When to Water
For the first month after the initial planting, you should water once or twice a week. However, this is dependent on the amount of rainfall.
How to Water
Watering should be done in the morning. Foliage should be dry before nightfall. Wet foliage makes the perennial more susceptible to disease organisms. Hand water or use a soaker hose. The hose should be laid out permanently in the bed. Although this may make it difficult to cultivate around, you will be disturbing the plants and beds less than with continued movement of a hose. Water at a low level, keeping the foliage as dry as possible.
Mulching has many positive benefits for your perennials. Mulching acts as a protective blanket for your perennial's roots. It holds in moisture cooling the roots, reduces the need for watering, promotes root growth, enriching the soil as it decomposes as well as improving the soil structure. Mulch reduces the light reaching the soil surface which suppresses weed seed germination. If some weeds should happen to root themselves in the mulch, they are easier to pull.
How to Mulch
A 2-3" thick layer should be maintained. However, don't pack the mulch closely around the crown or base of the perennial. This could promote rotting. (Note: bearded iris prefer no mulch.)
When to Mulch
Immediately after planting the perennial, reapplying in early spring as needed.
Why is this Necessary?
A winter cover helps keep the soil temperature from fluctuating over the winter months. This prevents the plants from being heaved out of the soil by the freeze/thaw cycle.
What Should be Covered?
• Newly planted perennials
• Shallow rooted perennials such as mums, shasta daisies and delphiniums
Non-matting materials such as: marsh hay, evergreen boughs, pine needles, leaves, straw.
How and When to Apply
Many sources recommend removing the dead foliage at the end of the growing season before you cover the perennials. It is thought that it may harbor disease and insects. If you enjoy seeing the attractive fruit/seed heads through the snow, you may want to leave the showier ones (like autumn joy sedum and ornamental grasses, etc.) intact. Some seeds are enjoyed by the birds that migrate through and that stay into the winter.
Generally around Thanksgiving or when the soil is thoroughly frozen to a depth of 2", you may start covering. Caution, covering before this time is not recommended as it could provide a winter haven for rodents with your perennials a good source of food. You should check the perennials regularly to see if they have been disturbed by frost heave. If so, firm them back into the ground.
Remove the winter covering in early spring.
Spring is the time to apply fertilizer. Sprinkle a balanced bedding plant fertilizer throughout the bed. Slow release or water insoluble nitrogen is preferred early in the season. If a plant needs immediate nourishment, a liquid foliar feeding may be applied at half strength. This is used almost immediately and lasts 7-10 days. Follow manufacturer instructions for application rates.
After a few years, some perennials tend to lose vigor and need to be rejuvenated. Dividing is the best way to accomplish this. This can also be helpful if a particular perennial is getting too large for its garden space or if you would like to introduce this plant in another area of your yard. In general if a plant is growing well and not crowding, division is not necessary.
Most Perennials Can Be Divided
It is especially beneficial to divide iris, daylilies and lilies after 3 years. Coralbells (Heuchera) tend to grow out of the ground and so should be divided and replanted deeper. Some perennials can obtain a large spread while the center can often lose vigor and die out. To remedy this, cut a section out of the center, fill with new soil and plant a small division from the outside of the clump. Monarda is a good example of a plant that does this.
When to Divide
Early spring when the plants are only about 2-3" high or in fall when the foliage starts to die back.
How to Divide
Division is made easier by watering the planting bed well a few days before you prune back the perennials (at least 6" above the ground). Dig the entire clump out if possible. Pulling the clump apart is less stressful on the roots than severing them. For large clumps the technique often used is 2 pitchforks set back to back within the root ball then squeeze the handles together as you pry apart the roots. Add fertilizer to the hole and replant a portion of your division.
Staking, Pinching Back, Dead Heading
This is sometimes necessary for tall plants or plants in windy or shaded sites with rich soil. There are a variety of supports which can be used, depending on the weight and mass of the perennial to be supported. It is best to put the stake in place as soon as growth starts in the spring. Some staking can be avoided if enough perennials of similar or slightly smaller size are there to help support one another within the border.
This is used to promote a bushier, shorter perennial. Tips of the growing shoots should be removed in May or June. Following are a few perennials which can be especially benefited by pinching back:
• Obedient Plant (Physotegia)
• Border Phlox
This is removal of dead or spent blooms. It is mainly done for aesthetic reasons or to keep the perennial from setting seed. Perennials benefiting from this technique are:
• Shasta Daisies