Maintenance by The Season
Prune off remaining perennial debris from last fall down to the level of the mulch.
Apply slow release fertilizer pellets to planting beds and gardens.
Apply a soil pH adjuster such as aluminum sulfate or disintegrating sulfur pellets to acid loving plants to keep them healthy in our alkaline soils of southern MN. Plants that will require this are all your evergreens, plus broadleaf evergreens like Rhododendrons, Boxwood, evergreen creeping Euonymous, Pachysandra, Vinca and also acid lovers such as Blue macrophylla Hydrangea, Azaleas, Ilex winterberry, and ferns. Blue Hydrangea will require re-application bi-weekly to keep the blossoms blue instead of pink.
Apply a pre-emergent herbicide (such as Preen) on planting beds and gardens. Keep in mind that this works by preventing germination of seeds, so this will kill not only weed seeds, but flower and vegetable seeds too. Do not use Preen in an area where you want seeds to grow. This generally is effective for 4 weeks, at which time you can re-apply as needed.
Apply a fresh layer of mulch once the ground has thawed to maintain a 3” average depth for optimum weed control.Doing this before the perennials emerge makes the job much easier.
Trim other vines for size control as desired.
Prune dead tips or branches off of roses when the bud out with the first signs of growth. Some top-hardy varieties may die back to the mulch completely if there was no snow cover to protect them. If you see them coming back from the base and they are a hardy rose, simply cut all of the dead branches off and watch them grow and bloom by June anyhow.
Prune dead or broken branches out of evergreens from winter snow damage and prune to shape or control size as well.
This list includes: Arborvitae, Boxwood, Chamaecyparis, Evergreen Euonymous, Fir, Hemlock, Juniper, Larch, Microbiota, Spruce, and Yew. Pines need only be bud pinched if at all possible as the buds emerge to control growth. Only prune back on the branches if the pine has been neglected.
Prune summer flowering shrubs for shape or size control before they leaf out. This list includes: Barberry, Diervilla, Clethra, Cotoneaster, Currant, Dogwood, deciduous Euonymous (burning bush), Honeysuckle, Hydrangea arborescens (white Annabelle type), Hypericum, Ilex (winterberry or Holly), Maple, Ninebark, Potentilla, Sambucus (Elderberry), Smokebush, Snowberry, Sorbaria (false spirea), most spireas, Stephanandra, Sumac, Tamarisk, Viburnum, Willow, and Witch Hazel.
Apply a crabgrass preventer/ fertilizer combo on the lawn areas as the lilac bloom buds are emerging when the soil temperature is at least 50 degrees. Do not apply this for 2 weeks if you have put down grass seed and for 30 days after application, do not apply any grass seed asn the crabgrass preventer is non-selective and kills all seeds.
Plant your annuals, vegetables, and summer flowering bulbs such as gladiolas and dahlias after danger of frost has passed. Generally this is May 20th or later in MN.
Prune spring blooming shrubs for shape and size control within 3 weeks after their blossoms finished. These shrubs set their next year’s bloom buds about 4 weeks after blooming and so pruning in this window prevents cutting off next spring’s blooms. This list includes: Andromeda, Azalea, Chokeberry, Cotinus (smokebush), Daphne, Forsythia, Fothergilla, Blue macrophylla Hydrangea, Lilac, Magnolia, Mockorange, Prunus (sandcherry, plum & almond), Quince, Rhododendron, Serviceberry, spring flowering spirea types such as Snowmound or Bridal Wreath & Renaisssance and Weigelas.
Prune Japanese Tree Lilac, Magnolia and Cercis (redbud) trees only for shape shortly after blooming as they are spring blooming trees and set bloom buds about a month after blossoms finish.
Prune any of the evergreens from the spring pruning list again for size control if desired.
Apply a 2nd lawn fertilizer application roughly 30 days after the first one, but no later than June 21st as the weather will get too hot and the fertilizer may burn your lawn. This is not necessary if you spent extra for a premium slow release fertilizer the first time in May as it will last more than 30 days. If you have dandelions or other broad leaf weeds, use a weed killer/ fertilizer combo.
Maintain your lawn with 1” of water per week preferably with natural rain, but with sprinklers if necessary. Water established trees and shrubs only if we get drought conditions or if they show water stress.
After the scorching summer heat breaks, usually the last week in August or first week in September, apply a lawn fertilizer.
Four weeks later, apply a winterizer lawn fertilizer.
Dig those summer flowering bulbs out (they aren’t winter hardy) and store them in a cool dry and dark location for the winter.
Plant winter hardy spring flowering bulbs now such as crocus, daffodils, hyacinths, tulips, scillia and squill. You may leave them in the ground permanently although they often don’t flower as well in subsequent seasons. Some varieties, however, do very well and prosper and even naturalize with age.
If you prefer not to wait until spring, you may apply a fresh layer of mulch now to maintain a 3” depth for optimum weed control. Especially if your mulch is thin now, this will protect your perennials from winter dehydration and damage.
Cut off most of the perennials down to the level of the mulch once a killing frost has occurred and their foliage has turned brown which is a sign of dormancy. Leave those which provide winter interest from their tall thick stems or interesting seed heads. The perennials you may consider leaving until spring because of their winter beauty are: all ornamental grasses, achillea moonshine or coronation gold, aconitum, actaea or cimicifuga, aquilegia, asclepias, astilbe, astrantia, aster, baptisia, centaurea, chelone, fall blooming clematis, coreopsis grandiflora, dendranthema, dictamnus, digitalis, echinacea, echinops, epimedium, eupatorium, filipendula, gaillardia, gypsophila paniculata, heliopsis, hibiscus, liatris, leucanthemum, lobelia, lupinus, papaver, penstemon, perovskia, phlox (upright types), rudbeckia, sedum (fall blooming types), tanacetum and veronica.
Some perennials are evergreen and semi-evergreen and should not be cut back at all, although you may remove any damaged tissue in the spring. These include: armeria, asarum ginger, bergenia, cerastium, creeping phlox, dianthus sweet william, gallium sweet woodruff, hellebores, heuchera, iberis, lamium, pachysandra, stachys, lavender and vinca minor.
Prune oaks in January or February as it is the only time when they can be pruned safely without a chance for spreading diseases.
Prune Maples and crabapples in March.
Prune most deciduous trees in late winter (February-March). Do not trim Magnolia, Japanese tree Lilac or Redbud until summer.
Get a head start on spring by pruning the summer flowering shrubs on a nice winter day. See the list under the spring category.