What to Do in March / April / May

March

• Feed your garden with organic all-purpose plant fertilizer.
• Continue to prepare planting beds for spring:
• Turn the soil and add up to ½ inch of compost.
• Test your soil for pH, nitrogen, phosphorus and potassium and add appropriate fertilizers or supplements.
• Protect sensitive plants from cold injury when frost is predicted.
• Plant vegetable starts once the danger of frost has passed.
• Adjust watering schedules monthly, according to the weather and the changing needs of your plants. 
• Avoid over-irrigation and waterlogged soil. 
• Check your irrigation systems for leaks and broken emitters; perform maintenance as needed.
•  Water if necessary, early in the morning to prevent wet foliage at night. 
• Apply 2-3” of mulch where existing mulch is thin or soil is bare, especially around newly planted trees and shrubs. Keep mulch back 12” from tree trunks and 6” from perennials to discourage pathogens.
• Apply 1” of compost around landscape plants and work in lightly, followed by a layer of mulch. Avoid walking on wet soil. Do not work or dig soil if it is wet.
• Prepare garden tools and pruning shears:
• Sharpen pruning shears and other garden tools as needed. 
• Clean and disinfect your pruning shears after use. 
• Finish with a light coat of oil to protect the blades.
• Manage weeds using non-chemical methods such as cultivation, hand weeding, mulching or mowing; use toxic chemicals as a last resort.
• Cut plants at soil level when half of the blooms have opened, if you planted fava beans as a cover crop in your garden. This will give you the greatest return of nitrogen to your soil.
• Plant gladiolus and dahlia bulbs for summer color. 
• Check nurseries for blooming and budding annuals for spring.
• Consider planting companion plants to provide an environment that welcomes beneficial insects. 
• Select cosmos, marigolds, nasturtiums, sunflowers, zinnias and other beneficials to attract bees.
• Turn compost to keep it as moist as a wrung- out sponge. 
• Add garden waste, grass clippings, pruning material and leaves so long as they are not diseased. 
• Cover compost during rainy weather to avoid the pile becoming waterlogged.

April

• Prune back herbaceous perennials such as salvia to promote plant bushiness.
• Plant edibles such as lettuce, tomatoes, herbs, zucchini and berries. 
• Sow bean, corn, cucumber melon and winter squash seeds directly into the ground. Consider pole beans since they will produce all Spring and Summer and into the Fall. Consider using a soaker hose to conserve water in your vegetable garden.
• Transplant tomato seedlings. Pinch off all but the top two pairs of leaves and set the seedling into a deep hole. Backfill, keeping the top leaves above soil. Tomato roots grow deep (24 inches or more) so make sure roots will have depth to develop.
• Transplant cabbage family vegetables since they will be harvested before July heat.
• Chop cover crops and work them into the soil before they have a chance to seed. They add great organic material that will break down over 2-3 weeks and feed soil.
• Remove aphids from plants with a strong stream of water.
• Pick off cabbage moth eggs, caterpillars, snails and slugs by hand, or use non-toxic slug bait.
• Start planting summer annuals such as lobelia, begonia, marigolds, cosmos, petunias, snapdragon and alyssum.
• Plant gladiolus, dahlias and lilies for summer color.
• Don’t use insecticides in your garden -- you might harm bees and beneficial insects, which help control aphids, mites, whiteflies and other garden pests.

May

• Plant late summer edibles such as pumpkins, squash, sunflowers, peppers, basil and melons.
• Prune spring-flowering shrubs after bloom is past.
• Release ladybugs and other beneficial insects to help control aphids, mites, whiteflies, and other garden pests.
• Let self-seeding annuals go to seed instead of deadheading. 
• Keep your strawberry crop clean by spreading bark mulch around plants, lifting flowers and leaves above the mulch. This also reduces water requirements and cuts down on weeks.
• Harvest radishes when the crown begins to show above the soil. Avoid split radishes by not over-watering.
• Dig new potatoes  as soon as the plants begin to bloom. Start by gently bringing up the soil with a pitchfork about a foot away from the plant. Separate out the tubers by hand.

Dig Deeper:  Spring Edibles

Plan: Develop a garden layout and timetable for cool and warm season crops, taking plant rotation into consideration.  If space is limited and rotation isn’t possible remove sick plants and send them to landfill.

Soil: Prepare your garden plot three weeks before planting. Weed your plot and turn (dig) in any cover crops. Loosen the soil 10-12” deep, breaking up large clods of soil. Add a 1” layer of compost or high quality organic material to the bed, work the amendments into the top 4” of soil. Water the bed evenly without over-wetting; let the bed rest. At the time of planting, add organic fertilizer to the planting hole depending on the feeding needs of your vegetables (light, medium or heavy). Lightly work the fertilizer into the planting hole.

Plant: Check our planting calendars for what to plant and when to plant it in San Mateo County based on conditions (hot, sunny, foggy) in your garden.

Feed Plants:

• Berries, citrus and deciduous fruit trees – feed once
  during spring with an appropriate fertilizer. Carefully follow the application rate for your product -- always spelled out on the back of the box or bag.
• Grapes – feed with an appropriate fertilizer after the vine has blossomed or when grapes are about 1⁄4 inch across; follow application rate for your product.
• Acid-loving fruits – use an acid fertilizer for blueberries, cane berries, raspberries and strawberries; follow application rate for your product

Protect: If a frost is predicted, water citrus, avocado and other frost-sensitive plants; keep the root zone moist but not soggy. Through March, some trees may still need to be covered. If temperatures fall below 50° F, cover outdoor seedlings. In May, fruit trees and grapes can be covered with netting to exclude birds.

Prune: Thin fruit tree blossoms and developing fruit as needed.  Prune table grapes between January and March - Check out the CA Garden Web - Growing grapes in your backyard.

Harvest: Harvest mature cool season vegetables. Not sure if it’s ready to harvest? This link will help. Check the vegetable gardening section of the California Garden Web.

Dig Deeper:  Spring Landscape 

Plant: Perennials, drought-tolerant shrubs. Plant summer-blooming bulbs (callas, cannas, dahlias, gladiolas, etc.) and summer-blooming annual flowers. Frost-tender plants (bougainvillea, hibiscus) can be planted after the last frost.

Feed plants: Determine the nutritional needs (N- P-K and pH) of landscape plants. Determine the timing for repeated application of nutrients and establish a schedule. Follow the application rate for your product.

Protect: If a frost is predicted, water your plants, keeping the root zone moist but not soggy. Cover frost-tender species as appropriate (bougainvillea, hibiscus & succulents).

Propagate: Direct sow summer and fall annuals (cosmos, marigold, nasturtiums, sunflowers, petunia, and zinnias) when soil temperatures reach 70° F. For an early start use a heat mat & grow light to germinate seeds 6-8 weeks before setting out. Harden off plants before transplanting. Sunflowers and nasturtiums do not transplant well. Divide or transplant hardy perennials (aster, chrysanthemum, hosta). Divide spring bulbs (daffodils, Pacific Coast iris, tulips)

Maintenance: Eliminate standing water, e.g. in gutters, drain pipes & flowerpots, to deter mosquitoes. Clean winter debris from ponds, fountains and bird baths. Aerate and fertilize lawn areas (early May); reseed bald patches; start mowing warm-season turf. Replace any undesirable plants in containers and replenish soil, mixing in compost. Inspect for root rot (caused by excessive water and poor drainage).

Prune: Prune dead, diseased, and distorted twigs, stems and branches from winter-flowering shrubs (camellias, rhododendrons). Clean up fallen leaves and blossoms from the area below and around your plants. Do not compost diseased material so that it is not reintroduced into the soil when compost is spread.

Spring Pests and Diseases

Pests

Watch for: 

• Ants, aphids, borers, carpenter bees, mosquitoes, slugs, snails, yellowjackets (March - May); scale (April - May); spider mites (May)
• American plum borer -- Check for frass and gum on lower branch crotches and graft unions of young trees such as almond, mountain ash, olive, sycamore, and stone fruit (April -- May)
• Cherry spotted wing drosophila – Check cherry, raspberry, blackberry, blueberry, and strawberry crops (April - May)
• Clearwing moths – Check for signs of boring in ash, birch, pine, poplar, and willow; less often in oak, sycamore, and stone fruits (April - May)
• Codling moth – Check apple and pear trees (March - May)
• Scab – Check apple, crabapple, and pear trees (March)

Inspect:

• Citrus – Look for Asian citrus psyllid (when new leaves are forming); caterpillars and scales (March-May); mites and thrips (April); leafminer (May)
• Olives – Act to suppress psyllid (March) and fruit fly (April - May); ash borer, psyllid and scales (April - May)
• Roses – Watch for aphids (March - April); hoplia beetle and thrips (March – May)
• Stone fruits – Watch for aphids, borers, caterpillars, and scale insects (March - May)

For further information, refer to UC IPM Pest Notes

Diseases

Watch for:

• Anthracnose (leaf blight) – Check ash and sycamore (March-May)
• Fire blight -- Look for oozing & dead limbs on pome plants such as apple, crabapple, pear & pyracantha (March - May)
• Peach leaf curl – Check peach and nectarine trees (March - April)
• Petal blight – Check azaleas, rhododendron and camellia (March)
• Powdery mildew – Inspect apple, crape myrtle, grape, rose, and stone fruits (March - May)

Inspect:

• Roses – Check for botrytis blight, downy mildew and rust (March - April); black spot, powdery mildew (March - May) 
• Stone fruits – Monitor for disease such as brown rot and powdery mildew (March - May)

For further information, refer to the UC IPM Disease Menu

A portion of this Spring garden checklist was originally developed by Contra Costa County Master Gardeners. Content has been expanded and adapted to San Mateo and San Francisco Counties.