March Garden Tasks

March is a transitional month when the promise of spring is mixed with the probability of frost. Don’t let your cabin fever get the best of you. Frosts are possible until well into April and rainy winter weather can still leave soil too damp to work. Remember to check the soil by taking a handful of soil and molding it into a ball in your hand and then drop it to the soil bed from 2 feet above. If it breaks apart your soil is dry enough to work. The following are some reminders of things you can be doing in the Month of March!

Flower Garden

  • Start seeds of annuals (and plants grown as annuals) indoors: Ageratums, annual asters, celosia (cockscomb), Chinese lanterns, annual chrysanthemums, tuberous begonias, cornflower (bacchelor’s buttons), cosmosdahlias, gazania, globe amaranth, annual hollyhock, marigolds, nasturtiums, flowering tobacco, petunias, annual phlox, portulaca, annual salvias, annual scabiosa, snapdragons, statice, stock, strawflower, sweet allysum, verbena, & zinnias.
  • Plant sweet peas. For wonderful fragrance plant sweet peas from the middle to the end of the month. Soak seeds overnight in luke warm water to promote germination. Provide a trellis or other support for the plants to grow up.
  • Begin planting dahlia and iris as well as other summer flowering corms bulbs and tubers. Dahlias and Iris are some of the earliest to arrive at garden centers.
  • Divide perennials that flower in summer or fall now. You can tell perennials need dividing when the center becomes less vigorous or die out.
  • Prune summer and fall flowering clematis. These clematis produce flowering buds on new wood and can be pruned now to the strongest canes. Spring flowering clematis should be pruned right after they flower.
  • Clean up perennials and cut back ornamental grasses to a few inches above the ground to make way for new growth.
  • Fertilize and prune roses. The rosarian’s organic fertilizer of choice is alfalfa. It can be found at your garden center as alfalfa meal or in bulk at a feed store. You don’t have to pay extra for vitamins added though.  For my roses I use Organic Roses & Flowering Shrub Fertilizer Spikes.  Prune away any cold injury to canes. Prune back to a healthy outward facing bud. Complete all your pruning activities before the buds break.

General Landscaping

  • Get your soil tested. It is a good idea to have your soil tested before fertilizing plants in your home landscape. Testing for Nitrogen, Phosphorus and Potassium and pH is all that is necessary for the average homeowner. Home soil test kits are available online or at you local garden center. But if your plants are unhealthy and you can’t pinpoint the cause you may want to consider sending your soil out to be tested. Test for the primary nutrients (Nitrogen, Phosphorus and Potassium) as well as the secondary nutrients (Calcium, Magnesium, Sulfur) and micronutrients (Boron, Copper, Chlorine, Iron, Manganese, Molybdenum, and Zinc).
  • Add appropriate fertilizers. Base your fertilizer selections on your soil tests and needs of your plants. I prefer organic or a combination of small amounts of fast acting inorganic fertilizer in the spring as well as slow acting long lasting organic fertilizers that will continue to feed into the fall as they slowly decompose. Organic fertilizers feed your soil first and then your soil feeds your plants.
  • Set out natural slug bait. I prefer safe slug bait made from iron phosphate because it is nontoxic to non-target animals including pets. You will start to see more slug activity this month as they become more active.
  • Get a jump start on weeds. You may not have been working out in the garden but the cool weather weeds have already been busy. Pull weeds like shot weed before they finish seeding to reduce next years weeding chores.

Indoor Garden

  • Increase fertilization and water of indoor plants. This increase in water and fertilizer coincides with the increased light levels as the sun moves southward and more directly into windows. This increases the plants transpiration of water and increases their growth rate.
  • Repot root bound plants. If plant lacks vigor, roots are coming out of drainage holes or if water drains through the plant before it can absorb the water it is more than likely time to transplant. Move up 2 inches in pot size.
  • Pinch and prune houseplants. Just like outdoor plants the best time to prune is in early spring just before new growth starts.

Insect (pest) Alert
Slug activity is increasing as temperatures increase. Continue to monitor them and use iron phosphate slug baits if you see any damage.

Pollinator alert
The earliest of the pollinators will be out this month in time to work on those early flowering trees and shrubs. The earliest is the Orchard Mason Bee, which are solitary – non-stinging native bees. A good indicator shrub for their emergence is the blooming of Andromeda (Pieris japonica). They are perfect for making sure your early flowering fruit trees and shrubs are pollinated. If you don’t have any local resident orchard bees you can get them at many garden centers this spring or through mail order in the internet (

Vegetables, Herbs & Fruit

  • Early in the month is the last chance for dormant pruning fruit trees. You still have some time to prune back diseased wood, water sprouts (suckers) and crossing limbs. Don’t prune back fruiting spurs unless you are intentionally thinning them out.
  • Last chance for dormant oil sprays of fruit trees. Fruit trees like apples and pears benefit from dormant oil sprays which help to control (by smothering) sucking insects like aphids, scale, spider mites, thrips to name a few. Don’t apply after any buds have broken because dormant oil spays (unless it is an all season oil spray) are more concentrated than summer oil sprays and can burn new growth.
  • There is still time to start spring vegetable seedlings indoors.  Broccoli, Brussels sprouts, cabbage cauliflower, celery and celeriac and indoors on a windowsill, greenhouse or under grow lights.
  • Mid month start planting warm weather vegetables like eggplant, tomatoes, peppers, potatoes (from true seed).
  • Transplant fruit trees purchased from your favorite grower should be planted now as dormant bare root plants.
  • Wrap early flowering dwarf fruit trees if frost threatens. If you have had years where your plums and peaches have not set fruit it could be because a late frost knocked them out. If the forecast calls for below freezing weather and the flower buds are already breaking wrap the trees in reemay (spun polyester garden cover) to protect them over night.
  • Sow seeds outdoors when soil temperatures are at or above appropriate minimum temperatures: lettuce (40°F), peas (40°F), Swiss chard & beets (40°F), carrots (40°F), leeks (45°F), onion (45°F), spinach (45°F), turnips (50°F), radishes (50°F) and Asian greens (50°F). Test soil temperatures with a soil thermometer.
  • Plant seed potatoes (from potato sections not to be confused with “true seed” which is started indoors like tomatoes) and onion sets, shallot sets, and garlic cloves (results in smaller bulbs then when planted in fall).
  • Start Herb seeds indoors: marjoram, summer savory, chives, fennel, parsley, basil, anise hyssop, perilla, lemon balm, & sorrel.