April Growing Tips
By Raintree Horticulturist Theresa Knutsen
- Planting in Cold or Warm Spring Weather
- Non-dormant potted plants care
- Frequently asked question - What do I do with plants I can not plant right away
- Insect/Disease Control
- Codling Moth
- Apple Maggot
- Tree Fruit Fungal Diseases
- Fertilizing & Weed Control
- Container Plant Care
- Spring Flower Processing (2 elderflower fritter recipes)
- Spring Grafting Tips
So long as the ground is not under water or water-logged, frozen, or covered with snow, and the weather is above freezing when you plant, you can plant dormant potted or bare root plants. For optimal results planting bare root plants, day time temperatures should be below the mid-60's for several weeks following planting (to give roots time to establish before top growth becomes too demanding). Follow the basic planting instructions in the Raintree Owners Manual we send with each order. If you did not receive one, or have misplaced it, you can also view it on our website: click on Growers Info, then select owners manual.
Planting In Cold Climates:
If you live in an area that is still experiencing winter weather, bare root plants that are still dormant when received can tolerate brief exposure to temperatures down to the lower 20's after they are planted. If you are not ready to plant when you receive your order, refer to the front page of the Raintree Plant Owners Manual which is included with each order or can be found on the Raintree website.
Planting In Warm Climates:
Those of you living in the southern and southeast U.S. may be regularly experiencing day time temperatures in the 70's. If this is the only time you can acquire particular plants, follow the 'Hot Weather' planting instructions in the Raintree Nursery Owners Manual or the following tips to ensure success with your new plants, or pre-order plants to be shipped to you at your optimal planting time early next spring. If your day time temperatures are regularly in the 80's plan to receive bare root plants next season.
1) If you choose to plant out in a permanent location right away, mulch the soil surface well after planting, irrigate regularly to keep the soil evenly moist, not soppy wet, and provide shade until the plants are well-established. Warm air temperatures encourage faster shoot growth than root growth in the cool soil, creating water stress in the tree. Shade helps to reduce the water needs of the plant and give the root system time to catch up with the top of the plant. Follow the same techniques when planting out our dormant potted plants. Providing shade when planting will help these plants adjust to the change in environment.
2) Plant your new plants in a temporary, shady location, mulch, and water regularly through the summer. In the fall, when the worst of the summer heat has passed, move the plants to their permanent location. By the following spring they will be well-established and ready to perform.
3) Plant your new plants in containers, if receiving potted put in somewhat larger containers, maintain them in a protected location, and plant in their permanent location in the fall when the worst of the summer heat has passed.
Non-Dormant Hardy Potted Plants Care:
Sometimes you might receive cold hardy plants that are no longer dormant but you are still experiencing winter conditions. Our hardy plant greenhouses are kept to a minimum of about 28-30 degrees F at night, but late winter or early spring day time sun can warm them up well into the 70's. The resultant new growth is tender and can be damaged by freezing weather, especially below 28º F for more than a couple of hours. Most plants will put on a second flush of new growth after early frost damage, in about 4-6 weeks. To prevent frost damage on non-dormant potted plants you have received here are a couple of options:
Keep the plants where they will receive bright light and remain cool, but above freezing, until danger of frost is past. If you can keep the plants cool (32-50ºF) their growth will be slowed down, so they won't stretch as much, and the leaves will be a little tougher. Fertilize them lightly with a low to medium nitrogen fertilizer, such as fish fertilizer with kelp to supply micro nutrients, or maybe compost tea. The kelp fertilizer may improve plant tolerance to cold temperatures.
As the day time temperature you are holding your plants at increases so will the rate of growth of your plants. Provide supplemental light if the plants seem to be stretching or getting leggy, fertilize lightly as above.
If you are expecting night time temperatures to be mostly above freezing, with an occasional frost still possible, then you could go ahead and plant outside. Be prepared to put some frost protection over your new plants if necessary. A paper bag, spun-bonded floating row cover (such as Reemay), or a blanket (with support) will provide a couple degrees of protection.
Plants that have been actively growing indoors need to gradually get used to being outside in the direct sun and wind to continue to perform their best. Put them outside in a partially sunny location for a few hours a couple of days, and over the rest of the week gradually increase the time and decrease the shade until they spend the full day outside. Then plant following instructions in the Raintree Nursery Owners Manual.
What do I do if my plants have come but I can't plant right away? The goal is to keep the bare root plants cool and dormant, and protect the roots from freezing or drying out. You can generally hold the plants up to two weeks in the bags they arrived in, in a cool (35-45º F) location. Check the bags for moisture a couple times, the shredded paper around the roots should be moist and there should be humidity present on the inside of the bag, standing water more than a 1/2 inch or so is undesirable. Alternatively, you can heel (temporarily plant) the dormant plants in a loose pile of soil or compost outdoors (in the shade if temperatures are on the warmer side) until you are ready to plant. Potted dormant plants (evergreen or deciduous) can also be held in a cool location, or buried outdoors, to the rim of the pot, in the compost pile. Potted hardy plants that are showing new growth are no longer dormant, and that new tender growth will probably be damaged by temperatures below 30-32ºF. Keep them in a cool (35-60ºF) but bright location to slow new growth until most danger of frost is past, harden them off, and plant. If late frost threatens, you can provide temporary cover to protect them. If the new growth is damaged by cold temperatures another flush of growth generally occurs within a few weeks. Hold frost tender plants at a moderate temperature, 50-65ºF, with bright light, until all danger of frost has passed before taking them outside for the summer.
Some of last years tent caterpillars or leaf rollers may have over-wintered in your trees. As spring weather begins to dominate (usually April in the Pacific Northwest) check your trees regularly, a BT (Bacillus thuringiensis) spray is an effective organic control to use when you start seeing the caterpillars.
Codling Moth and Apple Maggot adults will soon be emerging from their over-wintering cocoons in the soil, usually coinciding with the initiation of new fruits on the apple trees. Now is a good time to prepare for monitoring coddling moth and apple maggot populations. Prior to petal fall in apples and Asian pears, install codling moth and apple maggot traps to monitor populations of both insects; #T161 and #T163.
Codling moth adult numbers usually start to increase at petal fall. Apply sprays when the number of codling moths you see in the traps suddenly increases. See Plant Owners Manual page 16 for spray suggestions, or ask for control recommendations at your local co-operative extension service (find yours in the useful links page, after clicking on Growing Info in the top tool bar).
You don't like spraying? The new heavier weave Apple maggot control bags (#T167) we are offering this year may also help prevent codling moth larva from entering the fruit; if the bags go on the fruit early enough (with or before the increase in adult numbers), and the little caterpillar can't chew its way in. According to the Home Orchard Society of Oregon there is a way to improve codling moth control using the apple maggot control bags. Before you install the bags soak them in Surround®, a kaolin clay based insecticide. Here are their instructions:
Materials needed: 4 quart pan, colander to hold apple maggot control bags, another pan (similar volume) to catch the fluid, two pkgs of apple maggot control bags (#T167) so you have 288 bags.
- Put 3 tbsp of Surround® in 3 quarts of water. Start with a small amount of water to make a slurry, then add the rest of the water.
- Stir until the Surround® is fully dissolved.
- Place 288 apple maggot control bags in the mixture-stir to soak the bags.
- Pour the apple maggot control bags and mixture into the colander, with the second container underneath to catch the fluid.
- Stir the collected mixture and pour over the bags in the colander, with the empty container beneath.
- Repeat step 5 until the fluid runs clear.
- Dry the bags by spreading on a wire mesh, the table, etc.
- Install the bags over the little fruitlets before the codling moth starts depositing eggs. (See the installation instructions below in the apple maggot section).
Biological codling moth controls, such as Trichogramma wasps, are available through Arbico Organics (arbico-organics.com). Trichogamma wasps deposit their eggs in the eggs of codling moths and other harmful moths. Put some cards out 7-14 days after you start seeing codling moth adults in your traps, and again every 7-10 days until you no longer see adult moths. An image search on the internet will provide you with pictures if you are not sure what codling moth or apple maggot adults look like.
There are several strategies you can use for Apple Maggot Control; combining strategies can improve your results.
Put out Apple maggot traps with pheromones (#T163) to monitor when the apple maggot flies are present, so you know when to apply sprays. Use 1-3 spheres per tree, increase the number to 5-10 per tree (more in larger sized trees) to trap more adult flies and reduce the apple maggot fly population in your trees.
Thin apple and Asian pear fruit when the fruits are about the size of a dime to a nickel to one fruit every 6-8 inches along the branch and install apple maggot control bags (#T167) to prevent apple maggot flies from depositing their eggs on the fruit. Slip a bag over the little fruit and twist the mouth of the bag around the fruit stem to secure. Each fruit will grow inside the nylon mesh bag and be protected.
If you had a lot of apple maggot flies last year you might try controlling them before they emerge from their over-wintering stage. Treat the ground under your fruit trees with predatory beneficial nematodes available through Arbico Organics. Predatory nematodes actively seek and feed on apple maggot larvae, codling moth larvae, and other harmful grubs in the soil, reducing the number of adults that can emerge and deposit eggs on your fruit. Apply the nematodes in late spring before the adults have emerged, or in fall after fruit harvest. The ground must be moist and night temperatures consistently above 40ºF when the nematodes are applied.
Fungus Control continues in the Pacific Northwest. Spring time warm wet rains encourage the germination and growth of fungal infections in our fruit trees. Continue applying fungicide sprays for scab or powdery mildew in your apples or pears, or brown rot or coryneum blight in your stone fruits if you noticed problems last year. If you are not sure what the problem was take a sample to your local co-operative extension office for identification help. Applying fungicide sprays prior to infection can help keep fungal diseases under control. Fungal diseases are generally more difficult to manage after infection has occurred. Lime sulfur, wettable sulfur, or fixed copper are possible products to use (always follow label instructions), see the Raintree Plant Owners Manual page 16 for more specific information, and page 23 for a calendar of monthly reminders.
Apple and Pear Scab control usually requires several applications of fungicide at two week intervals for complete effectiveness, starting at the green tip or pre-pink blossom stage, or when day time temperatures are above 45ºF. A mixture of delayed dormant (light weight) oil, lime sulfur, and Dipel (a Bt thuriengensis bacterial insecticide) applied as the first leaves start to pull away from the flower clusters will serve as your first spray for scab, powdery mildew, and leaf rollers control. If your spring continues to be wet and cool additional sprays of lime sulfur at the pink stage and petal fall will be needed. You can reduce the number of sprays required to control scab, or increase the effectiveness of your sprays, by paying attention to temperature and moisture patterns, which allows you to forecast when it is time to spray. For more details you can read about this approach in "The Apple Grower" by Michael Phillips, item #S005, or ask about a bulletin at your co-operative extension office.
Stone fruit (apricot, peach, plum, cherry) brown rot and coryneum blight infections occur as buds are swelling. Apply lime sulfur, wettable sulfur, or copper sprays at the ‘popcorn stage' (flower buds look like kernels of popcorn), petal fall, and one week later if the weather continues to be quite wet. Spray times will vary by type and variety, so keep an eye on each tree.
Fertilize: Apply a 1/2 strength dose of fertilizer to acid loving plants, such as blueberries, lingonberries and cranberries as buds start to swell on the plants. Use a fertilizer that is specifically for blueberry or rhododendron. Follow with a light mulch of wood chips or pine needles under the blueberries. Apply a second 1/2 dose of fertilizer when the flowers fall. Raspberries and rhubarb appreciate a mulch of cow or steer manure applied before new growth emerges in the spring. A one inch layer of compost spread under the edge of the leaf canopy of most fruiting plants will help maintain fertility. If your plants seem less vigorous than they should be, a little fish fertilizer with kelp (seaweed) may be helpful.
Weeds: Keep weeds controlled around trees and shrubs, especially those that were planted within the last few years. Be careful when working around blueberries, their shallow roots are easily damaged by vigorous digging and weed removal. If your blueberries have a lot of weeds under them you might try cutting the weeds to the ground, putting down a 1/2 -1" layer of peat moss, several layers of newspaper or a layer of cardboard, and then wood chips on top. Most weeds will be smothered. More persistent perennials that eventually come back through the mulch, can be repeatedly cut off (every 10-14 days) until their roots starve out.
New plantings of ground covers, such as cranberry, lingonberry, or wintergreen, need regular weeding. Even after they have filled the space, some weeds may still come through. Installing Biodegradable mulch (#T435 or #T445) at the time of planting will help control weeds until your groundcovers are established. Make a slit in the 4' wide sheet and plant. This mulch is not porous, so make sure you provide water where the plants are, until the mulch biodegrades (1-2 years depending on product and conditions). A layer of wood chips or pine needles will hide the black color. You could also put down cardboard or layers of newspaper covered with mulch between the new plants to help reduce weeds and contribute to building the soil organic matter.
Permanent weed barrier fabrics may seem to be a good solution for controlling weeds, but only if used for just a year or two, or only just near the trunk of the tree. Longer use in the active root zone area of the plant interferes with organic matter rebuilding in the soil, which can have a negative impact on the general health of your trees. Instead try our Biodegradable mulch 4' squares (#T440) under your newly planted trees to keep grass and weeds from competing until those new trees are established (2-3 years). Top with bark mulch to keep it looking nice as well.
Observe: If you have had problems with adequate pollination or fruit set in the past, the following are some factors to consider. Look at your fruiting plants as they come into bloom, especially those that did not set fruit well last year. Are you seeing maby, or just a few flowers. If there are only a few, did the tree produce a lot of fruit the previous year? Or do the trees receive enough shade in July or August to reduce their time in direct sun to less than 8 hours? Notice if there are plenty of bees in the flowers. If you have bees and flowers, are the varieties that should be providing pollen for each other blooming at the same time? What is the weather doing? Is there a lot of cool wet weather that will support brown rot disease in the blossoms, effectively interfering with pollination? Frost can cause physical damage that interferes with pollination, or provide a site for a secondary infection that damages the flower. Sometimes misting overnight or smudge pots are used to protect blossoms from frost damage. Another possible technique is to run a string of outdoor Christmas lights in the tree, and turn them on when hard frost threatens.
Do you see ants or earwigs in the flowers? Both insects can cause significant damage and interfere with fruit set. If you are growing kiwi, look at the blossoms and compare them to the pictures in our catalog. Make sure you have both male and female flowers.
Daffodil and Tulip Care: Remove daffodil and tulip foliage six weeks after flowering, or when the foliage has yellowed. Don't braid, rubberband, or otherwise mutilate the foliage- the green leaves are feeding the bulb for next years bloom.
As the time approaches for putting frost tender house-bound potted plants back outside (such as citrus, stevia, or lemon grass), keep an eye on the weather, be patient, and wait until all danger of frost is past. For optimal performance avoid exposure to temperatures below 50ºF for more than a few hours. Harden off plants for a smooth transition to outside living. Put them outside in a shaded location for a couple of hours the first day, and over the next week or so gradually increase the amount of sun exposure and length of time they are outside. Continue fertilizing at the late winter/early spring rate of 1/2 the recommended rate on the label while plants are inside or in transition. When they are outside and actively growing, fertilize at full strength. Remember to monitor for presence of unwelcome insects. Early treatment will prevent heavy infestations later.
Start fertilizing your outdoor container plants as their buds begin to swell. If you are using a liquid fertilizer, at first use 1/2 the recommended rate on the label, once a week or so. As your outdoor temperatures increase and roots are able to absorb nutrients more readily, you can increase to a standard dose.
Select a fertilizer that is appropriate for the plant you are growing to achieve optimal performance in the container. Use citrus fertilizer for citrus plants, and blueberry/rhododendron fertilizer for vacciniums (blueberry, huckleberry, lingonberry, and cranberry). For Bananas, encourage lots of vigorous growth initially with a foliage supportive formula that has a high nitrogen content relative to the phosphorous and potassium. When your plant is well established, after 2-3 months, switch to a formula that is higher in phosphorous (a bloom fertilizer) to encourage flower and fruit development. Bamboo, lemon grass, and sugar leaf all benefit from higher nitrogen fertilizers when they are actively growing. Many fertilizers either list what kinds of plants they are formulated for, or what kind of growth they support (such as foliage vs. fruiting).
Slow release fertilizers: If you prefer not to mix liquid fertilizer in when you are watering, consider spreading a long lasting slow release granular or pelleted fertilizer on the soil surface. Slow release fertilizers can also be mixed into the soil at re-potting time. Most slow release fertilizers depend on temperature to regulate nutrient release. Don't expect much performance from the fertilizer until the weather has warmed up. Choose a long release period (such as 6-9 month) to ensure your plants continue to grow well through the summer. Use an appropriate formulation for what you are growing. Fruiting plants need a different balance of nutrients than foliage plants.
Continue pruning as needed, or as time permits. The best time to start pruning stone fruits is as the buds swell. This is because the wounds seal themselves more quickly, reducing opportunity for fungal infections to occur. If you are growing tip-bearing apples such as Thompkins King and want to encourage them to branch, wait until new growth has extended 4-6 inches, then make heading cuts into last year's wood to encourage branching where needed.
As spring progresses, even though many of your plants have started to grow, pruning may continue. Avoid heavy bleeders though, such as grapes, kiwi, and maples, the wounds seal more slowly and produce a lot of sap during their first flush of spring growth. On the other hand, early blooming shrubs, such as forsythia, winter jasmine and flowering quince, are best pruned immediately after they are done blooming, because they set flower buds for next springs bloom on this year's new growth.
Japanese wisteria (wisteria floribunda) have the longest flower racemes of the wisteria, when they are pruned so the flowers hang unimpeded they are particularly beautiful in the spring. Immediately following the bloom thin out crowded shoots and reshape the main framework as needed so next years flowers will hang freely. Retain some of the short lateral shoots that are 1 to several years old, where next years flowers will be born. In late spring cut the vigorous new shoots that tend to grow back to 3-5 buds. More vigorous growth will occur, so again in mid-summer and early fall cut long thin shoots back to 3-5 buds to keep the vines neat. Many of those shortened shoots will also initiate flower buds. Thin out alternate stems where shoots are crowded together.
Now is a good time to look over your stored irrigation equipment and order replacement parts, or parts for new plantings going in this year. In warmer drier locations it may be time to install (re-install) systems and start irrigating. We purchase a lot of our drip irrigation equipment from Dripworks. Call them at 800 522 3747 and they will help you pick out what you need.
In warmer drier locations regular irrigation of new plants is essential for establishment, and may also be necessary for mature plants to thrive. Provide enough water to penetrate the soil to 1 foot deep, then wait to irrigate until the soil has begun to dry out about 6” below the surface. Check the moisture content of the soil by poking your finger in to a depth of about 4-6”. It is hard to sense wet or dry with your finger, but it is easy to sense temperature. If it feels cooler than the air temperature there is generally plenty of water available, if the soil feels closer to air temperature then it is time to water again. Mulching the soil surface with bulky material, such as wood chips or straw, reduces moisture loss from the soil surface. Mulching is particularly beneficial in locations that will experience limited water availability in the summer.
I found two versions of Elderberry Flower Fritters for you to try when your elderberries come into bloom. One was shared with me by a customer who grew up in Denmark, where elderberry is a traditional culinary and medicinal plant. He told me to expect the fritters to taste like the fragrance in the blossoms. He recommended the green leaIved Sambucus nigra elderberries (the type he grew up with), which he felt had more pleasant smelling blossoms. You might also enjoy the lemony fragrance of the Black Beauty S. nigra, while others may prefer the blossoms of the American cultivars, S. canadensis or S. caerulea. Roger Yepsen, in his book "Berries" provides recipes for many of the unusual fruits offered by Raintree Nursery, including elderberry flowers.
Elderflower fritters From a Danish Raintree Nursery customer.
Blossoms (clip at full open, fully fragrant stage, keeping a stem on the back)
Thin crepe batter (use your favorite recipe)
Dip the blossoms in the batter, using the stem as a handle. Fry in oil in a skillet until browned, still using that handle, there is no need to flip. Enjoy with powdered sugar, jam, or plain.
Elderblow Fritters from Berries, by Roger Yepsen (#S042) pg. 93
6-10 elderberry flower clusters
½ cup milk
¼ teaspoon vanilla extract
1/4 teaspoon salt
2 tablespoons sugar
½ cup unbleached white flower
whites of two eggs
cooking oil as needed
Mix the milk, vanilla, egg whites, salt and sugar. Stir in the flour. Pour a few tablespoons of oil in a non-stick skillet. Dip the flower clusters into the batter, and fry over low heat. Add more oil as necessary. Serve warm with maple syrup.
Field Grafting This Spring: Field grafting and top-working of trees can be done in the spring, after danger of hard frost is past. Field grafting is done to add a pollenizer to an existing tree or just add more varieties to a tree. You can also graft on to a rootstock already established in the ground. Rootstocks may be from previously grafted trees on which the graft failed, or intentionally planted rootstock. To do this grafting, you will have had to collect dormant scionwood in the winter and stored it in the refrigerator. Refer to the December Growing Tips, grafting tips section, for collection instructions. Timing of the grafting is important. Temperatures need to be warm enough for the graft to heal and not be exposed to damaging freezing temperatures; and yet not so warm that the scion piece you graft on to the tree starts trying to grow before the graft has healed. A good temperature range would be 35-60°F for 3-4 weeks following the graft. Both whip and tongue and cleft graft techniques can be used. If the rootstock is actively growing T-bud and chip bud grafts may also work. The booklet Budding and Grafting (#S050) provides instructions. You may also be able to find a local class or someone to help you through your local co-operative extension office or local gardening clubs.
Top Working is done when the variety on the tree is no longer desired, but the tree has a good shape and the tree and root system are otherwise healthy. A new, desired variety is grafted to the tree in enough places to create a new top framework, leaving enough of the original tree to sustain it until the new variety takes over. Top working is done in the spring to help reduce the amount of shock the tree will experience from the amount of wood that was removed. Commercial orchardists use this technique to be quickly back in full production.
Care of last summer's bud grafts: If you did a bud graft last summer or fall it is time to start checking it. As soon as new growth appears on the rootstock it is time to cut the rootstock back, just above the bud you grafted.