

Hibiscus

	botanical name Hibiscus spp.
	sun requirements Full sun
	height 2-16’
	hardiness zones 4-9 for deciduous species and 9-12 for Tropical Species

There are over 200 species of hibiscus, ranging from colorful tropical evergreens to deciduous perennials. Throughout the growing season, they put on an impressive show of multi-colored flowers. Some can grow to over 12 inches in diameter. Along with their stunning blooms, hibiscus plants grow tons of dense foliage, making them perfect for hedging. 

These plants need a lot of extra nutrients to put on impressive growth. It’s important to start feeding them as early as you can, usually around March. You’ll continue a regular feeding schedule throughout the growing season. 

Apply a generous amount of organic fertilizer to the soil and water thoroughly. Always follow the product’s directions to avoid overfeeding. In March, fertilize this perennial with a product high in nitrogen and potassium. Nitrogen will boost productivity in foliage growth while potassium helps photosynthesis. 

Bougainvillea

	botanical name Bougainvillea spp.
	sun requirements Full sun
	height Up to 40’
	hardiness zones 9-11

Bougainvillea are impressive tropical vines that you can form into colorful hedges. They produce radiant bracts that enclose tiny flowers. The bracts come in multiple colors, including red, orange, yellow, pink, purple, and white. Besides their colorful blooms, these plants produce large oval leaves that provide a beautiful backdrop to their colorful bracts. 

To get gorgeous bougainvillea, start fertilizing in March, just before the plant puts on new growth. Start with a nitrogen rich fertilizer to get dense new foliage growth before summer. Follow up with a plant food rich in potassium in late spring and early summer. This will kick start their production of flowers and bracts. 

If you have young plants, start with a balanced fertilizer with a NPK ratio of 10-10-10 or similar. Balanced macro nutrients help young plants put on healthy, even growth from their roots to their leaves. 

Artichoke

	botanical name Cynara cardunculus var. scolymus
	sun requirements Full sun
	height 3-5’
	hardiness zones 7-10

Artichokes are some of my favorite edible perennials to grow. Besides their delicious flower buds, I love their spectacular serrated leaves and beautiful purple to violet flowers. When they bloom, they almost look otherworldly. 

Whether you’re growing your artichokes for food or their impressive flowers, you’ll need to give them a healthy amount of nutrients. Start in spring by adding a liquid fertilizer such as a liquid fish fertilizer to boost nitrogen. Keep applying nitrogen-rich fertilizer every other week. 

Once the flowers form, switch up your fertilizer to a plant food high in phosphorus. This will give your plants extra fuel for developing their edible flower buds.

Bearded Iris

	botanical name Iris x germanica
	sun requirements Full sun to partial shade
	height Up to 30”
	hardiness zones 3-9

Bearded Irises are perennial flowers that are some of the first bloomers in spring. They can sometimes put on incredible shows of color in both spring and fall. In winter, they go dormant again until the soil warms up and they reemerge. 

To get big, beautiful blooms in spring, give your bearded iris plants enough fertilizer just after they bloom in spring. Irises respond to organic fertilizers higher in phosphorous like bone meal. These products supply bulbs like irises with the nutrients they need to produce their gorgeous blooms. 

Water your plants well immediately after applying a bone meal fertilizer. The bone meal will release its nutrients slowly, which your plants will absorb through the soil. Follow up with a light application of organic compost and your perennial irises will be very happy. 

Jacob’s Ladder

	botanical name Polemonium caeruleum
	sun requirements Full sun to partial shade
	height 1-2’
	hardiness zones 4-9

Jacob’s Ladder is one of my favorite perennial flowers. Although this perennial is not a heavy feeder, it does benefit from fertilizing in March, just before it puts on new growth. 

Feed this aromatic flower with a balanced organic fertilizer. This will help encourage vigorous new growth and its signature ladder-like structure. By mid summer, you’ll have gorgeous purple bell-shaped flowers popping up everywhere. 

After spring feeding, your flowering perennial won’t need fertilizer until its flowers fade and you cut them back. This will hopefully get the plant to produce another round of blooms in late summer and early fall. Some gardeners choose to apply layers of compost for similar results.