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Weather can be quite random in Portland during April. Hail, then sun, then a warm afternoon followed by a frost at night…hard to predict. Frost is still possible throughout the month and well into May. It is probably still too early to have frost-tender crops out unprotected (basil needs protection). New plantings should always be watered in after planting; don't assume the rain will do it. Though rainfall is usually frequent, don't assume everything is thoroughly watered without at least a glance.
Ladybugs and beneficial nematodes become available in April once the temperatures are warm enough. Ladybugs are natural predators of aphids, whiteflies, and other sucking insect pests. Nematodes are useful for certain soil-borne pests such as crane fly larvae and root weevils.
Many annual flowers are appearing now on our shelves; from cold tolerant pansies and spring flowering bulbs to the first of the summer bloomers. This includes fuchsias, geraniums, alyssum, snapdragons, bacopa, and others. If you haven't done so already, clean up those overwintered beds and containers and start planning and planting. Note that the most cold-sensitive items such as Portulaca and zinnias might need to wait for the warmer temperatures of May to be planted.
April is perennial planting time, no doubt about it. A vast selection of spring bloomers are looking great and ready to go, and many of the summer bloomers are poking their heads up. Some of the most heat-loving perennials are not available yet; you'll have to wait a bit for late blooming Hibiscus or Zaschneria. Additionally, you can divide and separate perennials at this point.
At home, many of your perennials may be growing and/or blooming now, so it is time to be tidying, fertilizing, and watching for pests. Most fertilizers marked as "rose and flower food" or "all-purpose plant food" are great for perennials. Watch out for slugs, cutworms, aphids, and other common pests. You will soon see your first spittlebugs of the year if you grow rosemary but hey, they are mostly harmless. As for the slugs and cutworms, your major symptoms are chunks out of leaves or new shoots cut through. We have treatments for all of these and other garden pests, of course.
If you have not done so already, get those root crops (like onions and potatoes) planted as soon as possible. Brassicas (broccoli, cauliflower, etc.) can be started and grown outdoors in April, along with lettuce, spinach, and most leafy greens. Still be ready to cover with frost blanket just in case of a late cold snap. If you already have some of these early crops that were previously started indoors, be sure to transition them to a cold frame or unheated room/basement window in preparation for planting outside. Gradual temperature changes are the key here, or else the plants might be stunted or fail due to shock.
I'm afraid it's still too early for tomatoes, peppers, melons, and other warm season crops to be outside. These can be started in a heated greenhouse or possibly indoors at this point if you wish to get a jump on summer. Note that melons and squashes are huge growing vines and don't stay tidy on a windowsill very long. Once you are ready to plant these outside (in May or June), follow the same guideline as above for transitioning them, unless the indoor and outdoor temperatures are about equal.
While you are waiting for the temperatures to warm up, you can add organic matter to your veggie beds. Most vegetable crops do best with a lot of organic matter in the soil; manure-based composts are often recommended. Also, regular fertilizer doses (once the crops are growing) are required for most veggies to maximize harvest. Note that different types of fertilizer work in different ways so the definition of "regular" is best found on the packaging of the product you choose.
April is certainly a time to get your lawn in order. Get that moss out, fertilize, and start mowing as necessary. Apply lime if you have not recently. Lawn usually starts growing quickly in April, filling in those patchy parts. This process is slowed if you have a lot of moss or thatch, so de-thatching may be necessary. Thatch is that layer of decaying organic matter that builds up at the soil surface, near the growing shoot of the grass blades. It can be removed when too thick by a thorough raking with a lawn rake.
If your lawn is quite patchy, this is an excellent time to add seed to thicken it up. Keep humans and pets off the sprouting lawn as much as possible. Sod can be laid as an alternative if the grass is pretty bad and you want to start fresh. Either way, loosen the top layer of soil with a rake and mix a thin layer of compost in before you seed or sod.
It is definitely planting time for hardy trees and shrubs, and we have plenty to choose from. Come on down for the best selection of the year on most of these plant types, including fruits.
Some deciduous trees show their best leaf color just as they emerge in spring. While many Japanese maples (Acer palmatum cultivars) are well known for their autumn color, some are absolutely exquisite at first leaf emergence. Katsura (Cercidiphyllum japonica) is another example of this, it being a larger, upright tree. For shrubs, some forms of Spiraea, Sorbaria, and Nandina (Heavenly Bamboo) have great new leaf color.
For existing plantings, now is a good time to start fertilizing as the growing season is underway. Most trees and shrubs are not picky and will do fine with an all-purpose food, although we have specialty foods for acidic soil lovers (rhododendrons, azaleas, dogwoods, camellias, gardenias, etc.) and for fruit vines and trees. Note that older plantings of large shrubs or trees that are thriving anyway probably don't need to be fertilized.
Little pruning is necessary now, the one big exception being spring flowering shrubs. Evergreens such as rhododendron, pieris, and camellia can be pruned after flowering is finished if you are trying to control the size of the shrub. Early flowering deciduous shrubs such as flowering currant and forsythia can also be pruned after bloom if you did not do so in winter.
Aphids might be making their first appearance on your roses, or possibly on some of your street trees. You know there is an aphid infestation on the trees if your car is sticky after parking under the tree overnight. Note that this symptom may not occur as early as April, but the aphids might be there. There are effective insecticides available if you feel treatment is necessary, but it might not be on larger, healthy trees. Note that the quality of your rose's flowers will be much higher if you do keep the aphids away.
The first part of spring can be felt indoors too. The days are longer and your houseplants may be starting to grow a little fuller. Now is a good time to go through and determine whether you need to do any repotting for the upcoming growing season. As the days get longer and hotter, pot-bound plants can dry out too fast or grow spindly. Get some fresh potting soil and larger pots (just one size larger in most cases) and prepare to repot those pot-bound plants. Be sure to water after the up-potting. It is also a good time to start fertilizing your houseplants after their winter rest.
If you have conservatory plants (plants that go outside for the summer) you might start grooming them for their transition outside. Citrus and gardenias can often go outside in April if the night temperatures are not freezing, but other plant types should begin a gradual period of acclimating to outdoor temperatures, with most going outside in May at the earliest. This list includes bougainvillea, hibiscus, and mandevilla. Sometimes it is beneficial to prune these plants once they go outside so that the re-growth is thick, full, and sun-tolerant.
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